Publications by authors named "Mutsumi Watanabe"

67 Publications

Assessing Dynamic Changes of Taste-Related Primary Metabolism During Ripening of Durian Pulp Using Metabolomic and Transcriptomic Analyses.

Front Plant Sci 2021 18;12:687799. Epub 2021 Jun 18.

Molecular Crop Research Unit, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.

Durian is an economically important fruit of Southeast Asia. There is, however, a lack of in-depth information on the alteration of its metabolic networks during ripening. Here, we annotated 94 ripening-associated metabolites from the pulp of durian cv. Monthong fruit at unripe and ripe stages, using capillary electrophoresis- and gas chromatography- time-of-flight mass spectrometry, specifically focusing on taste-related metabolites. During ripening, sucrose content increased. Change in raffinose-family oligosaccharides are reported herein for the first time. The malate and succinate contents increased, while those of citrate, an abundant organic acid, were unchanged. Notably, most amino acids increased, including isoleucine, leucine, and valine, whereas aspartate decreased, and glutamate was unchanged. Furthermore, transcriptomic analysis was performed to analyze the dynamic changes in sugar metabolism, glycolysis, TCA cycle, and amino acid pathways to identify key candidate genes. Taken together, our results elucidate the fundamental taste-related metabolism of durian, which can be exploited to develop durian metabolic and genetic markers in the future.
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http://dx.doi.org/10.3389/fpls.2021.687799DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8250156PMC
June 2021

Metabolism and Regulatory Functions of -Acetylserine, -Adenosylmethionine, Homocysteine, and Serine in Plant Development and Environmental Responses.

Front Plant Sci 2021 7;12:643403. Epub 2021 May 7.

RIKEN Center for Sustainable Resource Science, Yokohama, Japan.

The metabolism of an organism is closely related to both its internal and external environments. Metabolites can act as signal molecules that regulate the functions of genes and proteins, reflecting the status of these environments. This review discusses the metabolism and regulatory functions of -acetylserine (OAS), -adenosylmethionine (AdoMet), homocysteine (Hcy), and serine (Ser), which are key metabolites related to sulfur (S)-containing amino acids in plant metabolic networks, in comparison to microbial and animal metabolism. Plants are photosynthetic auxotrophs that have evolved a specific metabolic network different from those in other living organisms. Although amino acids are the building blocks of proteins and common metabolites in all living organisms, their metabolism and regulation in plants have specific features that differ from those in animals and bacteria. In plants, cysteine (Cys), an S-containing amino acid, is synthesized from sulfide and OAS derived from Ser. Methionine (Met), another S-containing amino acid, is also closely related to Ser metabolism because of its thiomethyl moiety. Its S atom is derived from Cys and its methyl group from folates, which are involved in one-carbon metabolism with Ser. One-carbon metabolism is also involved in the biosynthesis of AdoMet, which serves as a methyl donor in the methylation reactions of various biomolecules. Ser is synthesized in three pathways: the phosphorylated pathway found in all organisms and the glycolate and the glycerate pathways, which are specific to plants. Ser metabolism is not only important in Ser supply but also involved in many other functions. Among the metabolites in this network, OAS is known to function as a signal molecule to regulate the expression of OAS gene clusters in response to environmental factors. AdoMet regulates amino acid metabolism at enzymatic and translational levels and regulates gene expression as methyl donor in the DNA and histone methylation or after conversion into bioactive molecules such as polyamine and ethylene. Hcy is involved in Met-AdoMet metabolism and can regulate Ser biosynthesis at an enzymatic level. Ser metabolism is involved in development and stress responses. This review aims to summarize the metabolism and regulatory functions of OAS, AdoMet, Hcy, and Ser and compare the available knowledge for plants with that for animals and bacteria and propose a future perspective on plant research.
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http://dx.doi.org/10.3389/fpls.2021.643403DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8137854PMC
May 2021

Diversity of Chemical Structures and Biosynthesis of Polyphenols in Nut-Bearing Species.

Front Plant Sci 2021 6;12:642581. Epub 2021 Apr 6.

Graduate School of Biological Science, Nara Institute of Science and Technology, Ikoma, Japan.

Nuts, such as peanut, almond, and chestnut, are valuable food crops for humans being important sources of fatty acids, vitamins, minerals, and polyphenols. Polyphenols, such as flavonoids, stilbenoids, and hydroxycinnamates, represent a group of plant-specialized (secondary) metabolites which are characterized as health-beneficial antioxidants within the human diet as well as physiological stress protectants within the plant. In food chemistry research, a multitude of polyphenols contained in culinary nuts have been studied leading to the identification of their chemical properties and bioactivities. Although functional elucidation of the biosynthetic genes of polyphenols in nut species is crucially important for crop improvement in the creation of higher-quality nuts and stress-tolerant cultivars, the chemical diversity of nut polyphenols and the key biosynthetic genes responsible for their production are still largely uncharacterized. However, current technical advances in whole-genome sequencing have facilitated that nut plant species became model plants for omics-based approaches. Here, we review the chemical diversity of seed polyphenols in majorly consumed nut species coupled to insights into their biological activities. Furthermore, we present an example of the annotation of key genes involved in polyphenolic biosynthesis in peanut using comparative genomics as a case study outlining how we are approaching omics-based approaches of the nut plant species.
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http://dx.doi.org/10.3389/fpls.2021.642581DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8056029PMC
April 2021

Cross-Species Metabolic Profiling of Floral Specialized Metabolism Facilitates Understanding of Evolutional Aspects of Metabolism Among Brassicaceae Species.

Front Plant Sci 2021 31;12:640141. Epub 2021 Mar 31.

Graduate School of Biological Science, Nara Institute of Science and Technology (NAIST), Ikoma, Japan.

Plants produce a variety of floral specialized (secondary) metabolites with roles in several physiological functions, including light-protection, attraction of pollinators, and protection against herbivores. Pigments and volatiles synthesized in the petal have been focused on and characterized as major chemical factors influencing pollination. Recent advances in plant metabolomics have revealed that the major floral specialized metabolites found in land plant species are hydroxycinnamates, phenolamides, and flavonoids albeit these are present in various quantities and encompass diverse chemical structures in different species. Here, we analyzed numerous floral specialized metabolites in 20 different Brassicaceae genotypes encompassing both different species and in the case of crop species different cultivars including self-compatible (SC) and self-incompatible (SI) species by liquid chromatography-mass spectrometry (LC-MS). Of the 228 metabolites detected in flowers among 20 Brassicaceae species, 15 metabolite peaks including one phenylacyl-flavonoids and five phenolamides were detected and annotated as key metabolites to distinguish SC and SI plant species, respectively. Our results provide a family-wide metabolic framework and delineate signatures for compatible and incompatible genotypes thereby providing insight into evolutionary aspects of floral metabolism in Brassicaceae species.
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http://dx.doi.org/10.3389/fpls.2021.640141DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8045754PMC
March 2021

Differences in impact on adjacent compartments in medial unicompartmental knee arthroplasty versus high tibial osteotomy with identical valgus alignment.

Knee 2021 Mar 3;29:241-250. Epub 2021 Mar 3.

Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.

Background: It is unclear why medial unicompartmental knee arthroplasty (UKA) with postoperative valgus alignment causes adjacent compartment osteoarthritis more often than high tibial osteotomy (HTO) for moderate medial osteoarthritis of the knee with varus deformity. This study used a computer simulation to evaluate differences in knee conditions between UKA and HTO with identical valgus alignment.

Methods: Dynamic musculoskeletal computer analyses of gait were performed. The hip-knee-ankle angle in fixed-bearing UKA was changed from neutral to 7° valgus by changing the tibial insert thickness. The hip-knee-ankle angle in open-wedge HTO was also changed from neutral to 7° valgus by opening the osteotomy gap.

Results: The lateral tibiofemoral contact forces in HTO were larger than those in UKA until moderate valgus alignments. However, the impact of valgus alignment on increasing lateral forces was more pronounced in UKA, which ultimately demonstrated a larger lateral force than HTO. Valgus alignment in UKA caused progressive ligamentous tightness, including that of the anterior cruciate ligament, resulting in compression of the lateral tibiofemoral compartment. Simultaneously, patellofemoral shear forces were slightly increased and excessive external femoral rotation against the tibia occurred due to the flat medial tibial insert surface and decreased lateral compartment congruency. By contrast, only lateral femoral slide against the tibia occurred in excessively valgus-aligned HTO.

Conclusions: In contrast to extra-articular correction in HTO, which results from opening the osteotomy gap, intra-articular valgus correction in UKA with thicker tibial inserts caused progressive ligamentous tightness and kinematic abnormalities, resulting in early osteoarthritis progression into adjacent compartments.
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http://dx.doi.org/10.1016/j.knee.2021.02.017DOI Listing
March 2021

Developmental stage-specific metabolite signatures in Arabidopsis thaliana under optimal and mild nitrogen limitation.

Plant Sci 2021 Feb 19;303:110746. Epub 2020 Nov 19.

Max Planck Institute of Molecular Plant Physiology, Potsdam, Germany. Electronic address:

Metabolites influence flowering time, and thus are among the major determinants of yield. Despite the reported role of trehalose 6-phosphate and nitrate signaling on the transition from the vegetative to the reproductive phase, little is known about other metabolites contributing and responding to developmental phase changes. To increase our understanding which metabolic traits change throughout development in Arabidopsis thaliana and to identify metabolic markers for the vegetative and reproductive phases, especially among individual amino acids (AA), we profiled metabolites of plants grown in optimal (ON) and limited nitrogen (N) (LN) conditions, the latter providing a mild but consistent limitation of N. We found that although LN plants adapt their growth to a decreased level of N, their metabolite profiles are strongly distinct from ON plant profiles, with N as the driving factor for the observed differences. We demonstrate that the vegetative and the reproductive phase are not only marked by growth parameters such as biomass and rosette area, but also by specific metabolite signatures including specific single AA. In summary, we identified N-dependent and -independent indicators manifesting developmental stages, indicating that the plant's metabolic status also reports on the developmental phases.
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http://dx.doi.org/10.1016/j.plantsci.2020.110746DOI Listing
February 2021

Large medial proximal tibial angles cause excessively medial tibiofemoral contact forces and abnormal knee kinematics following open-wedge high tibial osteotomy.

Clin Biomech (Bristol, Avon) 2020 12 1;80:105190. Epub 2020 Oct 1.

Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.

Background: Recurrent varus deformity and poor outcome sometimes occur following open-wedge high tibial osteotomy, but the mechanism remains unclear. The hypothesis of this study was that an excessively large medial proximal tibial angle with lateral joint surface inclination can worsen postoperative knee biomechanics.

Methods: A computer-simulated knee model was validated based on a volunteer knee. Osteotomy models with medial proximal tibial angles ranging from 90° to 97° in 1° increments were developed. Varus alignment correction of the distal femur was performed in each model to maintain identical coronal alignment passing through a point 62.5% lateral to the tibial plateau. The peak tibiofemoral contact forces and knee kinematics were compared in each model during walking and squatting.

Findings: All the osteotomy models demonstrated higher peak contact forces on the lateral tibiofemoral joints than on the medial tibiofemoral joints during walking. However, larger medial proximal tibial angles caused excessive increases in medial tibiofemoral contact forces, and the dominant tibiofemoral contact forces shifted to the medial side. Increased medial proximal tibial angles also caused progressive medial collateral ligament tension in knee flexion, but partial medial collateral ligament release effectively reduced medial tibiofemoral contact forces. Models with large medial proximal tibial angles showed nonphysiological roll-forward of the lateral femoral condyle during squatting and no screw-home movement around knee extension.

Interpretation: Excessively large medial proximal tibial angles following open-wedge high tibial osteotomy resulted in increased medial tibiofemoral contact forces and abnormal knee kinematics during knee flexion due to medial joint line elevation and ligament imbalance.
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http://dx.doi.org/10.1016/j.clinbiomech.2020.105190DOI Listing
December 2020

Association of foveal avascular zone with the metamorphopsia in epiretinal membrane.

Sci Rep 2020 10 13;10(1):17092. Epub 2020 Oct 13.

Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.

This study was to investigate the relationship between the metamorphopsia and foveal avascular zone (FAZ) parameter in eyes with epiratinal membrane (ERM). We studied patients with an ERM visited retinal service unit at the Kagoshima University Hospital or Shirai Hospital. The best-corrected visual acuity (BCVA), and the degree of metamorphopsia by M -CHARTS™ were evaluated. The 3 × 3 mm optical coherence tomography angiography (OCTA) images of the superficial layer were obtained. Area (mm), the circularity, eigen value were calculated using ImageJ software. The relationship between visual function, such as best corrected visual acuity (BCVA) and metamorphopsia, and FAZ parameters were studied by Pearson's correlational coefficient. Fifty-four eyes of 51 patients (24 men and 27 women) with an ERM were studied. The mean age of the patients was 69.6 ± 8.20 years. The mean BCVA and metamorphopsia score was 0.31 ± 0.29 logMAR units and 0.49 ± 0.42. There was no significant relationship between BCVA and FAZ parameters. While, metamorphopsia score was significantly and negatively correlated with all of FAZ parameters (area R = - 0.491, P < 0.001; circularity R = - 0.385, P = 0.004; eigenvalue ratio R = - 0.341; P = 0.012). Multiple regression analysis showed the FAZ area was solely and significantly correlated with metamorphopsia score (β - 0.479, P < 0.001). The size but not the shape of the FAZ was significantly correlated with the degree of metamorphopsia suggesting that it could be an objective parameter of metamorphopsia in ERM patients.
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http://dx.doi.org/10.1038/s41598-020-74190-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7555497PMC
October 2020

Abnormal knee kinematics caused by mechanical alignment in symmetric bicruciate-retaining total knee arthroplasty are alleviated by kinematic alignment.

Knee 2020 Oct 15;27(5):1385-1395. Epub 2020 Aug 15.

Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.

Background: Bicruciate-retaining total knee arthroplasty (BCR-TKA) was developed to maintain anterior cruciate ligament function and thus reproduce natural knee kinematics postoperatively. Traditional surgical techniques, however, may cause several complications secondary to kinematic conflict and ligament overtension. The objective of this study was to use a computer simulation of symmetric BCR-TKA to evaluate the effects of alternative surgical techniques on knee kinematics and ligaments.

Methods: A musculoskeletal computer model of a healthy knee was constructed and was used to simulate a BCR model with mechanical alignment (MA). Five adjusted models were investigated, characterized, respectively, by kinematic alignment (KA), two degrees increased tibial slope, two-millimeter distal setting of the tibial component, and an undersized femoral component with either MA or KA.

Results: All models exhibited a normal femoral position against the tibia at knee extension, with no anterior paradoxical motion during mid-flexion. The healthy knee model showed medial pivot motion and rollback. In contrast, the BCR MA model demonstrated abnormal bi-condylar rollback with excessive tensions of the lateral collateral ligament and posterior cruciate ligament during knee flexion, whereas the undersized femoral model with MA partly reduced both tensions. The BCR KA model retained relatively physiological kinematics and suppressed excessive ligament tensions. However, no adjusted model completely reproduced healthy knee conditions.

Conclusions: The BCR MA model showed abnormal biomechanics due to kinematic conflict between the retained ligaments and the replaced joint surface. Surgeons using symmetric BCR-TKA should consider using the KA method to achieve sufficient ligament laxity throughout knee flexion.
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http://dx.doi.org/10.1016/j.knee.2020.07.099DOI Listing
October 2020

Length of anterior cruciate ligament affects knee kinematics and kinetics using a musculoskeletal computer simulation model.

J Orthop 2020 Sep-Oct;21:370-374. Epub 2020 Aug 6.

Department of Orthopaedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoin-kawaharacho, Sakyo-ku, Kyoto, 6068507, Japan.

Introduction: The tension of anterior cruciate ligament (ACL) graft has an important role in antero-posterior (AP) and rotational stability of the knee. The purposes of this study were to analyze the kinematics and kinetics of normal knee models with loose and tight ACL tension, and to evaluate the effect of the tension of ACL on knee kinematics and kinetics.

Materials And Methods: Slack and tight ACL models were constructed in a musculoskeletal computer simulation. The effect of ACL tension on kinematics, and femorotibial contact force during various activities was analyzed.

Results: During stair descent activity in the slack ACL models, the lateral femoral condyles were positioned posterior, and more external rotation of the femur was observed in comparison with the normal model. The contact forces at the lateral compartment in the tight models increased during all activities, and the tension of the medial collateral ligament (MCL) in the slack models increased during the stair descent activity, compared with the normal knee model.

Conclusion: AP and rotational instability and excessive MCL tension were observed in the ACL slack knees especially during stair descent movement, whereas the tibiofemoral contact force of the lateral compartment increased in the tight ACL knees.
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http://dx.doi.org/10.1016/j.jor.2020.08.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7453099PMC
August 2020

Cross-Species Comparison of Fruit-Metabolomics to Elucidate Metabolic Regulation of Fruit Polyphenolics Among Solanaceous Crops.

Metabolites 2020 May 19;10(5). Epub 2020 May 19.

Graduate School of Science and Technology, Nara Institute of Science and Technology (NAIST), Ikoma, Nara 630-0192, Japan.

Many solanaceous crops are an important part of the human daily diet. Fruit polyphenolics are plant specialized metabolites that are recognized for their human health benefits and their defensive role against plant abiotic and biotic stressors. Flavonoids and chlorogenates are the major polyphenolic compounds found in solanaceous fruits that vary in quantity, physiological function, and structural diversity among and within plant species. Despite their biological significance, the elucidation of metabolic shifts of polyphenols during fruit ripening in different fruit tissues, has not yet been well-characterized in solanaceous crops, especially at a cross-species and cross-cultivar level. Here, we performed a cross-species comparison of fruit-metabolomics to elucidate the metabolic regulation of fruit polyphenolics from three representative crops of Solanaceae (tomato, eggplant, and pepper), and a cross-cultivar comparison among different pepper cultivars ( cv.) using liquid chromatography-mass spectrometry (LC-MS). We observed a metabolic trade-off between hydroxycinnamates and flavonoids in pungent pepper and anthocyanin-type pepper cultivars and identified metabolic signatures of fruit polyphenolics in each species from each different tissue-type and fruit ripening stage. Our results provide additional information for metabolomics-assisted crop improvement of solanaceous fruits towards their improved nutritive properties and enhanced stress tolerance.
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http://dx.doi.org/10.3390/metabo10050209DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7281770PMC
May 2020

Diversity of anthocyanin and proanthocyanin biosynthesis in land plants.

Curr Opin Plant Biol 2020 06 5;55:93-99. Epub 2020 May 5.

Graduate School of Biological Science, Nara Institute of Science and Technology (NAIST), Ikoma, 630-0192 Japan. Electronic address:

Anthocyanins and proanthocyanidins are among the most numerous and widely distributed pigments in land plants. Given that these pigments are the valuable compounds, as stress protectants and health-promoting components because of their potent antioxidant activity, several metabolic engineering approaches focusing on these compounds have been attempted. Currently, the difference in biological functions between flavonoid decorations is focused, because some aglycone decorations were found to be key factors rendering physiological functions against environmental stresses. Therefore, metabolic diversity and functional genomics approaches focusing on anthocyanin decoration should be reconsidered. Additionally, since the production of anthocyanins and proanthocyanidins in plants is often represented in a tissue-specific manner and by stress induction, elucidation of the specific regulatory mechanisms of how these pathways have been evolved, is highly important. Here, we review current knowledge of the diversity of chemical structure and regulators of anthocyanin/proanthocyanin biosynthesis with cross-species comparison to assess metabolic evolution.
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http://dx.doi.org/10.1016/j.pbi.2020.04.001DOI Listing
June 2020

Metabolomic markers and physiological adaptations for high phosphate utilization efficiency in rice.

Plant Cell Environ 2020 09 7;43(9):2066-2079. Epub 2020 Jul 7.

Japan International Research Center for Agricultural Sciences (JIRCAS), Tsukuba, Japan.

Utilizing phosphate more efficiently is crucial for sustainable crop production. Highly efficient rice (Oryza sativa) cultivars have been identified and this study aims to identify metabolic markers associated with P utilization efficiency (PUE). P deficiency generally reduced leaf P concentrations and CO assimilation rates but efficient cultivars were reducing leaf P concentrations further than inefficient ones while maintaining similar CO assimilation rates. Adaptive changes in carbon metabolism were detected but equally in efficient and inefficient cultivar groups. Groups furthermore did not differ with respect to partial substitutions of phospholipids by sulfo- and galactolipids. Metabolites significantly more abundant in the efficient group, such as sinapate, benzoate and glucoronate, were related to antioxidant defence and may help alleviating oxidative stress caused by P deficiency. Sugar alcohols ribitol and threitol were another marker metabolite for higher phosphate efficiency as were several amino acids, especially threonine. Since these metabolites are not known to be associated with P deficiency, they may provide novel clues for the selection of more P efficient genotypes. In conclusion, metabolite signatures detected here were not related to phosphate metabolism but rather helped P efficient lines to keep vital processes functional under the adverse conditions of P starvation.
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http://dx.doi.org/10.1111/pce.13777DOI Listing
September 2020

Exploiting Natural Variation in Tomato to Define Pathway Structure and Metabolic Regulation of Fruit Polyphenolics in the Lycopersicum Complex.

Mol Plant 2020 07 16;13(7):1027-1046. Epub 2020 Apr 16.

Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Muehlenberg 1, 14476 Potsdam-Golm, Germany; Institute of Plant Systems Biology, 4000 Plovdiv, Bulgaria. Electronic address:

While the structures of plant primary metabolic pathways are generally well defined and highly conserved across species, those defining specialized metabolism are less well characterized and more highly variable across species. In this study, we investigated polyphenolic metabolism in the lycopersicum complex by characterizing the underlying biosynthetic and decorative reactions that constitute the metabolic network of polyphenols across eight different species of tomato. For this purpose, GC-MS- and LC-MS-based metabolomics of different tissues of Solanum lycopersicum and wild tomato species were carried out, in concert with the evaluation of cross-hybridized microarray data for MapMan-based transcriptomic analysis, and publicly available RNA-sequencing data for annotation of biosynthetic genes. The combined data were used to compile species-specific metabolic networks of polyphenolic metabolism, allowing the establishment of an entire pan-species biosynthetic framework as well as annotation of the functions of decoration enzymes involved in the formation of metabolic diversity of the flavonoid pathway. The combined results are discussed in the context of the current understanding of tomato flavonol biosynthesis as well as a global view of metabolic shifts during fruit ripening. Our results provide an example as to how large-scale biology approaches can be used for the definition and refinement of large specialized metabolism pathways.
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http://dx.doi.org/10.1016/j.molp.2020.04.004DOI Listing
July 2020

Functional Features of TREHALOSE-6-PHOSPHATE SYNTHASE1, an Essential Enzyme in Arabidopsis.

Plant Cell 2020 06 10;32(6):1949-1972. Epub 2020 Apr 10.

Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany

In Arabidopsis (), TREHALOSE-6-PHOSPHATE SYNTHASE1 (TPS1) catalyzes the synthesis of the sucrose-signaling metabolite trehalose 6-phosphate (Tre6P) and is essential for embryogenesis and normal postembryonic growth and development. To understand its molecular functions, we transformed the embryo-lethal null mutant with various forms of TPS1 and with a heterologous TPS (OtsA) from , under the control of the promoter, and tested for complementation. TPS1 protein localized predominantly in the phloem-loading zone and guard cells in leaves, root vasculature, and shoot apical meristem, implicating it in both local and systemic signaling of Suc status. The protein is targeted mainly to the nucleus. Restoring Tre6P synthesis was both necessary and sufficient to rescue the mutant through embryogenesis. However, postembryonic growth and the sucrose-Tre6P relationship were disrupted in some complementation lines. A point mutation (A119W) in the catalytic domain or truncating the C-terminal domain of TPS1 severely compromised growth. Despite having high Tre6P levels, these plants never flowered, possibly because Tre6P signaling was disrupted by two unidentified disaccharide-monophosphates that appeared in these plants. The noncatalytic domains of TPS1 ensure its targeting to the correct subcellular compartment and its catalytic fidelity and are required for appropriate signaling of Suc status by Tre6P.
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http://dx.doi.org/10.1105/tpc.19.00837DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7268806PMC
June 2020

Genetic Manipulation of Transcriptional Regulators Alters Nicotine Biosynthesis in Tobacco.

Plant Cell Physiol 2020 Jun;61(6):1041-1053

Department of Biological Science, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma, Nara, 630-0101 Japan.

The toxic alkaloid nicotine is produced in the roots of Nicotiana species and primarily accumulates in leaves as a specialized metabolite. A series of metabolic and transport genes involved in the nicotine pathway are coordinately upregulated by a pair of jasmonate-responsive AP2/ERF-family transcription factors, NtERF189 and NtERF199, in the roots of Nicotiana tabacum (tobacco). In this study, we explored the potential of manipulating the expression of these transcriptional regulators to alter nicotine biosynthesis in tobacco. The transient overexpression of NtERF189 led to alkaloid production in the leaves of Nicotiana benthamiana and Nicotiana alata. This ectopic production was further enhanced by co-overexpressing a gene encoding a basic helix-loop-helix-family MYC2 transcription factor. Constitutive and leaf-specific overexpression of NtERF189 increased the accumulation of foliar alkaloids in transgenic tobacco plants but negatively affected plant growth. By contrast, in a knockout mutant of NtERF189 and NtERF199 obtained through CRISPR/Cas9-based genome editing, alkaloid levels were drastically reduced without causing major growth defects. Metabolite profiling revealed the impact of manipulating the nicotine pathway on a wide range of nitrogen- and carbon-containing metabolites. Our findings provide insights into the biotechnological applications of engineering metabolic pathways by targeting transcription factors.
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http://dx.doi.org/10.1093/pcp/pcaa036DOI Listing
June 2020

H Transport by K EXCHANGE ANTIPORTER3 Promotes Photosynthesis and Growth in Chloroplast ATP Synthase Mutants.

Plant Physiol 2020 04 10;182(4):2126-2142. Epub 2020 Feb 10.

Max Planck Institute of Molecular Plant Physiology, Wissenschaftspark Golm, Am Mühlenberg 1, 14476 Potsdam, Germany

The composition of the thylakoid proton motive force (pmf) is regulated by thylakoid ion transport. Passive ion channels in the thylakoid membrane dissipate the membrane potential (Δψ) component to allow for a higher fraction of pmf stored as a proton concentration gradient (ΔpH). K/H antiport across the thylakoid membrane via K+ EXCHANGE ANTIPORTER3 (KEA3) instead reduces the ΔpH fraction of the pmf. Thereby, KEA3 decreases nonphotochemical quenching (NPQ), thus allowing for higher light use efficiency, which is particularly important during transitions from high to low light. Here, we show that in the background of the Arabidopsis () chloroplast (cp)ATP synthase assembly mutant , with decreased cpATP synthase activity and increased pmf amplitude, KEA3 plays an important role for photosynthesis and plant growth under steady-state conditions. By comparing single with double mutants, we demonstrate that in the background loss of KEA3 causes a strong growth penalty. This is due to a reduced photosynthetic capacity of mutants, as these plants have a lower lumenal pH than mutants, and thus show substantially increased pH-dependent NPQ and decreased electron transport through the cytochrome complex. Overexpression of in the background reduces pH-dependent NPQ and increases photosystem II efficiency. Taken together, our data provide evidence that under conditions where cpATP synthase activity is low, a KEA3-dependent reduction of ΔpH benefits photosynthesis and growth.
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http://dx.doi.org/10.1104/pp.19.01561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7140953PMC
April 2020

Non-aqueous fractionation revealed changing subcellular metabolite distribution during apple fruit development.

Hortic Res 2019 11;6:98. Epub 2019 Aug 11.

1Division of Mechatronics, Biostatistics and Sensors (MeBioS), Department of Biosystems (BIOSYST), KU Leuven, Leuven, Belgium.

In developing apple fruit, metabolic compartmentation is poorly understood due to the lack of experimental data. Distinguishing subcellular compartments in fruit using non-aqueous fractionation has been technically difficult due to the excess amount of sugars present in the different subcellular compartments limiting the resolution of the technique. The work described in this study represents the first attempt to apply non-aqueous fractionation to developing apple fruit, covering the major events occurring during fruit development (cell division, cell expansion, and maturation). Here we describe the non-aqueous fractionation method to study the subcellular compartmentation of metabolites during apple fruit development considering three main cellular compartments (cytosol, plastids, and vacuole). Evidence is presented that most of the sugars and organic acids were predominantly located in the vacuole, whereas some of the amino acids were distributed between the cytosol and the vacuole. The results showed a shift in the plastid marker from the lightest fractions in the early growth stage to the dense fractions in the later fruit growth stages. This implies that the accumulation of starch content with progressing fruit development substantially influenced the distribution of plastidial fragments within the non-aqueous density gradient applied. Results from this study provide substantial baseline information on assessing the subcellular compartmentation of metabolites in apple fruit in general and during fruit growth in particular.
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http://dx.doi.org/10.1038/s41438-019-0178-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6804870PMC
August 2019

Sulphur systems biology-making sense of omics data.

J Exp Bot 2019 08;70(16):4155-4170

Max Planck Institute of Molecular Plant Physiology, Potsdam-Golm, Germany.

Systems biology approaches have been applied over the last two decades to study plant sulphur metabolism. These 'sulphur-omics' approaches have been developed in parallel with the advancing field of systems biology, which is characterized by permanent improvements of high-throughput methods to obtain system-wide data. The aim is to obtain a holistic view of sulphur metabolism and to generate models that allow predictions of metabolic and physiological responses. Besides known sulphur-responsive genes derived from previous studies, numerous genes have been identified in transcriptomics studies. This has not only increased our knowledge of sulphur metabolism but has also revealed links between metabolic processes, thus indicating a previously unexpected complex interconnectivity. The identification of response and control networks has been supported through metabolomics and proteomics studies. Due to the complex interlacing nature of biological processes, experimental validation using targeted or systems approaches is ongoing. There is still room for improvement in integrating the findings from studies of metabolomes, proteomes, and metabolic fluxes into a single unifying concept and to generate consistent models. We therefore suggest a joint effort of the sulphur research community to standardize data acquisition. Furthermore, focusing on a few different model plant systems would help overcome the problem of fragmented data, and would allow us to provide a standard data set against which future experiments can be designed and compared.
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http://dx.doi.org/10.1093/jxb/erz260DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6698701PMC
August 2019

Classical target coronal alignment in high tibial osteotomy demonstrates validity in terms of knee kinematics and kinetics in a computer model.

Knee Surg Sports Traumatol Arthrosc 2020 May 21;28(5):1568-1578. Epub 2019 Jun 21.

Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.

Purpose: The purpose of this study was to determine the ideal coronal alignment under dynamic conditions after open-wedge high tibial osteotomy (OWHTO). It was hypothesised that, although the classical target alignment was based on experimental evidence, it would demonstrate biomechanical validity.

Methods: Musculoskeletal computer models were analysed with various degrees of coronal correction in OWHTO during gait and squat, specifically with the mechanical axis passing through points at 40%, 50%, 60%, 62.5%, 70%, and 80% of the tibial plateau from the medial edge, defined as the weight-bearing line percentage (WBL%). The peak load on the lateral tibiofemoral (TF) joint, the medial collateral ligament (MCL), and anterior cruciate ligament (ACL) tensions, and knee kinematics with or without increased posterior tibial slope (PTS) were evaluated.

Results: The classical alignment with WBL62.5% achieved sufficient load on the lateral TF joint and maintained normal knee kinematics after OWHTO. However, over-correction with WBL80% caused an excessive lateral load and non-physiological kinematics. Increased WBL% resulted in increased MCL tension due to lateral femoral movement against the tibia. With WBL80%, abnormal contact between the medial femoral condyle and the medial intercondylar eminence of the tibia occurred at knee extension. The screw-home movement around knee extension and the TF rotational angle during flexion were reduced as WBL% increased. Increased PTS was associated with increased ACL tension and decreased TF rotation angle because of ligamentous imbalance.

Conclusions: The classical target alignment demonstrated validity in OWHTO, and over-correction should be avoided as it negatively impacts clinical outcome.

Level Of Evidence: IV.
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http://dx.doi.org/10.1007/s00167-019-05575-3DOI Listing
May 2020

The ABCB7-Like Transporter PexA in Is Involved in the Translocation of Reactive Sulfur Species.

Front Microbiol 2019 13;10:406. Epub 2019 Mar 13.

Institute of Biochemistry and Biology, Department of Molecular Enzymology, University of Potsdam, Potsdam, Germany.

The mitochondrial ATP-binding cassette (ABC) transporters ABCB7 in humans, Atm1 in yeast and ATM3 in plants, are highly conserved in their overall architecture and particularly in their glutathione binding pocket located within the transmembrane spanning domains. These transporters have attracted interest in the last two decades based on their proposed role in connecting the mitochondrial iron-sulfur (Fe-S) cluster assembly with its cytosolic Fe-S cluster assembly (CIA) counterpart. So far, the specific compound that is transported across the membrane remains unknown. In this report we characterized the ABCB7-like transporter Rcc02305 in , which shares 47% amino acid sequence identity with its mitochondrial counterpart. The constructed interposon mutant strain in displayed increased levels of intracellular reactive oxygen species without a simultaneous accumulation of the cellular iron levels. The inhibition of endogenous glutathione biosynthesis resulted in an increase of total glutathione levels in the mutant strain. Bioinformatic analysis of the amino acid sequence motifs revealed a potential aminotransferase class-V pyridoxal-5'-phosphate (PLP) binding site that overlaps with the Walker A motif within the nucleotide binding domains of the transporter. PLP is a well characterized cofactor of L-cysteine desulfurases like IscS and NFS1 which has a role in the formation of a protein-bound persulfide group within these proteins. We therefore suggest renaming the ABCB7-like transporter Rcc02305 in to PexA for PLP binding exporter. We further suggest that this ABC-transporter in is involved in the formation and export of polysulfide species to the periplasm.
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http://dx.doi.org/10.3389/fmicb.2019.00406DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6424863PMC
March 2019

Impact of intraoperative adjustment method for increased flexion gap on knee kinematics after posterior cruciate ligament-sacrificing total knee arthroplasty.

Clin Biomech (Bristol, Avon) 2019 03 27;63:85-94. Epub 2019 Feb 27.

Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.

Background: In general, the flexion gap is larger than the extension gap with posterior cruciate ligament-sacrificing total knee arthroplasty. Several methods compensate for an excessive flexion gap, but their effects are unknown. The purpose of this study was to compare three methods to compensate for an increased flexion gap.

Methods: In this study, squatting in knees with excessive (4 mm) and moderate (2 mm) flexion gaps was simulated in a computer model. Differences in knee kinematics and kinetics with joint line elevation, setting the femoral component in flexion, and using a larger femoral component as compensatory methods were investigated.

Findings: The rotational kinematics during flexion with setting the femoral component in flexion were opposite to those in the other models. Using a larger femoral component resulted in the most physiological motion. The peak anterior translation was 10 mm in the joint line elevation model compared with approximately 6 mm in the other models. In the joint line elevation model, patellofemoral contact stress was excessively increased at 90° of knee flexion. In contrast, tibiofemoral contact stress was higher during knee extension with setting the femoral component in flexion due to anterior impingement. There were few differences in the effect of the three compensatory methods with a moderate flexion gap.

Interpretation: A larger femoral component should be used to compensate for an excessive flexion gap because it has less negative impact on posterior cruciate ligament-sacrificing total knee arthroplasty, whereas any compensation method might be acceptable for a moderate flexion gap.
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http://dx.doi.org/10.1016/j.clinbiomech.2019.02.018DOI Listing
March 2019

Opposite fates of the purine metabolite allantoin under water and nitrogen limitations in bread wheat.

Plant Mol Biol 2019 Mar 5;99(4-5):477-497. Epub 2019 Feb 5.

School of Agriculture Food and Wine, The University of Adelaide, Urrbrae, SA, 5064, Australia.

Key Message: Degradation of nitrogen-rich purines is tightly and oppositely regulated under drought and low nitrogen supply in bread wheat. Allantoin is a key target metabolite for improving nitrogen homeostasis under stress. The metabolite allantoin is an intermediate of the catabolism of purines (components of nucleotides) and is known for its housekeeping role in nitrogen (N) recycling and also for its function in N transport and storage in nodulated legumes. Allantoin was also shown to differentially accumulate upon abiotic stress in a range of plant species but little is known about its role in cereals. To address this, purine catabolic pathway genes were identified in hexaploid bread wheat and their chromosomal location was experimentally validated. A comparative study of two Australian bread wheat genotypes revealed a highly significant increase of allantoin (up to 29-fold) under drought. In contrast, allantoin significantly decreased (up to 22-fold) in response to N deficiency. The observed changes were accompanied by transcriptional adjustment of key purine catabolic genes, suggesting that the recycling of purine-derived N is tightly regulated under stress. We propose opposite fates of allantoin in plants under stress: the accumulation of allantoin under drought circumvents its degradation to ammonium (NH) thereby preventing N losses. On the other hand, under N deficiency, increasing the NH liberated via allantoin catabolism contributes towards the maintenance of N homeostasis.
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http://dx.doi.org/10.1007/s11103-019-00831-zDOI Listing
March 2019

Plasmodium Para-Aminobenzoate Synthesis and Salvage Resolve Avoidance of Folate Competition and Adaptation to Host Diet.

Cell Rep 2019 01;26(2):356-363.e4

Department of Molecular Parasitology, Institute of Biology, Humboldt University, 10115 Berlin, Germany; Parasitology Unit, Max Planck Institute of Infection Biology, 10117 Berlin, Germany.

Folate metabolism is essential for DNA synthesis and a validated drug target in fast-growing cell populations, including tumors and malaria parasites. Genome data suggest that Plasmodium has retained its capacity to generate folates de novo. However, the metabolic plasticity of folate uptake and biosynthesis by the malaria parasite remains unresolved. Here, we demonstrate that Plasmodium uses an aminodeoxychorismate synthase and an aminodeoxychorismate lyase to promote the biogenesis of the central folate precursor para-aminobenzoate (pABA) in the cytoplasm. We show that the parasite depends on de novo folate synthesis only when dietary intake of pABA by the mammalian host is restricted and that only pABA, rather than fully formed folate, is taken up efficiently. This adaptation, which readily adjusts infection to highly variable pABA levels in the mammalian diet, is specific to blood stages and may have evolved to avoid folate competition between the parasite and its host.
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http://dx.doi.org/10.1016/j.celrep.2018.12.062DOI Listing
January 2019

Sulfite Reductase Co-suppression in Tobacco Reveals Detoxification Mechanisms and Downstream Responses Comparable to Sulfate Starvation.

Front Plant Sci 2018 15;9:1423. Epub 2018 Oct 15.

Max Planck Institute of Molecular Plant Physiology, Potsdam, Germany.

Sulfite reductase (SIR) is a key enzyme in higher plants in the assimilatory sulfate reduction pathway. SIR, being exclusively localized in plastids, catalyzes the reduction of sulfite (SO ) to sulfide (S) and is essential for plant life. We characterized transgenic plants leading to co-suppression of the gene in tobacco ( Samsun NN). Co-suppression resulted in reduced but not completely extinguished expression of and in a reduction of SIR activity to about 20-50% of the activity in control plants. The reduction of SIR activity caused chlorotic and necrotic phenotypes in tobacco leaves, but with varying phenotype strength even among clones and increasing from young to old leaves. In transgenic plants compared to control plants, metabolite levels upstream of SIR accumulated, such as sulfite, sulfate and thiosulfate. The levels of downstream metabolites were reduced, such as cysteine, glutathione (GSH) and methionine. This metabolic signature resembles a sulfate deprivation phenotype as corroborated by the fact that -acetylserine (OAS) accumulated. Further, chlorophyll contents, photosynthetic electron transport, and the contents of carbohydrates such as starch, sucrose, fructose, and glucose were reduced. Amino acid compositions were altered in a complex manner due to the reduction of contents of cysteine, and to some extent methionine. Interestingly, sulfide levels remained constant indicating that sulfide homeostasis is crucial for plant performance and survival. Additionally, this allows concluding that sulfide does not act as a signal in this context to control sulfate uptake and assimilation. The accumulation of upstream compounds hints at detoxification mechanisms and, additionally, a control exerted by the downstream metabolites on the sulfate uptake and assimilation system. Co-suppression lines showed increased sensitivity to additionally imposed stresses probably due to the accumulation of reactive compounds because of insufficient detoxification in combination with reduced GSH levels.
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http://dx.doi.org/10.3389/fpls.2018.01423DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6196246PMC
October 2018

Metabolome and Lipidome Profiles of × Twig Tissues During Annual Growth Show Phospholipid-Linked Storage and Mobilization of C, N, and S.

Front Plant Sci 2018 5;9:1292. Epub 2018 Sep 5.

Chair of Tree Physiology, Institute of Forest Sciences, Albert Ludwigs University of Freiburg, Freiburg, Germany.

The temperate climax tree species and the floodplain tree species × possess contrasting phosphorus (P) nutrition strategies. While has been documented to display P storage and mobilization (Netzer et al., 2017), this was not observed for × (Netzer et al., 2018b). Nevertheless, changes in the abundance of organic bound P in gray poplar trees indicated adaptation of the P nutrition to different needs during annual growth. The present study aimed at characterizing seasonal changes in metabolite and lipid abundances in gray poplar and uncovering differences in metabolite requirement due to specific needs depending on the season. Seasonal variations in the abundance of (i) sugar-Ps and phospholipids, (ii) amino acids, (iii) sulfur compounds, and (iv) carbon metabolites were expected. It was hypothesized that seasonal changes in metabolite levels relate to N, S, and C storage and mobilization. Changes in organic metabolites binding P (P) are supposed to support these processes. Variation in triacylglycerols, in sugar-phosphates, in metabolites of the TCA cycle and in the amino acid abundance of poplar twig buds, leaves, bark, and wood were found to be linked to changes in metabolite abundances as well as to C, N, and S storage and mobilization processes. The observed changes support the view of a lack of any P storage in poplar. Yet, during dormancy, contents of phospholipids in twig bark and wood were highest probably due to frost-hardening and to its function in extra-plastidic membranes such as amyloplasts, oleosomes, and protein bodies. Consistent with this assumption, in spring sugar-Ps increased when phospholipids declined and poplar plants entering the vegetative growth period and, hence, metabolic activity increases. These results indicate that poplar trees adopt a policy of P nutrition without P storage and mobilization that is different from their N- and S-nutrition strategies.
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http://dx.doi.org/10.3389/fpls.2018.01292DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6133996PMC
September 2018

Metabolic variation in the pulps of two durian cultivars: Unraveling the metabolites that contribute to the flavor.

Food Chem 2018 Dec 15;268:118-125. Epub 2018 Jun 15.

Department of Biochemistry, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Bangkok 10330, Thailand; Omics Sciences and Bioinformatics Center, Chulalongkorn University, 254 Phayathai Road, Bangkok 10330, Thailand. Electronic address:

Durian (Durio zibethinus M.) is a major economic fruit crop in Thailand. In this study, two popular cultivars, namely Chanee and Mon Thong, were collected from three orchards located in eastern Thailand. The pulp metabolome, including 157 annotated metabolites, was explored using capillary electrophoresis-time of flight/mass spectrometry (CE-TOF/MS). Cultivars and harvest years had more impact on metabolite profile separation than cultivation areas. We identified cultivar-dependent metabolite markers related to durian fruit quality traits, such as nutritional value (pyridoxamine), odor (cysteine, leucine), and ripening process (aminocyclopropane carboxylic acid). Interestingly, durian fruit were found to contain high amounts of γ-glutamylcysteine (810.3 ± 257.5 mg/100 g dry weight) and glutathione (158.1 ± 80.4 mg/100 g dry weight), which act as antioxidants and taste enhancers. This metabolite information could be related to consumer preferences and exploited for durian fruit quality improvement.
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http://dx.doi.org/10.1016/j.foodchem.2018.06.066DOI Listing
December 2018

The Effect of Single and Multiple SERAT Mutants on Serine and Sulfur Metabolism.

Front Plant Sci 2018 28;9:702. Epub 2018 May 28.

Max Planck Institute of Molecular Plant Physiology, Potsdam, Germany.

The gene family of serine acetyltransferases (SERATs) constitutes an interface between the plant pathways of serine and sulfur metabolism. SERATs provide the activated precursor, -acetylserine for the fixation of reduced sulfur into cysteine by exchanging the serine hydroxyl moiety by a sulfhydryl moiety, and subsequently all organic compounds containing reduced sulfur moieties. We investigate here, how manipulation of the SERAT interface results in metabolic alterations upstream or downstream of this boundary and the extent to which the five SERAT isoforms exert an effect on the coupled system, respectively. Serine is synthesized through three distinct pathways while cysteine biosynthesis is distributed over the three compartments cytosol, mitochondria, and plastids. As the respective mutants are viable, all necessary metabolites can obviously cross various membrane systems to compensate what would otherwise constitute a lethal failure in cysteine biosynthesis. Furthermore, given that cysteine serves as precursor for multiple pathways, cysteine biosynthesis is highly regulated at both, the enzyme and the expression level. In this study, metabolite profiles of a mutant series of the gene family displayed that levels of the downstream metabolites in sulfur metabolism were affected in correlation with the reduction levels of SERAT activities and the growth phenotypes, while levels of the upstream metabolites in serine metabolism were unchanged in the mutants compared to wild-type plants. These results suggest that despite of the fact that the two metabolic pathways are directly connected, there seems to be no causal link in metabolic alterations. This might be caused by the difference of their pool sizes or the tight regulation by homeostatic mechanisms that control the metabolite concentration in plant cells. Additionally, growth conditions exerted an influence on metabolic compositions.
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http://dx.doi.org/10.3389/fpls.2018.00702DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5985473PMC
May 2018

Targeted LC-MS Analysis for Plant Secondary Metabolites.

Methods Mol Biol 2018 ;1778:171-181

Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan.

Recent technological developments and methodological advances of both liquid chromatography (LC) and mass spectrometry (MS) have allowed LC-MS-based plant metabolomics to become a common tool for investigating quantity, quality, and chemical diversity of plant metabolites. Targeted LC-MS metabolite analysis focuses on the detection and quantitation of the researcher's target metabolites. Whilst the word "target analysis" has been used for the analytical measurement to obtain the absolute concentrations evaluated by authentic and/or stable-isotope-labeled standards, over time the phrase came to be also used in a broad sense for the measurement of annotatable metabolites by structural information obtained from the combination of different strategies such as MS/MS analysis, reference extracts, mutant analysis and database search. Here, we describe a general protocol for targeted LC-MS metabolite profiling of plant secondary metabolites. Additionally, we introduce some examples of peak annotation using the combination approach.
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http://dx.doi.org/10.1007/978-1-4939-7819-9_12DOI Listing
February 2019

RAPTOR Controls Developmental Growth Transitions by Altering the Hormonal and Metabolic Balance.

Plant Physiol 2018 06 23;177(2):565-593. Epub 2018 Apr 23.

Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany.

Vegetative growth requires the systemic coordination of numerous cellular processes, which are controlled by regulatory proteins that monitor extracellular and intracellular cues and translate them into growth decisions. In eukaryotes, one of the central factors regulating growth is the serine/threonine protein kinase Target of Rapamycin (TOR), which forms complexes with regulatory proteins. To understand the function of one such regulatory protein, Regulatory-Associated Protein of TOR 1B (RAPTOR1B), in plants, we analyzed the effect of mutations on growth and physiology in Arabidopsis () by detailed phenotyping, metabolomic, lipidomic, and proteomic analyses. Mutation of resulted in a strong reduction of TOR kinase activity, leading to massive changes in central carbon and nitrogen metabolism, accumulation of excess starch, and induction of autophagy. These shifts led to a significant reduction of plant growth that occurred nonlinearly during developmental stage transitions. This phenotype was accompanied by changes in cell morphology and tissue anatomy. In contrast to previous studies in rice (), we found that the Arabidopsis mutation did not affect chloroplast development or photosynthetic electron transport efficiency; however, it resulted in decreased CO assimilation rate and increased stomatal conductance. The mutants also had reduced abscisic acid levels. Surprisingly, abscisic acid feeding experiments resulted in partial complementation of the growth phenotypes, indicating the tight interaction between TOR function and hormone synthesis and signaling in plants.
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http://dx.doi.org/10.1104/pp.17.01711DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6001337PMC
June 2018
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