Publications by authors named "Ki-Hong Jung"

113 Publications

Global Identification of Genes Involved in Rice Pollen Germination and Functional Characterization of a Key Member, OsANTH3.

Front Plant Sci 2021 13;12:609473. Epub 2021 Apr 13.

Department of Life Science and Environmental Biochemistry, Life and Industry Convergence Research Institute, Pusan National University, Miryang, South Korea.

Pollen in angiosperms plays a critical role in double fertilization by germinating and elongating pollen tubes rapidly in one direction to deliver sperm. In this process, the secretory vesicles deliver cell wall and plasma membrane materials, and excessive materials are sequestered via endocytosis. However, endocytosis in plants is poorly understood. AP180 N-terminal homology (ANTH) domain-containing proteins function as adaptive regulators for clathrin-mediated endocytosis in eukaryotic systems. Here, we identified 17 ANTH domain-containing proteins from rice based on a genome-wide investigation. Motif and phylogenomic analyses revealed seven asparagine-proline-phenylalanine (NPF)-rich and 10 NPF-less subgroups of these proteins, as well as various clathrin-mediated endocytosis-related motifs in their C-terminals. To investigate their roles in pollen germination, we performed meta-expression analysis of all genes encoding ANTH domain-containing proteins in ( genes) in anatomical samples, including pollen, and identified five mature pollen-preferred genes. The subcellular localization of four OsANTH proteins that were preferentially expressed in mature pollen can be consistent with their role in endocytosis in the plasma membrane. Of them, OsANTH3 represented the highest expression in mature pollen. Functional characterization of using T-DNA insertional knockout and gene-edited mutants revealed that a mutation in decreased seed fertility by reducing the pollen germination percentage in rice. Thus, our study suggests OsANTH3-mediated endocytosis is important for rice pollen germination.
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http://dx.doi.org/10.3389/fpls.2021.609473DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8076639PMC
April 2021

Rice PIN Auxin Efflux Carriers Modulate the Nitrogen Response in a Changing Nitrogen Growth Environment.

Int J Mol Sci 2021 Mar 23;22(6). Epub 2021 Mar 23.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Auxins play an essential role in regulating plant growth and adaptation to abiotic stresses, such as nutrient stress. Our current understanding of auxins is based almost entirely on the results of research on the eudicot , however, the role of the rice PIN-FORMED (PIN) auxin efflux carriers in the regulation of the ammonium-dependent response remains elusive. Here, we analyzed the expression patterns in various organs/tissues and the ammonium-dependent response of rice -family genes ( genes) via qRT-PCR, and attempted to elucidate the relationship between nitrogen (N) utilization and auxin transporters. To investigate auxin distribution under ammonium-dependent response after N deficiency in rice roots, we used DR5::VENUS reporter lines that retained a highly active synthetic auxin response. Subsequently, we confirmed that ammonium supplementation reduced the DR5::VENUS signal compared with that observed in the N-deficient condition. These results are consistent with the decreased expression patterns of almost all genes in the presence of the ammonium-dependent response to N deficiency. Furthermore, the mutant showed an insensitive phenotype in the ammonium-dependent response to N deficiency and disturbances in the regulation of several N-assimilation genes. These molecular and physiological findings suggest that auxin is involved in the ammonium assimilation process of rice, which is a model crop plant.
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http://dx.doi.org/10.3390/ijms22063243DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8005180PMC
March 2021

Arachis hypogaea resveratrol synthase 3 alters the expression pattern of UDP-glycosyltransferase genes in developing rice seeds.

PLoS One 2021 14;16(1):e0245446. Epub 2021 Jan 14.

Department of Plant Science, Research Institute for Agriculture and Life Sciences, and Plant Genomics and Breeding Institute, Seoul National University, Seoul, Republic of Korea.

The resveratrol-producing rice (Oryza sativa L.) inbred lines, Iksan 515 (I.515) and Iksan 526 (I.526), developed by the expression of the groundnut (Arachis hypogaea) resveratrol synthase 3 (AhRS3) gene in the japonica rice cultivar Dongjin, accumulated both resveratrol and its glucoside, piceid, in seeds. Here, we investigated the effect of the AhRS3 transgene on the expression of endogenous piceid biosynthesis genes (UGTs) in the developing seeds of the resveratrol-producing rice inbred lines. Ultra-performance liquid chromatography (UPLC) analysis revealed that I.526 accumulates significantly higher resveratrol and piceid in seeds than those in I.515 seeds and, in I.526 seeds, the biosynthesis of resveratrol and piceid reached peak levels at 41 days after heading (DAH) and 20 DAH, respectively. Furthermore, RNA-seq analysis showed that the expression patterns of UGT genes differed significantly between the 20 DAH seeds of I.526 and those of Dongjin. Quantitative real-time PCR (RT-qPCR) analyses confirmed the data from RNA-seq analysis in seeds of Dongjin, I.515 and I.526, respectively, at 9 DAH, and in seeds of Dongjin and I.526, respectively, at 20 DAH. A total of 245 UGTs, classified into 31 UGT families, showed differential expression between Dongjin and I.526 seeds at 20 DAH. Of these, 43 UGTs showed more than 2-fold higher expression in I.526 seeds than in Dongjin seeds. In addition, the expression of resveratrol biosynthesis genes (PAL, C4H and 4CL) was also differentially expressed between Dongjin and I.526 developing seeds. Collectively, these data suggest that AhRS3 altered the expression pattern of UGT genes, and PAL, C4H and 4CL in developing rice seeds.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0245446PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7808588PMC
January 2021

Key Genes in the Melatonin Biosynthesis Pathway with Circadian Rhythm Are Associated with Various Abiotic Stresses.

Plants (Basel) 2021 Jan 9;10(1). Epub 2021 Jan 9.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Melatonin (N-acetyl-5-methoxytryptamine), a well-known animal hormone, is involved in several biological processes including circadian rhythm and the regulation of abiotic stress. A systematic understanding of the circadian regulation of melatonin biosynthesis-related genes has not been achieved in rice. In this study, key genes for all of the enzymes in the melatonin biosynthetic pathway that showed a peak of expression at night were identified by microarray data analysis and confirmed by qRT-PCR analysis. We further examined the expression patterns of the four genes under drought, salt, and cold stresses. The results showed that abiotic stresses, such as drought, salt, and cold, affected the expression patterns of melatonin biosynthetic genes. In addition, the circadian expression patterns of tryptophan decarboxylase (), tryptamine 5-hydroxylase (), and serotonin -acetyltransferase () genes in wild-type (WT) plants was damaged by the drought treatment under light and dark conditions. Conversely, -acetylserotonin -methyltransferase () retained the circadian rhythm. The expression of was down-regulated by the rice () mutation, suggesting the involvement of the melatonin biosynthetic pathway in the OsGI-mediated circadian regulation pathway. Taken together, our results provide clues to explain the relationship between circadian rhythms and abiotic stresses in the process of melatonin biosynthesis in rice.
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http://dx.doi.org/10.3390/plants10010129DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7827461PMC
January 2021

Phosphate-Starvation-Inducible S-Like RNase Genes in Rice Are Involved in Phosphate Source Recycling by RNA Decay.

Front Plant Sci 2020 30;11:585561. Epub 2020 Nov 30.

Graduate School of Biotechnology, Kyung Hee University, Yongin, South Korea.

The fine-tuning of inorganic phosphate (Pi) for enhanced use efficiency has long been a challenging subject in agriculture, particularly in regard to rice as a major crop plant. Among ribonucleases (RNases), the RNase T2 family is broadly distributed across kingdoms, but little has been known on its substrate specificity compared to RNase A and RNase T1 families. Class I and class II of the RNase T2 family are defined as the S-like RNase (RNS) family and have showed the connection to Pi recycling in Arabidopsis. In this study, we first carried out a phylogenetic analysis of eight rice and five Arabidopsis genes and identified mono-specific class I and dicot-specific class I RNS genes, suggesting the possibility of functional diversity between class I RNS family members in monocot and dicot species through evolution. We then compared the expression patterns of all genes in rice and Arabidopsis under normal and Pi-deficient conditions and further confirmed the expression patterns of rice genes via qRT-PCR analysis. Subsequently, we found that most of the genes were differentially regulated under Pi-deficient treatment. Association of Pi recycling by RNase activity in rice was confirmed by measuring total RNA concentration and ribonuclease activity of shoot and root samples under Pi-sufficient or Pi-deficient treatment during 21 days. The total RNA concentrations were decreased by < 60% in shoots and < 80% in roots under Pi starvation, respectively, while ribonuclease activity increased correspondingly. We further elucidate the signaling pathway of Pi starvation through upregulation of the genes. The 2-kb promoter region of all genes with inducible expression patterns under Pi deficiency contains a high frequency of P1BS cis-acting regulatory element (CRE) known as the OsPHR2 binding site, suggesting that the OsRNS family is likely to be controlled by OsPHR2. Finally, the dynamic transcriptional regulation of genes by overexpression of , mutant, and overexpression of lines involved in Pi signaling pathway suggests the molecular basis of family in Pi recycling via RNA decay under Pi starvation.
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http://dx.doi.org/10.3389/fpls.2020.585561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793952PMC
November 2020

OsPP2C09 Is a Bifunctional Regulator in Both ABA-Dependent and Independent Abiotic Stress Signaling Pathways.

Int J Mol Sci 2021 Jan 1;22(1). Epub 2021 Jan 1.

Division of Metabolic Engineering, National Institute of Agricultural Sciences, RDA, Jeonju-si 54874, Korea.

Clade A Type 2C protein phosphatases (PP2CAs) negatively regulate abscisic acid (ABA) signaling and have diverse functions in plant development and in response to various stresses. In this study, we showed that overexpression of the rice ABA receptor OsPYL/RCAR3 reduces the growth retardation observed in plants exposed to osmotic stress. By contrast, overexpression of the OsPYL/RCAR3-interacting protein OsPP2C09 rendered plant growth more sensitive to osmotic stress. We tested whether OsPP2CAs activate an ABA-independent signaling cascade by transfecting rice protoplasts with luciferase reporters containing the drought-responsive element (DRE) or ABA-responsive element (ABRE). We observed that OsPP2CAs activated gene expression via the cis-acting drought-responsive element. In agreement with this observation, transcriptome analysis of plants overexpressing OsPP2C09 indicated that OsPP2C09 induces the expression of genes whose promoters contain DREs. Further analysis showed that OsPP2C09 interacts with DRE-binding (DREB) transcription factors and activates reporters containing DRE. We conclude that, through activating DRE-containing promoters, OsPP2C09 positively regulates the drought response regulon and activates an ABA-independent signaling pathway.
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http://dx.doi.org/10.3390/ijms22010393DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7795834PMC
January 2021

GORI, encoding the WD40 domain protein, is required for pollen tube germination and elongation in rice.

Plant J 2021 Mar 21;105(6):1645-1664. Epub 2021 Jan 21.

Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin, 17104, Republic of Korea.

Successful delivery of sperm cells to the embryo sac in higher plants is mediated by pollen tube growth. The molecular mechanisms underlying pollen germination and tube growth in crop plants remain rather unclear, although these mechanisms are crucial to plant reproduction and seed formation. By screening pollen-specific gene mutants in rice (Oryza sativa), we identified a T-DNA insertional mutant of Germinating modulator of rice pollen (GORI) that showed a one-to-one segregation ratio for wild type (WT) to heterozygous. GORI encodes a seven-WD40-motif protein that is homologous to JINGUBANG/REN4 in Arabidopsis. GORI is specifically expressed in rice pollen, and its protein is localized in the nucleus, cytosol and plasma membrane. Furthermore, a homozygous mutant, gori-2, created through CRISPR-Cas9 clearly exhibited male sterility with disruption of pollen tube germination and elongation. The germinated pollen tube of gori-2 exhibited decreased actin filaments and altered pectin distribution. Transcriptome analysis revealed that 852 pollen-specific genes were downregulated in gori-2 compared with the WT, and Gene Ontology enrichment analysis indicated that these genes are strongly associated with cell wall modification and clathrin coat assembly. Based on the molecular features of GORI, phenotypical observation of the gori mutant and its interaction with endocytic proteins and Rac GTPase, we propose that GORI plays key roles in forming endo-/exocytosis complexes that could mediate pollen tube growth in rice.
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http://dx.doi.org/10.1111/tpj.15139DOI Listing
March 2021

Systematic Analysis of Cold Stress Response and Diurnal Rhythm Using Transcriptome Data in Rice Reveals the Molecular Networks Related to Various Biological Processes.

Int J Mol Sci 2020 Sep 19;21(18). Epub 2020 Sep 19.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Rice ( L.), a staple crop plant that is a major source of calories for approximately 50% of the human population, exhibits various physiological responses against temperature stress. These responses are known mechanisms of flexible adaptation through crosstalk with the intrinsic circadian clock. However, the molecular regulatory network underlining this crosstalk remains poorly understood. Therefore, we performed systematic transcriptome data analyses to identify the genes involved in both cold stress responses and diurnal rhythmic patterns. Here, we first identified cold-regulated genes and then identified diurnal rhythmic genes from those (119 cold-upregulated and 346 cold-downregulated genes). We defined cold-responsive diurnal rhythmic genes as CD genes. We further analyzed the functional features of these CD genes through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses and performed a literature search to identify functionally characterized CD genes. Subsequently, we found that light-harvesting complex proteins involved in photosynthesis strongly associate with the crosstalk. Furthermore, we constructed a protein-protein interaction network encompassing four hub genes and analyzed the roles of the gene in regulating crosstalk with mutants. We predict that these findings will provide new insights in understanding the environmental stress response of crop plants against climate change.
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http://dx.doi.org/10.3390/ijms21186872DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7554834PMC
September 2020

An Abiotic Stress Responsive U-Box E3 Ubiquitin Ligase Is Involved in OsGI-Mediating Diurnal Rhythm Regulating Mechanism.

Plants (Basel) 2020 Aug 20;9(9). Epub 2020 Aug 20.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

The plant U-box (PUB) protein is the E3 ligase that plays roles in the degradation or post-translational modification of target proteins. In rice, 77 U-box proteins were identified and divided into eight classes according to the domain configuration. We performed a phylogenomic analysis by integrating microarray expression data under abiotic stress to the phylogenetic tree context. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) expression analyses identified that eight, twelve, and eight family genes are associated with responses to drought, salinity, and cold stress, respectively. In total, 16 genes showed increased expression in response to three abiotic stresses. Among them, the expression of in class II and , , and in class III increased in all three abiotic stresses, indicating their involvement in multiple abiotic stress regulation. In addition, we identified the circadian rhythmic expression for three out of 16 genes responding to abiotic stress through meta-microarray expression data analysis. Among them, OsPUB4 is predicted to be involved in the rice GIGANTEA (OsGI)-mediating diurnal rhythm regulating mechanism. In the last, we constructed predicted protein-protein interaction networks associated with OsPUB4 and OsGI. Our analysis provides essential information to improve environmental stress tolerance mediated by the PUB family members in rice.
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http://dx.doi.org/10.3390/plants9091071DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7569774PMC
August 2020

A Revolution toward Gene-Editing Technology and Its Application to Crop Improvement.

Int J Mol Sci 2020 Aug 7;21(16). Epub 2020 Aug 7.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Genome editing is a relevant, versatile, and preferred tool for crop improvement, as well as for functional genomics. In this review, we summarize the advances in gene-editing techniques, such as zinc-finger nucleases (ZFNs), transcription activator-like (TAL) effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR) associated with the Cas9 and Cpf1 proteins. These tools support great opportunities for the future development of plant science and rapid remodeling of crops. Furthermore, we discuss the brief history of each tool and provide their comparison and different applications. Among the various genome-editing tools, CRISPR has become the most popular; hence, it is discussed in the greatest detail. CRISPR has helped clarify the genomic structure and its role in plants: For example, the transcriptional control of Cas9 and Cpf1, genetic locus monitoring, the mechanism and control of promoter activity, and the alteration and detection of epigenetic behavior between single-nucleotide polymorphisms (SNPs) investigated based on genetic traits and related genome-wide studies. The present review describes how CRISPR/Cas9 systems can play a valuable role in the characterization of the genomic rearrangement and plant gene functions, as well as the improvement of the important traits of field crops with the greatest precision. In addition, the speed editing strategy of gene-family members was introduced to accelerate the applications of gene-editing systems to crop improvement. For this, the CRISPR technology has a valuable advantage that particularly holds the scientist's mind, as it allows genome editing in multiple biological systems.
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http://dx.doi.org/10.3390/ijms21165665DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7461041PMC
August 2020

High-throughput phenotyping platform for analyzing drought tolerance in rice.

Planta 2020 Aug 10;252(3):38. Epub 2020 Aug 10.

The National Institute of Agricultural Sciences, 370 Nongsaengmyeong-ro, Wansan-gu, Jeonju-si, Jeollabuk-do, Republic of Korea.

Main Conclusion: A new imaging platform was constructed to analyze drought-tolerant traits of rice. Rice was used to quantify drought phenotypes through image-based parameters and analyzing tools. Climate change has increased the frequency and severity of drought, which limits crop production worldwide. Developing new cultivars with increased drought tolerance and short breeding cycles is critical. However, achieving this goal requires phenotyping a large number of breeding populations in a short time and in an accurate manner. Novel cutting-edge technologies such as those based on remote sensors are being applied to solve this problem. In this study, new technologies were applied to obtain and analyze imaging data and establish efficient screening platforms for drought tolerance in rice using the drought-tolerant mutant osphyb. Red-Green-Blue images were used to predict plant area, color, and compactness. Near-infrared imaging was used to determine the water content of rice, infrared was used to assess plant temperature, and fluorescence was used to examine photosynthesis efficiency. DroughtSpotter technology was used to determine water use efficiency, plant water loss rate, and transpiration rate. The results indicate that these methods can detect the difference between tolerant and susceptible plants, suggesting their value as high-throughput phenotyping methods for short breeding cycles as well as for functional genetic studies of tolerance to drought stress.
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http://dx.doi.org/10.1007/s00425-020-03436-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7417419PMC
August 2020

Global Analysis of Cereal microProteins Suggests Diverse Roles in Crop Development and Environmental Adaptation.

G3 (Bethesda) 2020 10 5;10(10):3709-3717. Epub 2020 Oct 5.

Copenhagen Plant Science Centre, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark

MicroProteins are a class of small single-domain proteins that post-translationally regulate larger multidomain proteins from which they evolved or which they relate to. They disrupt the normal function of their targets by forming microProtein-target heterodimers through compatible protein-protein interaction (PPI) domains. Recent studies confirm the significance of microProteins in the fine-tuning of plant developmental processes such as shoot apical meristem maintenance and flowering time regulation. While there are a number of well-characterized microProteins in , studies from more complex plant genomes are still missing. We have previously developed miPFinder, a software for identifying microProteins from annotated genomes. Here we present an improved version where we have updated the algorithm to increase its accuracy and speed, and used it to analyze five cereal crop genomes - wheat, rice, barley, maize and sorghum. We found 20,064 potential microProteins from a total of 258,029 proteins in these five organisms, of which approximately 2000 are high-confidence, , likely to function as actual microProteins. Gene ontology analysis of these 2000 microProtein candidates revealed their roles in stress, light and growth responses, hormone signaling and transcriptional regulation. Using a recently developed rice gene co-expression database, we analyzed 347 potential rice microProteins that are also conserved in other cereal crops and found over 50 of these rice microProteins to be co-regulated with their identified interaction partners. Overall, our study reveals a rich source of biotechnologically interesting small proteins that regulate fundamental plant processes such a growth and stress response that could be utilized in crop bioengineering.
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http://dx.doi.org/10.1534/g3.120.400794DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7534434PMC
October 2020

First Steps in the Successful Fertilization of Rice and : Pollen Longevity, Adhesion and Hydration.

Plants (Basel) 2020 Jul 29;9(8). Epub 2020 Jul 29.

Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Understanding the behavior of pollen during pollination is important for food security in the future. The elucidation of pollen development and growth regulation largely relies on the study of the dicotyledonous model plant . However, rice () pollen exhibits different characteristics to that of . The latter undergoes programmed dehydration and withstands adverse environmental conditions, whereas rice pollen is sensitive to desiccation. Moreover, the short longevity of rice pollen significantly hampers hybrid seed production. Although the "omics" data for mature rice pollen have been accumulated, few genes that control pollination and pollen hydration have been identified. Therefore, to facilitate future studies, it is necessary to summarize the developmental processes involved in pollen production in rice and to consolidate the underlying mechanisms discovered in previous studies. In this review, we describe the pollen developmental processes and introduce gametophytic mutants, which form defective pollen in and rice. In addition, we discuss the perspectives on the research on pollen longevity, adhesion and hydration.
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http://dx.doi.org/10.3390/plants9080956DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7465243PMC
July 2020

CAFRI-Rice: CRISPR applicable functional redundancy inspector to accelerate functional genomics in rice.

Plant J 2020 10 31;104(2):532-545. Epub 2020 Aug 31.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin, 17104, South Korea.

Rice (Oryza sativa L.) is a staple crop with agricultural traits that have been intensively investigated. However, despite the variety of mutant population and multi-omics data that have been generated, rice functional genomic research has been bottlenecked due to the functional redundancy in the genome. This phenomenon has masked the phenotypes of knockout mutants by functional compensation and redundancy. Here, we present an intuitive tool, CRISPR applicable functional redundancy inspector to accelerate functional genomics in rice (CAFRI-Rice; cafri-rice.khu.ac.kr). To create this tool, we generated a phylogenetic heatmap that can estimate the similarity between protein sequences and expression patterns, based on 2,617 phylogenetic trees and eight tissue RNA-sequencing datasets. In this study, 33,483 genes were sorted into 2,617 families, and about 24,980 genes were tested for functional redundancy using a phylogenetic heatmap approach. It was predicted that 7,075 genes would have functional redundancy, according to the threshold value validated by an analysis of 111 known genes functionally characterized using knockout mutants and 5,170 duplicated genes. In addition, our analysis demonstrated that an anther/pollen-preferred gene cluster has more functional redundancy than other clusters. Finally, we showed the usefulness of the CAFRI-Rice-based approach by overcoming the functional redundancy between two root-preferred genes via loss-of-function analyses as well as confirming the functional dominancy of three genes through a literature search. This CAFRI-Rice-based target selection for CRISPR/Cas9-mediated mutagenesis will not only accelerate functional genomic studies in rice but can also be straightforwardly expanded to other plant species.
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http://dx.doi.org/10.1111/tpj.14926DOI Listing
October 2020

Physiological Importance of Pectin Modifying Genes During Rice Pollen Development.

Int J Mol Sci 2020 Jul 8;21(14). Epub 2020 Jul 8.

Department of Plant & Environmental New Resources, College of Life Sciences, Kyung Hee University, Yongin 17104, Korea.

Although cell wall dynamics, particularly modification of homogalacturonan (HGA, a major component of pectin) during pollen tube growth, have been extensively studied in dicot plants, little is known about how modification of the pollen tube cell wall regulates growth in monocot plants. In this study, we assessed the role of HGA modification during elongation of the rice pollen tube by adding a pectin methylesterase (PME) enzyme or a PME-inhibiting catechin extract (Polyphenon 60) to in vitro germination medium. Both treatments led to a severe decrease in the pollen germination rate and elongation. Furthermore, using monoclonal antibodies toward methyl-esterified and de-esterified HGA epitopes, it was found that exogenous treatment of PME and Polyphenon 60 resulted in the disruption of the distribution patterns of low- and high-methylesterified pectins upon pollen germination and during pollen tube elongation. Eleven PMEs and 13 PME inhibitors (PMEIs) were identified by publicly available transcriptome datasets and their specific expression was validated by qRT-PCR. Enzyme activity assays and subcellular localization using a heterologous expression system in tobacco leaves demonstrated that some of the pollen-specific PMEs and PMEIs possessed distinct enzymatic activities and targeted either the cell wall or other compartments. Taken together, our findings are the first line of evidence showing the essentiality of HGA methyl-esterification status during the germination and elongation of pollen tubes in rice, which is primarily governed by the fine-tuning of PME and PMEI activities.
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http://dx.doi.org/10.3390/ijms21144840DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7402328PMC
July 2020

Re-Analysis of 16S Amplicon Sequencing Data Reveals Soil Microbial Population Shifts in Rice Fields under Drought Condition.

Rice (N Y) 2020 Jul 2;13(1):44. Epub 2020 Jul 2.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin, 17104, South Korea.

Rice (Oryza sativa. L) has been intensively studied to ensure a stable global supply of this commodity in the face of rapid global climate change. A critical factor that decreases crop yield is drought, which has been analyzed in various ways through many researches. Microbiome-based studies of rice investigate the symbiosis between rice and bacteria, which has been proposed as a way to overcome problems caused by drought. Several rice-associated metagenomic profiles obtained under drought conditions have been reported since the advent of next generation sequencing (NGS) technology. To elucidate the future diversity of plants and microorganisms and to promote sustainable agriculture, we reanalyzed 64 of the publicly available 16S amplicon sequencing data produced under drought condition. In the process of integrating data sets, however, we found an inconsistency that serves as a bottleneck for microbiome-based sustainability research. While this report provides clues about the composition of the microbiome under the drought conditions, the results are affected by differences in the location of the experiments, sampling conditions, and analysis protocols. Re-analysis of amplicon sequencing data of the soil microbiome in rice fields suggests that microbial composition shifts in response to drought condition and the presence of plants. Among the bacteria involved, the phylum Proteobacteria appears to play the most important role in the survival of rice under drought condition.
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http://dx.doi.org/10.1186/s12284-020-00403-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7332601PMC
July 2020

Homeobox transcription factor OsZHD2 promotes root meristem activity in rice by inducing ethylene biosynthesis.

J Exp Bot 2020 09;71(18):5348-5364

Crop Biotech Institute and Graduate School of Biotechnology, Kyung Hee University, Yongin, Korea.

Root meristem activity is the most critical process influencing root development. Although several factors that regulate meristem activity have been identified in rice, studies on the enhancement of meristem activity in roots are limited. We identified a T-DNA activation tagging line of a zinc-finger homeobox gene, OsZHD2, which has longer seminal and lateral roots due to increased meristem activity. The phenotypes were confirmed in transgenic plants overexpressing OsZHD2. In addition, the overexpressing plants showed enhanced grain yield under low nutrient and paddy field conditions. OsZHD2 was preferentially expressed in the shoot apical meristem and root tips. Transcriptome analyses and quantitative real-time PCR experiments on roots from the activation tagging line and the wild type showed that genes for ethylene biosynthesis were up-regulated in the activation line. Ethylene levels were higher in the activation lines compared with the wild type. ChIP assay results suggested that OsZHD2 induces ethylene biosynthesis by controlling ACS5 directly. Treatment with ACC (1-aminocyclopropane-1-carboxylic acid), an ethylene precursor, induced the expression of the DR5 reporter at the root tip and stele, whereas treatment with an ethylene biosynthesis inhibitor, AVG (aminoethoxyvinylglycine), decreased that expression in both the wild type and the OsZHD2 overexpression line. These observations suggest that OsZHD2 enhances root meristem activity by influencing ethylene biosynthesis and, in turn, auxin.
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http://dx.doi.org/10.1093/jxb/eraa209DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7501826PMC
September 2020

Overexpression of a novel cytochrome P450 monooxygenase gene, CYP704B1, from Panax ginseng increase biomass of reproductive tissues in transgenic Arabidopsis.

Mol Biol Rep 2020 Jun 19;47(6):4507-4518. Epub 2020 May 19.

Graduate School of Biotechnology and Department of Oriental Medicinal Biotechnology, College of Life Science, Kyung Hee University, Yongin, 446-701, Korea.

Cytochrome P450 monooxygenase 704B (CYP704B), a member of the CYP86 clan, was found to be needed in Arabidopsis and rice to biosynthesize precursors of sporopollenin through oxidizing fatty acids. In the present study, we cloned and characterized a CYP704B gene in Panax ginseng, named PgCYP704B1. It shared high sequence identity (98-99%) with CYP704 of Arabidopsis, Theobroma cacao, and Morus notabilis. The phylogenetic comparison of ginseng and higher plants between the members of CYP86 clan revealed that ginseng CYP704 was categorized as a group of CYP704B with dicot plants. The expression of PgCYP704B1 is low in the stem, leaf, and fruit, and high in flower buds, particularly detected in the young gametic cell and tapetum layer of the developing anther. Arabidopsis plants overexpressing PgCYP704B1 improved plant biomass such as plant height, siliques and seed number and size. A cytological observation by transverse and longitudinal semi-thin sections of the siliques cuticles revealed that the cell length increased. Furthermore a chemical analysis showed that PgCYP704B1ox lines increased their cutin monomers contents in the siliques. Our results suggest that PgCYP704B1 has a conserved role during male reproduction for fatty acid biosynthesis and its overexpression increases cutin monomers in siliques that eventually could be used for seed production.
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http://dx.doi.org/10.1007/s11033-020-05528-xDOI Listing
June 2020

Negatively Regulates Internode Elongation and Plant Height by Modulating GA Homeostasis in Rice.

Plants (Basel) 2020 Apr 23;9(4). Epub 2020 Apr 23.

School of Applied Biosciences, Kyungpook National University, Daegu 41566, Korea.

Internode elongation is one of the key agronomic traits determining a plant's height and biomass. However, our understanding of the molecular mechanisms controlling internode elongation is still limited in crop plant species. Here, we report the functional identification of an atypical basic helix-loop-helix transcription factor () through gain-of-function studies using overexpression () and activation tagging () lines of rice. The expression of was significantly increased in the line. The phenotype of showed semi-dwarfism due to deficient elongation of the first internode and poor panicle exsertion. Transgenic lines overexpressing confirmed the phenotype of the line. Exogenous gibberellic acid (GA) treatment recovered the semi-dwarf phenotype of plants at the seedling stage. In addition, quantitative expression analysis of genes involving in GA biosynthetic and signaling pathway revealed that the transcripts of rice and ( and ) encoding the GA biosynthetic enzyme were significantly downregulated in and lines. Yeast two-hybrid and localization assays showed that the OsbHLH073 protein is a nuclear localized-transcriptional activator. We report that participates in regulating plant height, internode elongation, and panicle exsertion by regulating GA biosynthesis associated with the and genes.
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http://dx.doi.org/10.3390/plants9040547DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7238965PMC
April 2020

Conventional and Molecular Techniques from Simple Breeding to Speed Breeding in Crop Plants: Recent Advances and Future Outlook.

Int J Mol Sci 2020 Apr 8;21(7). Epub 2020 Apr 8.

Institute of Crop Science and Zhejiang Key Laboratory of Crop Germplasm, Zhejiang University, Hangzhou 310058, China.

In most crop breeding programs, the rate of yield increment is insufficient to cope with the increased food demand caused by a rapidly expanding global population. In plant breeding, the development of improved crop varieties is limited by the very long crop duration. Given the many phases of crossing, selection, and testing involved in the production of new plant varieties, it can take one or two decades to create a new cultivar. One possible way of alleviating food scarcity problems and increasing food security is to develop improved plant varieties rapidly. Traditional farming methods practiced since quite some time have decreased the genetic variability of crops. To improve agronomic traits associated with yield, quality, and resistance to biotic and abiotic stresses in crop plants, several conventional and molecular approaches have been used, including genetic selection, mutagenic breeding, somaclonal variations, whole-genome sequence-based approaches, physical maps, and functional genomic tools. However, recent advances in genome editing technology using programmable nucleases, clustered regularly interspaced short palindromic repeats (CRISPR), and CRISPR-associated (Cas) proteins have opened the door to a new plant breeding era. Therefore, to increase the efficiency of crop breeding, plant breeders and researchers around the world are using novel strategies such as speed breeding, genome editing tools, and high-throughput phenotyping. In this review, we summarize recent findings on several aspects of crop breeding to describe the evolution of plant breeding practices, from traditional to modern speed breeding combined with genome editing tools, which aim to produce crop generations with desired traits annually.
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http://dx.doi.org/10.3390/ijms21072590DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7177917PMC
April 2020

Comprehensive phylogenomic analysis of ERF genes in sorghum provides clues to the evolution of gene functions and redundancy among gene family members.

3 Biotech 2020 Mar 25;10(3):139. Epub 2020 Feb 25.

1Crop Genetics & Informatics Group, School of Biotechnology, Jawaharlal Nehru University, New Mehrauli Road, New Delhi, 110067 India.

APETALA2/Ethylene-Responsive transcription factors (AP2/ERF), with their multifunctional roles in plant development, hormone signaling and stress tolerance, are important candidates for engineering crop plants. Here, we report identification and analysis of gene structure, phylogenetic distribution, expression, chromosomal localization and -acting promoter analysis of AP2/ERF genes in the C4 crop plant sorghum. We identified 158 ERF genes in sorghum with 52 of them encoding dehydration-responsive binding elements (DREB) while 106 code for ERF subfamily proteins. Phylogenetic analysis organized sorghum ERF proteins into 11 distinct groups exhibiting clade-specific expansion. About 68% ERF genes have paralogs indicating gene duplications as major cause of expansion of ERF family in sorghum. Analysis of spatiotemporal expression patterns using publicly available data revealed their tissue/genotype-preferential accumulation. In addition, 40 ERF genes exhibited differential accumulation in response to heat and/or drought stress. About 25% of the segmental gene pairs and eleven tandem duplicated genes exhibited high correlation (> 0.7) in their expression patterns indicating genetic redundancy. Comparative phylogenomic analysis of sorghum ERFs with 74 genetically characterized ERF genes from other plant species provided significant clues to sorghum ERF functions. Overall data generated here provides an overview of evolutionary relationship among ERF gene family members in sorghum and with respect to previously characterized ERF genes from other plant species. This information will be instrumental in initiating functional genomic studies of ERF candidates in sorghum.
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http://dx.doi.org/10.1007/s13205-020-2120-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7042439PMC
March 2020

Pathogenesis strategies and regulation of ginsenosides by two species of in : power of speciation.

J Ginseng Res 2020 Mar 19;44(2):332-340. Epub 2019 Feb 19.

Graduate School of Biotechnology, College of Life Science, Kyung Hee University, Yongin, Republic of Korea.

Background: The valuable medicinal plant has high pharmaceutical efficacy because it produces ginsenosides. However, its yields decline because of a root-rot disease caused by . Because species within showed variable aggressiveness by altering ginsenoside concentrations in inoculated plants, we investigated how such infections might regulate the biosynthesis of ginsenosides and their related signaling molecules.

Methods: Two-year-old ginseng seedlings were treated with and Roots from infected and pathogen-free plants were harvested at 4 and 16 days after inoculation. We then examined levels or/and expression of genes of ginsenosides, salicylic acid (SA), jasmonic acid (JA), and reactive oxygen species (ROS). We also checked the susceptibility of those pathogens to ROS.

Results: Ginsenoside biosynthesis was significantly suppressed and increased in response to infection by and , respectively. Regulation of JA was significantly higher in -infected roots, while levels of SA and ROS were significantly higher in -infected roots. Catalase activity was significantly higher in -infected roots followed in order by mock roots and those infected by . Moreover, was resistant to ROS compared with .

Conclusion: Infection by the weakly aggressive led to the upregulation of ginsenoside production and biosynthesis, probably because only a low level of ROS was induced. In contrast, the more aggressive suppressed ginsenoside biosynthesis, probably because of higher ROS levels and subsequent induction of programmed cell death pathways. Furthermore, may have increased its virulence by resisting the cytotoxicity of ROS.
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http://dx.doi.org/10.1016/j.jgr.2019.02.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7031752PMC
March 2020

Genome-wide analysis of RopGEF gene family to identify genes contributing to pollen tube growth in rice (Oryza sativa).

BMC Plant Biol 2020 Mar 4;20(1):95. Epub 2020 Mar 4.

Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin, 17104, South Korea.

Background: In plants, the key roles played by RopGEF-mediated ROP signaling in diverse processes, including polar tip growth, have been identified. Despite their important roles in reproduction, a comprehensive analysis of RopGEF members has not yet been performed in rice (Oryza sativa). To determine whether RopGEF regulators are involved in rice pollen tube growth, we performed genome-wide analysis of this family in rice.

Results: Phylogenomic and meta-expression analysis of eleven RopGEFs in rice showed that four genes were preferentially expressed in mature pollen. These four genes contain the plant-specific Rop nucleotide exchanger (PRONE) domain and possible phosphorylated residues, suggesting a conserved role in polar tip growth with Arabidopsis thaliana. In subcellular localization analysis of the four RopGEFs through tobacco (Nicotiana benthamiana) infiltration, four proteins were predominantly identified in plasma membrane. Moreover, double mutants of RopGEF2/8 exhibited reduced pollen germination, causing partial male sterility. These genes possess unique cis-acting elements in their promoters compared with the other RopGEF genes.

Conclusions: In this study, four RopGEF genes were identified as pollen-specific gene in eleven members of rice, and the expression pattern, promoter analysis, and evolutionary relationship of the RopGEF family were studied compared with Arabidopsis. Our study indicated that four RopGEF genes might function during pollen germination in distinct subcellular localization. Our study could provide valuable information on the functional study of RopGEF in rice.
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http://dx.doi.org/10.1186/s12870-020-2298-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7057574PMC
March 2020

Fast Track to Discover Novel Promoters in Rice.

Plants (Basel) 2020 Jan 18;9(1). Epub 2020 Jan 18.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Promoters are key components for the application of biotechnological techniques in crop plants. Reporter genes such as or have been used to test the activity of promoters for diverse applications. A huge number of T-DNAs carrying promoterless near their right borders have been inserted into the rice genome, and 105,739 flanking sequence tags from rice lines with this T-DNA insertion have been identified, establishing potential promoter trap lines for 20,899 out of 55,986 genes in the rice genome. Anatomical meta-expression data and information on abiotic stress related to these promoter trap lines enable us to quickly identify new promoters associated with various expression patterns. In the present report, we introduce a strategy to identify new promoters in a very short period of time using a combination of meta-expression analysis and promoter trap lines.
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http://dx.doi.org/10.3390/plants9010125DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7020180PMC
January 2020

Rice Senescence-Induced Receptor-Like Kinase () Is Involved in Phytohormone-Mediated Chlorophyll Degradation.

Int J Mol Sci 2019 Dec 30;21(1). Epub 2019 Dec 30.

Department of Plant Life and Environmental Science, Hankyong National University, 327, Jungangro, Anseong-si, Gyeonggi-do 17579, Korea.

Chlorophyll breakdown is a vital catabolic process of leaf senescence as it allows the recycling of nitrogen and other nutrients. In the present study, we isolated rice senescence-induced receptor-like kinase (), whose transcription was upregulated in senescing rice leaves. The detached leaves of mutant () contained more green pigment than those of the wild type (WT) during dark-induced senescence (DIS). HPLC and immunoblot assay revealed that degradation of chlorophyll and photosystem II proteins was repressed in during DIS. Furthermore, ultrastructural analysis revealed that leaves maintained the chloroplast structure with intact grana stacks during dark incubation; however, the retained green color and preserved chloroplast structures of did not enhance the photosynthetic competence during age-dependent senescence in autumn. In , the panicles per plant was increased and the spikelets per panicle were reduced, resulting in similar grain productivity between WT and . By transcriptome analysis using RNA sequencing, genes related to phytohormone, senescence, and chlorophyll biogenesis were significantly altered in compared to those in WT during DIS. Collectively, our findings indicate that may degrade chlorophyll by participating in a phytohormone-mediated pathway.
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http://dx.doi.org/10.3390/ijms21010260DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6982081PMC
December 2019

PERSISTENT TAPETAL CELL2 Is Required for Normal Tapetal Programmed Cell Death and Pollen Wall Patterning.

Plant Physiol 2020 02 26;182(2):962-976. Epub 2019 Nov 26.

Joint International Research Laboratory of Metabolic and Developmental Sciences, Shanghai Jiao Tong University-University of Adelaide Joint Centre for Agriculture and Health, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China

The timely programmed cell death (PCD) of the tapetum, the innermost somatic anther cell layer in flowering plants, is critical for pollen development, including the deposition and patterning of the pollen wall. Although several genes involved in tapetal PCD and pollen wall development have been characterized, the underlying regulatory mechanism remains elusive. Here we report that (), which encodes an AT-hook nuclear localized protein in rice (), is required for normal tapetal PCD and pollen wall development. The mutant showed persistent tapetal cells and abnormal pollen wall patterning including absent nexine, collapsed bacula, and disordered tectum. The defective tapetal PCD phenotype of was similar to that of a PCD delayed mutant, , in rice, while the abnormal pollen wall patterning resembled that of a pollen wall defective mutant, , in Arabidopsis (). Levels of anther cutin monomers in anthers were significantly reduced, as was expression of a series of lipid biosynthetic genes. PTC2 transcript and protein were shown to be present in the anther after meiosis, consistent with the observed phenotype. Based on these data, we propose a model explaining how PTC2 affects anther and pollen development. The characterization of PTC2 in tapetal PCD and pollen wall patterning expands our understanding of the regulatory network of male reproductive development in rice and will aid future breeding approaches.
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http://dx.doi.org/10.1104/pp.19.00688DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6997677PMC
February 2020

Genome-Wide Transcriptome Analysis of Rice Seedlings after Seed Dressing with DCY84 and Silicon.

Int J Mol Sci 2019 Nov 23;20(23). Epub 2019 Nov 23.

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin 17104, Korea.

Plant-growth-promoting bacteria (PGPB) are beneficial microorganisms that can also protect against disease and environmental stress. Silicon (Si) is the second most abundant element in soil, and is known to increase plant growth, grain yield, resistance to biotic stress, and tolerance to abiotic stress. Combined treatment of PGPB and Si has been shown to further enhance plant growth and crop yield. To determine the global effects of the PGPB and Si on rice growth, we compared rice plants treated with DCY84 (DCY84) and Si with untreated rice. To identify the genes that respond to DCY84+Si treatment in rice, we performed an RNA-Seq transcriptome analysis by sampling treated and untreated roots on a weekly basis for three weeks. Overall, 576 genes were upregulated, and 394 genes were downregulated in treated roots, using threshold fold-changes of at least 2 (log) and -values < 0.05. Gene ontology analysis showed that phenylpropanoids and the L-phenylalanine metabolic process were prominent in the upregulated genes. In a metabolic overview analysis using the MapMan toolkit, pathways involving phenylpropanoids and ethylene were strongly associated with upregulated genes. The functions of seven upregulated genes were identified as being associated with drought stress through a literature search, and a stress experiment confirmed that plants treated with DCY84+Si exhibited greater drought tolerance than the untreated control plants. Furthermore, the predicted protein-protein interaction network analysis associated with DCY84+ Si suggests mechanisms underlying growth promotion and stress tolerance.
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http://dx.doi.org/10.3390/ijms20235883DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6928808PMC
November 2019

Phenylalanine ammonia-lyase family is closely associated with response to phosphate deficiency in rice.

Genes Genomics 2020 01 17;42(1):67-76. Epub 2019 Nov 17.

Graduate School of Biotechnology & Crop Biotechnology Institute, Kyung Hee University, Yongin, 17104, South Korea.

Background: Phenylalanine ammonia-lyase (PAL) catalyzes the first step in the biosynthetic phenylpropanoid pathway (PPP) via deamination of phenylalanine to trans-cinnamic acid, a precursor for the lignin and flavonoid biosynthetic pathways. Although its role is well-established in various plants, the functional significance of PAL genes in rice remains poorly understood.

Objective: This study aims to find out the global feature of rice PAL genes associated with phosphate use efficiency.

Methods: To identify the biological functions of individual rice PAL genes, we performed meta-expression profiling analysis based on phylogenomics of rice PAL genes and confirmed the expression patterns using Quantitative real-time PCR (qPCR).

Results: We identified nine genes that were remarkably up-regulated during long-term phosphate (Pi) starvation and recovery processes through RNA-Seq data analysis. Expression patterns of the nine rice PAL genes under Pi starvation were further confirmed by qPCR, indicating that the function of PAL genes is strongly associated with Pi starvation response in rice.

Conclusion: Our study reports the functional significance of rice PAL genes involved in adaptation to low Pi growth conditions and provides useful information to improve Pi use efficiency in crop plant.
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http://dx.doi.org/10.1007/s13258-019-00879-7DOI Listing
January 2020

Rice Genome-Scale Network Integration Reveals Transcriptional Regulators of Grass Cell Wall Synthesis.

Front Plant Sci 2019 18;10:1275. Epub 2019 Oct 18.

Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, United States.

Grasses have evolved distinct cell wall composition and patterning relative to dicotyledonous plants. However, despite the importance of this plant family, transcriptional regulation of its cell wall biosynthesis is poorly understood. To identify grass cell wall-associated transcription factors, we constructed the Rice Combined mutual Ranked Network (RCRN). The RCRN covers >90% of annotated rice () genes, is high quality, and includes most grass-specific cell wall genes, such as mixed-linkage glucan synthases and hydroxycinnamoyl acyltransferases. Comparing the RCRN and an equivalent network suggests that grass orthologs of most genetically verified eudicot cell wall regulators also control this process in grasses, but some transcription factors vary significantly in network connectivity between these divergent species. Reverse genetics, yeast-one-hybrid, and protoplast-based assays reveal that OsMYB61a activates a grass-specific acyltransferase promoter, which confirms network predictions and supports grass-specific cell wall synthesis genes being incorporated into conserved regulatory circuits. In addition, 10 of 15 tested transcription factors, including six novel Wall-Associated regulators (WAP1, WACH1, WAHL1, WADH1, OsMYB13a, and OsMYB13b), alter abundance of cell wall-related transcripts when transiently expressed. The results highlight the quality of the RCRN for examining rice biology, provide insight into the evolution of cell wall regulation, and identify network nodes and edges that are possible leads for improving cell wall composition.
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http://dx.doi.org/10.3389/fpls.2019.01275DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6813959PMC
October 2019

Deficiency of rice hexokinase HXK5 impairs synthesis and utilization of starch in pollen grains and causes male sterility.

J Exp Bot 2020 01;71(1):116-125

Graduate School of Biotechnology & Crop Biotech Institute, Kyung Hee University, Yongin, Korea.

There is little known about the function of rice hexokinases (HXKs) in planta. We characterized hxk5-1, a Tos17 mutant of OsHXK5 that is up-regulated in maturing pollen, a stage when starch accumulates. Progeny analysis of self-pollinated heterozygotes of hxk5-1 and reciprocal crosses between the wild-type and heterozygotes revealed that loss of HXK5 causes male sterility. Homozygous hxk5-1, produced via anther culture, and additional homozygous hxk5-2, hxk5-3 and hxk5-4 lines created by CRISPR/Cas9 confirmed the male-sterile phenotype. In vitro pollen germination ability and in vivo pollen tube growth rate were significantly reduced in the hxk5 mutant pollen. Biochemical analysis of anthers with the mutant pollen revealed significantly reduced hexokinase activity and starch content, although they were sufficient to produce some viable seed. However, the mutant pollen was unable to compete successfully against wild-type pollen. Expression of the catalytically inactive OsHXK5-G113D did not rescue the hxk5 male-sterile phenotype, indicating that its catalytic function was responsible for pollen fertility, rather than its role in sugar sensing and signaling. Our results demonstrate that OsHXK5 contributes to a large portion of the hexokinase activity necessary for the starch utilization pathway during pollen germination and tube growth, as well as for starch biosynthesis during pollen maturation.
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http://dx.doi.org/10.1093/jxb/erz436DOI Listing
January 2020