Publications by authors named "Mattias Holmlund"

5 Publications

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Organic nitrogen nutrition: LHT1.2 protein from hybrid aspen (Populus tremula L. x tremuloides Michx) is a functional amino acid transporter and a homolog of Arabidopsis LHT1.

Tree Physiol 2021 Feb 25. Epub 2021 Feb 25.

Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, 90183 Umeå, Sweden.

The contribution of amino acids (AAs) to soil nitrogen (N) fluxes is higher than previously thought. The fact that AA uptake is pivotal for N nutrition in boreal ecosystems highlights plant AA transporters as key components of the N cycle. At the same time, very little is known about AA transport and respective transporters in trees. Tree genomes may contain thirteen or more genes encoding the LYSINE HISTIDINE TRANSPORTER (LHT) family proteins, and this complicates the study of their significance for tree N use efficiency. With the strategy of obtaining a tool to study N use efficiency, our aim was to identify and characterize a relevant AA transporter in hybrid aspen (Populus tremula L. x tremuloides Michx.). We identified PtrLHT1.2, the closest homolog of Arabidopsis thaliana AtLHT1, which is expressed in leaves, stems and roots. Complementation of a yeast AA uptake mutant verified the function of PtrLHT1.2 as an AA transporter. Furthermore, PtrLHT1.2 was able to fully complement the phenotypes of the Arabidopsis AA uptake mutant lht1 aap5, including early leaf senescence-like phenotype, reduced growth, decreased plant N levels and reduced root AA uptake. AA uptake studies finally showed that PtrLHT1.2 is a high affinity transporter for neutral and acidic AAs. Thus, we identified a functional AtLHT1 homolog in hybrid aspen, which harbors the potential to enhance overall plant N levels and hence increase biomass production. This finding provides a valuable tool for N nutrition studies in trees and opens new avenues to optimizing tree N use efficiency.
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http://dx.doi.org/10.1093/treephys/tpab029DOI Listing
February 2021

LEAFY activity is post-transcriptionally regulated by BLADE ON PETIOLE2 and CULLIN3 in Arabidopsis.

New Phytol 2018 10 11;220(2):579-592. Epub 2018 Jul 11.

Univ. Grenoble Alpes, CNRS, CEA, INRA, BIG-LPCV, 38054, Grenoble Cedex 9, France.

The Arabidopsis LEAFY (LFY) transcription factor is a key regulator of floral meristem emergence and identity. LFY interacts genetically and physically with UNUSUAL FLORAL ORGANS, a substrate adaptor of CULLIN1-RING ubiquitin ligase complexes (CRL1). The functionally redundant genes BLADE ON PETIOLE1 (BOP1) and -2 (BOP2) are potential candidates to regulate LFY activity and have recently been shown to be substrate adaptors of CULLIN3 (CUL3)-RING ubiquitin ligases (CRL3). We tested the hypothesis that LFY activity is controlled by BOPs and CUL3s in plants and that LFY is a substrate for ubiquitination by BOP-containing CRL3 complexes. When constitutively expressed, LFY activity is fully dependent on BOP2 as well as on CUL3A and B to regulate target genes such as APETALA1 and to induce ectopic flower formation. We also show that LFY and BOP2 proteins interact physically and that LFY-dependent ubiquitinated species are produced in vitro in a reconstituted cell-free CRL3 system in the presence of LFY, BOP2 and CUL3. This new post-translational regulation of LFY activity by CRL3 complexes makes it a unique transcription factor subjected to a positive dual regulation by both CRL1 and CRL3 complexes and suggests a novel mechanism for promoting flower development.
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http://dx.doi.org/10.1111/nph.15329DOI Listing
October 2018

BLADE-ON-PETIOLE proteins act in an E3 ubiquitin ligase complex to regulate PHYTOCHROME INTERACTING FACTOR 4 abundance.

Elife 2017 08 22;6. Epub 2017 Aug 22.

Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.

Both light and temperature have dramatic effects on plant development. Phytochrome photoreceptors regulate plant responses to the environment in large part by controlling the abundance of PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors. However, the molecular determinants of this essential signaling mechanism still remain largely unknown. Here, we present evidence that the () genes, which have previously been shown to control leaf and flower development in Arabidopsis, are involved in controlling the abundance of PIF4. Genetic analysis shows that promotes photo-morphogenesis and modulates thermomorphogenesis by suppressing activity, through a reduction in PIF4 protein level. In red-light-grown seedlings PIF4 ubiquitination was reduced in the mutant. Moreover, we found that BOP proteins physically interact with both PIF4 and CULLIN3A and that a CULLIN3-BOP2 complex ubiquitinates PIF4 in vitro. This shows that BOP proteins act as substrate adaptors in a CUL3 E3 ubiquitin ligase complex, targeting PIF4 proteins for ubiquitination and subsequent degradation.
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http://dx.doi.org/10.7554/eLife.26759DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5582868PMC
August 2017

Class I KNOX transcription factors promote differentiation of cambial derivatives into xylem fibers in the Arabidopsis hypocotyl.

Development 2014 Nov;141(22):4311-9

Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden Department of Forest Botany and Tree Physiology, University of Göttingen, Göttingen DE-37077, Germany

The class I KNOX transcription factors SHOOT MERISTEMLESS (STM) and KNAT1 are important regulators of meristem maintenance in shoot apices, with a dual role of promoting cell proliferation and inhibiting differentiation. We examined whether they control stem cell maintenance in the cambium of Arabidopsis hypocotyls, a wood-forming lateral meristem, in a similar fashion as in the shoot apical meristem. Weak loss-of-function alleles of KNAT1 and STM led to reduced formation of xylem fibers - highly differentiated cambial derivatives - whereas cell proliferation in the cambium was only mildly affected. In a knat1;stm double mutant, xylem fiber differentiation was completely abolished, but residual cambial activity was maintained. Expression of early and late markers of xylary cell differentiation was globally reduced in the knat1;stm double mutant. KNAT1 and STM were found to act through transcriptional repression of the meristem boundary genes BLADE-ON-PETIOLE 1 (BOP1) and BOP2 on xylem fiber differentiation. Together, these data indicate that, in the cambium, KNAT1 and STM, contrary to their function in the shoot apical meristem, promote cell differentiation through repression of BOP genes.
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http://dx.doi.org/10.1242/dev.111369DOI Listing
November 2014

The BLADE ON PETIOLE genes act redundantly to control the growth and development of lateral organs.

Development 2005 May 30;132(9):2203-13. Epub 2005 Mar 30.

Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, S-90183 Umeå, Sweden.

Developmental processes in multicellular organisms involve an intricate balance between mechanisms that promote cell division activity and growth, and others that promote cell differentiation. Leaf development in Arabidopsis thaliana is controlled by genes like BLADE ON PETIOLE1 (BOP1), which prevent the development of ectopic meristematic activity that leads to the formation of new organs, and JAGGED (JAG), which control the proximodistal development of the leaf by regulating cell-division activity. We have isolated and characterized the BOP1 gene together with a functionally redundant close homolog that we name BOP2. The BOP genes are members of a gene family containing ankyrin repeats and a BTB/POZ domain, suggesting a role in protein-protein interaction. We show that the BOP genes are expressed in the proximal parts of plant lateral organs where they repress the transcription not only of class 1 knox genes but also of JAG. We also show that the BOP genes are acting together with the flower meristem identity gene LEAFY in the suppression of bract formation. These findings show that the BOP genes are important regulators of the growth and development of lateral organs.
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http://dx.doi.org/10.1242/dev.01815DOI Listing
May 2005