A mutation in the cytosolic O-acetylserine (thiol) lyase induces a genome-dependent early leaf death phenotype in Arabidopsis

Comprehensive Analysis of the OASTL Gene Family in Potato (Solanum tuberosum L.) and Its Expression Under Abiotic Stress

O-acetylserine (thiol) lyase is a pivotal enzyme in plant cysteine biosynthesis, which is crucial for promoting plant growth, development, and resisting abiotic stress. However, the related studies on the potato OASTL gene family (StOASTL) have not been reported. In the present study, we identified 11 members of the StOASTL gene family, conducting a thorough analysis encompassing chromosome distribution, protein physicochemical properties, gene structure, protein-conserved motifs, and gene replication events. Phylogenetic scrutiny delineated these 11 StOASTLs into five distinct subfamilies. Using RNA-seq from the Potato Genome Sequencing Consortium (PGSC), we investigated the expression profile of StOASTLs in different tissues of DM (double-monoploid) potato and under abiotic/biotic stress, hormone treatment, and biostimulant treatment. The results showed that one of the StOASTLs (Soltu09G024390) was differentially expressed under different abiotic stresses and hormone treatments. Our findings showcased the differential response of one StOASTL (Soltu09G024390) to a spectrum of abiotic stresses and hormone treatments. Soltu09G024390 was earmarked as a candidate gene and successfully cloned. Functional validation through yeast stress assays demonstrated that the heterologous expression of Soltu09G024390 bolstered yeast tolerance to salt and cadmium stresses. This study provides a theoretical basis for revealing the role of the StOASTL family in potato response to abiotic stress and valuable insights for further study of the biological functions of StOASTL.

In Vivo Proximity Cross-Linking and Immunoprecipitation of Cell Wall Epitopes Identify Proteins Associated with the Biosynthesis of Matrix Polysaccharides

Identification of proteins involved in cell wall matrix polysaccharide biosynthesis is crucial to understand plant cell wall biology. We utilized in vivo cross-linking and immunoprecipitation with cell wall antibodies that recognized xyloglucan, xylan, mannan, and homogalacturonan to capture proteins associated with matrix polysaccharides in Arabidopsis protoplasts. The use of cross-linkers allowed us to capture proteins actively associated with cell wall polymers, including those directly interacting with glycans via glycan-protein (GP) cross-linkers and those associated with proteins linked to glycans via a protein-protein (PP) cross-linker. Immunoprecipitations led to the identification of 65 Arabidopsis protein IDs localized in the Golgi, ER, plasma membrane, and others without subcellular localization data. Among these, we found several glycosyltransferases directly involved in polysaccharide synthesis, along with proteins related to cell wall modification and vesicle trafficking. Protein interaction networks from DeepAraPPI and AtMAD databases showed interactions between various IDs, including those related to cell-wall-associated proteins and membrane/vesicle trafficking proteins. Gene expression and coexpression analyses supported the presence and relevance of the proteins to the cell wall processes. Reverse genetic studies using T-DNA insertion mutants of selected proteins revealed changes in cell wall composition and saccharification, further supporting their potential roles in cell wall biosynthesis. Overall, our approach represents a novel approach for studying cell wall polysaccharide biosynthesis and associated proteins, providing advantages over traditional immunoprecipitation techniques. This study provides a list of putative proteins associated with different matrix polysaccharides for further investigation and highlights the complexity of cell wall biosynthesis and trafficking within plant cells.

Inhibition of O-acetylserine (thiol) lyase as a promising new mechanism of action for herbicides

Enzymes of the sulfur assimilation pathway of plants have been identified as potential targets for herbicide development, given their crucial role in synthesizing amino acids, coenzymes, and various sulfated compounds. In this pathway, O-acetylserine (thiol) lyase (OAS-TL; EC 2.5.1.47) catalyzes the synthesis of L-cysteine through the incorporation of sulfate into O-acetylserine (OAS). This study used an in silico approach to select seven inhibitors for OAS-TL. The in silico experiments revealed that S-benzyl-L-cysteine (SBC) had a better docking score (-7.0 kcal mol-1) than the substrate OAS (-6.6 kcal mol-1), indicating its suitable interaction with the active site of the enzyme. In vitro experiments showed that SBC is a non-competitive inhibitor of OAS-TL from Arabidopsis thaliana expressed heterologously in Escherichia coli, with a Kic of 4.29 mM and a Kiu of 5.12 mM. When added to the nutrient solution, SBC inhibited the growth of maize and morning glory weed plants due to the reduction of L-cysteine synthesis. Remarkably, morning glory was more sensitive than maize. As proof of its mechanism of action, L-cysteine supplementation to the nutrient solution mitigated the inhibitory effect of SBC on the growth of morning glory. Taken together, our data suggest that reduced L-cysteine synthesis is the primary cause of growth inhibition in maize and morning glory plants exposed to SBC. Furthermore, our findings indicate that inhibiting OAS-TL could potentially be a novel approach for herbicidal action.

Oak stands along an elevation gradient have different molecular strategies for regulating bud phenology

BACKGROUND

Global warming raises serious concerns about the persistence of species and populations locally adapted to their environment, simply because of the shift it produces in their adaptive landscape. For instance, the phenological cycle of tree species may be strongly affected by higher winter temperatures and late frost in spring. Given the variety of ecosystem services they provide, the question of forest tree adaptation has received increasing attention in the scientific community and catalyzed research efforts in ecology, evolutionary biology and functional genomics to study their adaptive capacity to respond to such perturbations.

RESULTS

In the present study, we used an elevation gradient in the Pyrenees Mountains to explore the gene expression network underlying dormancy regulation in natural populations of sessile oak stands sampled along an elevation cline and potentially adapted to different climatic conditions mainly driven by temperature. By performing analyses of gene expression in terminal buds we identified genes displaying significant dormancy, elevation or dormancy-by-elevation interaction effects. Our Results highlighted that low- and high-altitude populations have evolved different molecular strategies for minimizing late frost damage and maximizing the growth period, thereby increasing potentially their respective fitness in these contrasting environmental conditions. More particularly, population from high elevation overexpressed genes involved in the inhibition of cell elongation and delaying flowering time while genes involved in cell division and flowering, enabling buds to flush earlier were identified in population from low elevation.

CONCLUSION

Our study made it possible to identify key dormancy-by-elevation responsive genes revealing that the stands analyzed in this study have evolved distinct molecular strategies to adapt their bud phenology in response to temperature.

Ubiquitome profiling reveals a regulatory pattern of UPL3 with UBP12 on metabolic-leaf senescence

The HECT-type UPL3 ligase plays critical roles in plant development and stress protection, but understanding of its regulation remains limited. Here, the multi-omics analyses of ubiquitinated proteins in <i>upl3</i> mutants were performed. A landscape of UPL3-dependent ubiquitinated proteins is constructed: Preferential ubiquitination of proteins related to carbon fixation represented the largest set of proteins with increased ubiquitination in the <i>upl3</i> plant, including most of carbohydrate metabolic enzymes, BRM, and variant histone, whereas a small set of proteins with reduced ubiquitination caused by the <i>upl3</i> mutation were linked to cysteine/methionine synthesis, as well as hexokinase 1 (HXK1) and phosphoenolpyruvate carboxylase 2 (PPC2). Notably, ubiquitin hydrolase 12 (UBP12), BRM, HXK1, and PPC2 were identified as the UPL3-interacting partners in vivo and in vitro. Characterization of <i>brm</i>, <i>upl3</i>, <i>ppc2</i>, <i>gin2</i>, and <i>ubp12</i> mutant plants and proteomic and transcriptomic analysis suggested that UPL3 fine-tunes carbohydrate metabolism, mediating cellular senescence by interacting with UBP12, BRM, HXK1, and PPC2. Our results highlight a regulatory pattern of UPL3 with UBP12 as a hub of regulator on proteolysis-independent regulation and proteolysis-dependent degradation.

Unraveling hydrogen sulfide-promoted lateral root development and growth in mangrove plant Kandelia obovata: insight into regulatory mechanism by TMT-based quantitative proteomic approaches

Mangroves are the main intertidal ecosystems with varieties of root types along the tropical and subtropical coastlines around the world. The typical characteristics of mangrove habitats, including the abundant organic matter and nutrients, as well as the strong reductive environment, are favor for the production of hydrogen sulfide (H2S). H2S, as a pivotal signaling molecule, has been evidenced in a wide variety of plant physiological and developmental processes. However, whether H2S functions in the mangrove root system establishment is not clear yet. Here, we reported the possible role of H2S in regulation of Kandelia obovata root development and growth by tandem mass tag (TMT)-based quantitative proteomic approaches coupled with bioinformatic methods. The results showed that H2S could induce the root morphogenesis of K. obovata in a dose-dependent manner. The proteomic results successfully identified 8075 proteins, and 697 were determined as differentially expressed proteins. Based on the functional enrichment analysis, we demonstrated that H2S could promote the lateral root development and growth by predominantly regulating the proteins associated with carbohydrate metabolism, sulfur metabolism, glutathione metabolism and other antioxidant associated proteins. In addition, transcriptional regulation and brassinosteroid signal transduction associated proteins also act as important roles in lateral root development. The protein-protein interaction analysis further unravels a complicated regulation network of carbohydrate metabolism, cellular redox homeostasis, protein metabolism, secondary metabolism, and amino acid metabolism in H2S-promoted root development and growth of K. obovata. Overall, our results revealed that H2S could contribute to the morphogenesis of the unique root system of mangrove plant K. obovata, and play a positive role in the adaption of mangrove plants to intertidal habitats.

A molecular switch in sulfur metabolism to reduce arsenic and enrich selenium in rice grain

Rice grains typically contain high levels of toxic arsenic but low levels of the essential micronutrient selenium. Anthropogenic arsenic contamination of paddy soils exacerbates arsenic toxicity in rice crops resulting in substantial yield losses. Here, we report the identification of the gain-of-function arsenite tolerant 1 (astol1) mutant of rice that benefits from enhanced sulfur and selenium assimilation, arsenic tolerance, and decreased arsenic accumulation in grains. The astol1 mutation promotes the physical interaction of the chloroplast-localized O-acetylserine (thiol) lyase protein with its interaction partner serine-acetyltransferase in the cysteine synthase complex. Activation of the serine-acetyltransferase in this complex promotes the uptake of sulfate and selenium and enhances the production of cysteine, glutathione, and phytochelatins, resulting in increased tolerance and decreased translocation of arsenic to grains. Our findings uncover the pivotal sensing-function of the cysteine synthase complex in plastids for optimizing stress resilience and grain quality by regulating a fundamental macronutrient assimilation pathway.

Contamination of paddy soils can lead to toxic arsenic accumulation in rice grains and low levels of the micronutrient selenium. Here the authors show that a gain of function mutant affecting an O-acetylserine (thiol) lyase enhances sulfur and selenium assimilation while reducing arsenic accumulation in grains.

Appraisal of H2S metabolism in Arabidopsis thaliana: In silico analysis at the subcellular level

Hydrogen sulfide (H₂S) has become a new signal molecule in higher plants which seems to be involved in almost all physiological processes from seed germination, root and plant growth until flowering and fruit ripening. Moreover, H₂S also participates in the mechanism of response against adverse environmental stresses. However, its basic biochemistry in plant cells can be considered in a nascent stage. Using the available information of the model plant Arabidopsis thaliana, the goal of the present study is to provide a broad overview of H₂S metabolism and to display an in silico analysis of the 26 enzymatic components involved in the metabolism of H₂S and their subcellular compartmentation (cytosol, chloroplast and mitochondrion) thus providing a wide picture of the cross-talk inside the organelles and amongst them and, consequently, to get a better understanding of the cellular and tissue implications of H₂S. This information will be also relevant for other crop species, especially those whose whole genome is not yet available.

Dissecting MicroRNA-mRNA Regulatory Networks Underlying Sulfur Assimilation and Cadmium Accumulation in Poplar Leaves

The process of cadmium (Cd) accumulation and detoxification under different sulfur levels remains largely unknown in woody plants. To investigate the physiological and transcriptomic regulation mechanisms of poplars in response to different sulfate (S) supply levels and Cd exposure, we exposed Populus deltoides saplings to one of the low, moderate and high S levels together with either 0 or 50 µM Cd. Cd accumulation was decreased in low S-treated poplar leaves, and it tended to be increased in high S-supplied leaves under the Cd exposure condition. Sulfur nutrition was deficient in low S-supplied poplars, and it was improved in high S-treated leaves. Cd exposure resulted in lower sulfur level in the leaves supplied with moderate S, it exacerbated a Cd-induced sulfur decrease in low S-treated leaves and it caused a higher sulfur concentration in high S-supplied leaves. In line with the physiological changes, a number of mRNAs and microRNAs (miRNAs) involved in Cd accumulation and sulfur assimilation were identified and the miRNA-mRNA networks were dissected. In the networks, miR395 and miR399 members were identified as hub miRNAs and their targets were ATP sulfurylase 3 (ATPS3) and phosphate 2 (PHO2), respectively. These results suggest that Cd accumulation and sulfur assimilation are constrained by low and enhanced by high S supply, and Cd toxicity is aggravated by low and relieved by high S in poplar leaves, and that miRNA-mRNA regulatory networks play pivotal roles in sulfur-mediated Cd accumulation and detoxification in Cd-exposed poplars.

OASTL-A1 functions as a cytosolic cysteine synthase and affects arsenic tolerance in rice

Arsenic (As) contamination in paddy soil can cause phytotoxicity and elevated As accumulation in rice grains. Arsenic detoxification is closely linked to sulfur assimilation, but the genes involved have not been described in rice. In this study, we characterize the function of OASTL-A1, an O-acetylserine(thiol) lyase, in cysteine biosynthesis and detoxification of As in rice. Tissue expression analysis revealed that OsOASTL-A1 is mainly expressed in roots at the vegetative growth stage and in nodes at the reproductive stage. Furthermore, the expression of OsOASTL-A1 in roots was strongly induced by As exposure. Transgenic rice plants expressing pOsOASTL-A1::GUS (β-glucuronidase) indicated that OsOASTL-A1 was strongly expressed in the outer cortex and the vascular cylinder in the root mature zone. Subcellular localization using OsOASTL-A1:eGFP (enhanced green fluorescent protein) fusion protein showed that OsOASTL-A1 was localized to the cytosol. In vivo and in vitro enzyme activity assays showed that OsOASTL-A1 possessed the O-acetylserine(thiol) lyase activity. Knockout of OsOASTL-A1 led to significantly lower levels of cysteine, glutathione, and phytochelatins in roots and increased sensitivity to arsenate stress. Furthermore, the osoastl-a1 knockout mutants reduced As accumulation in the roots, but increased As accumulation in shoots. We conclude that OsOASTL-A1 is the cytosolic O-acetylserine(thiol) lyase that plays an important role in non-protein thiol biosynthesis in roots for As detoxification.

β-Cyanoalanine Synthases and Their Possible Role in Pierid Host Plant Adaptation

Cyanide is generated in larvae of the glucosinolate-specialist Pieris rapae (Lepidoptera:Pieridae) upon ingestion of plant material containing phenylalanine-derived glucosinolates as chemical defenses. As these glucosinolates were widespread within ancient Brassicales, the ability to detoxify cyanide may therefore have been essential for the host plant shift of Pierid species from Fabales to Brassicales species giving rise to the Pierinae subfamily. Previous research identified β-cyanoalanine and thiocyanate as products of cyanide detoxification in P. rapae larvae as well as three cDNAs encoding the β-cyanoalanine synthases PrBSAS1-PrBSAS3. Here, we analyzed a total of eight species of four lepidopteran families to test if their cyanide detoxification capacity correlates with their feeding specialization. We detected β-cyanoalanine synthase activity in gut protein extracts of all six species tested, which included Pierid species with glucosinolate-containing host plants, Pierids with other hosts, and other Lepidoptera with varying food specialization. Rhodanese activity was only scarcely detectable with the highest levels appearing in the two glucosinolate-feeding Pierids. We then amplified by polymerase chain reaction (PCR) 14 cDNAs encoding β-cyanoalanine synthases from seven species. Enzyme characterization and phylogenetic analysis indicated that lepidopterans are generally equipped with one PrBSAS2 homolog with high affinity for cyanide. A second β-cyanoalanine synthase which grouped with PrBSAS3 was restricted to Pierid species, while a third variant (i.e., homologs of PrBSAS1), was only present in members of the Pierinae subfamily. These results are in agreement with the hypothesis that the host shift to Brassicales was associated with the requirement for a specialized cyanide detoxification machinery.

Generation of chromosomal deletions in dicotyledonous plants employing a user-friendly genome editing toolkit

Genome editing facilitated by Cas9-based RNA-guided nucleases (RGNs) is becoming an increasingly important and popular technique for reverse genetics in both model and non-model species. So far, RGNs were mainly applied for the induction of point mutations, and one major challenge consists in the detection of genome-edited individuals from a mutagenized population. Also, point mutations are not appropriate for functional dissection of non-coding DNA. Here, the multiplexing capacity of a newly developed genome editing toolkit was exploited for the induction of inheritable chromosomal deletions at six different loci in Nicotiana benthamiana and Arabidopsis. In both species, the preferential formation of small deletions was observed, suggesting reduced efficiency with increasing deletion size. Importantly, small deletions (<100 bp) were detected at high frequencies in N. benthamiana T0 and Arabidopsis T2 populations. Thus, targeting of small deletions by paired nucleases represents a simple approach for the generation of mutant alleles segregating as size polymorphisms in subsequent generations. Phenotypically selected deletions of up to 120 kb occurred at low frequencies in Arabidopsis, suggesting larger population sizes for the discovery of valuable alleles from addressing gene clusters or non-coding DNA for deletion by programmable nucleases.

Arabidopsis thaliana DM2h (R8) within the Landsberg RPP1-like Resistance Locus Underlies Three Different Cases of EDS1-Conditioned Autoimmunity

Plants have a large panel of nucleotide-binding/leucine rich repeat (NLR) immune receptors which monitor host interference by diverse pathogen molecules (effectors) and trigger disease resistance pathways. NLR receptor systems are necessarily under tight control to mitigate the trade-off between induced defenses and growth. Hence, mis-regulated NLRs often cause autoimmunity associated with stunting and, in severe cases, necrosis. Nucleocytoplasmic ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) is indispensable for effector-triggered and autoimmune responses governed by a family of Toll-Interleukin1-Receptor-related NLR receptors (TNLs). EDS1 operates coincidently or immediately downstream of TNL activation to transcriptionally reprogram cells for defense. We show here that low levels of nuclear-enforced EDS1 are sufficient for pathogen resistance in Arabidopsis thaliana, without causing negative effects. Plants expressing higher nuclear EDS1 amounts have the genetic, phenotypic and transcriptional hallmarks of TNL autoimmunity. In a screen for genetic suppressors of nuclear EDS1 autoimmunity, we map multiple, independent mutations to one gene, DM2h, lying within the polymorphic DANGEROUS MIX2 cluster of TNL RPP1-like genes from A. thaliana accession Landsberg erecta (Ler). The DM2 locus is a known hotspot for deleterious epistatic interactions leading to immune-related incompatibilities between A. thaliana natural accessions. We find that DM2h^Ler underlies two further genetic incompatibilities involving the RPP1-like^Ler locus and EDS1. We conclude that the DM2h^Ler TNL protein and nuclear EDS1 cooperate, directly or indirectly, to drive cells into an immune response at the expense of growth. A further conclusion is that regulating the available EDS1 nuclear pool is fundamental for maintaining homeostatic control of TNL immune pathways.

Plants tune their cellular and developmental programs to different environmental stimuli. Central players in the plant biotic stress response network are intracellular NLR receptors which intercept specific disease-inducing molecules (effectors) produced by pathogenic microbes. Variation in NLR gene repertoires between plant genetic lines is driven by pathogen selection pressure. One evolutionary question is how new, functional NLRs are assembled within a plant genome without mis-activating defense pathways, which can have strong negative effects on growth and fitness. This study focuses on a large, polymorphic sub-class of NLR receptors called TNLs present in dicotyledenous plant lineages. TNL receptors confer immunity to a broad range of pathogens. They also frequently underlie autoimmunity caused by their mis-regulation or deleterious allelic interactions with other genes in crosses between different genetic lines (hybrid incompatibility, HI). TNL pathogen-triggered and autoimmune responses require the conserved nucleocytoplasmic protein EDS1 to transcriptionally reprogram cells for defense. We discover in Arabidopsis thaliana that high levels of nuclear-enriched EDS1 induce transcriptional activation of defenses and growth inhibition without a pathogen effector stimulus. In a mutational screen, we identify one rapidly evolving TNL gene, DM2h^Ler, as a driver of nuclear EDS1 autoimmunity. DM2h^Ler also contributes to two separate cases of EDS1-dependent autoimmunity. Genetic cooperation between DM2h^Ler and EDS1 suggests a functional relationship in the transcriptional feed-forward regulation of defense pathways.

A spinach O-acetylserine(thiol)lyase homologue, SoCSaseLP, suppresses cysteine biosynthesis catalysed by other enzyme isoforms

An enzyme, O-acetylserine(thiol)lyase (OASTL), also known as O-acetylserine sulfhydrylase or cysteine synthase (CSase), catalyses the incorporation of sulfide into O-acetylserine and produces cysteine. We previously identified a cDNA encoding an OASTL-like protein from Spinacia oleracea, (SoCSaseLP), but a recombinant SoCSaseLP produced in Escherichia coli did not show OASTL activity. The exon-intron structure of the SoCSaseLP gene shared conserved structures with other spinach OASTL genes. The SoCSaseLP and a Beta vulgaris homologue protein, KMT13462, comprise a unique clade in the phylogenetic tree of the OASTL family. Interestingly, when the SoCSaseLP gene was expressed in tobacco plants, total OASTL activity in tobacco leaves was reduced. This reduction in total OASTL activity was most likely caused by interference by SoCSaseLP with cytosolic OASTL. To investigate the possible interaction of SoCSaseLP with a spinach cytosolic OASTL isoform SoCSaseA, a pull-down assay was carried out. The recombinant glutathione S-transferase (GST)-SoCSaseLP fusion protein was expressed in E. coli together with the histidine-tagged SoCSaseA protein, and the protein extract was subjected to glutathione affinity chromatography. The histidine-tagged SoCSaseA was co-purified with the GST-SoCSaseLP fusion protein, indicating the binding of SoCSaseLP to SoCSaseA. Consistent with this interaction, the OASTL activity of the co-purified SoCSaseA was reduced compared with the activity of SoCSaseA that was purified on its own. These results strongly suggest that SoCSaseLP negatively regulates the activity of other cytosolic OASTL family members by direct interaction.

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An enzyme, O-acetylserine(thiol)lyase (OASTL), catalyses cysteine synthesis.

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A member of spinach OASTL family, SoCSaseLP, did not show any OASTL activity.

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Ectopic expression of the SoCSaseLP gene caused a reduction of total OASTL activity.

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The SoCSaseLP inhibited cysteine synthesis by a spinach cytosolic OASTL protein.

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Negative regulation of cysteine synthesis by SoCSaseLP was proposed.

iTRAQ protein profile analysis of Citrus sinensis roots in response to long-term boron-deficiency

Seedlings of Citrus sinensis were fertilized with boron (B)-deficient (0μM H3BO3) or -sufficient (10μM H3BO3) nutrient solution for 15weeks. Thereafter, iTRAQ analysis was employed to compare the abundances of proteins from B-deficient and -sufficient roots. In B-deficient roots, 164 up-regulated and 225 down-regulated proteins were identified. These proteins were grouped into the following functional categories: protein metabolism, nucleic acid metabolism, stress responses, carbohydrate and energy metabolism, cell transport, cell wall and cytoskeleton metabolism, biological regulation and signal transduction, and lipid metabolism. The adaptive responses of roots to B-deficiency might include following several aspects: (a) decreasing root respiration; (b) improving the total ability to scavenge reactive oxygen species (ROS); and (c) enhancing cell transport. The differentially expressed proteins identified by iTRAQ are much larger than those detected using 2D gel electrophoresis, and many novel B-deficiency-responsive proteins involved in cell transport, biological regulation and signal transduction, stress responses and other metabolic processes were identified in this work. Our results indicate remarkable metabolic flexibility of citrus roots, which may contribute to the survival of B-deficient plants. This represents the most comprehensive analysis of protein profiles in response to B-deficiency.

BIOLOGICAL SIGNIFICANCE

In this study, we identified many new proteins involved in cell transport, biological regulation and signal transduction, stress responses and other metabolic processes that were not previously known to be associated with root B-deficiency responses. Therefore, our manuscript represents the most comprehensive analysis of protein profiles in response to B-deficiency and provides new information about the plant response to B-deficiency. This article is part of a Special Issue entitled: Translational Plant Proteomics.

Activation of R-mediated innate immunity and disease susceptibility is affected by mutations in a cytosolic O-acetylserine (thiol) lyase in Arabidopsis

O-acetylserine (thiol) lyases (OASTLs) are evolutionarily conserved proteins among many prokaryotes and eukaryotes that perform sulfur acquisition and synthesis of cysteine. A mutation in the cytosolic OASTL-A1 protein ONSET OF LEAF DEATH3 (OLD3) was previously shown to reduce the OASTL activity of the old3-1 protein in vitro and cause auto-necrosis in specific Arabidopsis accessions. Here we investigated why a mutation in this protein causes auto-necrosis in some but not other accessions. The auto-necrosis was found to depend on Recognition of Peronospora Parasitica 1 (RPP1)-like disease resistance R gene(s) from an evolutionarily divergent R gene cluster that is present in Ler-0 but not the reference accession Col-0. RPP1-like gene(s) show a negative epistatic interaction with the old3-1 mutation that is not linked to reduced cysteine biosynthesis. Metabolic profiling and transcriptional analysis further indicate that an effector triggered-like immune response and metabolic disorder are associated with auto-necrosis in old3-1 mutants, probably activated by an RPP1-like gene. However, the old3-1 protein in itself results in largely neutral changes in primary plant metabolism, stress defence and immune responses. Finally, we showed that lack of a functional OASTL-A1 results in enhanced disease susceptibility against infection with virulent and non-virulent Pseudomonas syringae pv. tomato DC3000 strains. These results reveal an interaction between the cytosolic OASTL and components of plant immunity.

Regulation of leaf senescence and crop genetic improvement

Leaf senescence can impact crop production by either changing photosynthesis duration, or by modifying the nutrient remobilization efficiency and harvest index. The doubling of the grain yield in major cereals in the last 50 years was primarily achieved through the extension of photosynthesis duration and the increase in crop biomass partitioning, two things that are intrinsically coupled with leaf senescence. In this review, we consider the functionality of a leaf as a function of leaf age, and divide a leaf's life into three phases: the functionality increasing phase at the early growth stage, the full functionality phase, and the senescence and functionality decreasing phase. A genetic framework is proposed to describe gene actions at various checkpoints to regulate leaf development and senescence. Four categories of genes contribute to crop production: those which regulate (I) the speed and transition of early leaf growth, (II) photosynthesis rate, (III) the onset and (IV) the progression of leaf senescence. Current advances in isolating and characterizing senescence regulatory genes are discussed in the leaf aging and crop production context. We argue that the breeding of crops with leaf senescence ideotypes should be an essential part of further crop genetic improvement.

Regulatory subunit B'gamma of protein phosphatase 2A prevents unnecessary defense reactions under low light in Arabidopsis

Light is an important environmental factor that modulates acclimation strategies and defense responses in plants. We explored the functional role of the regulatory subunit B'γ (B'γ) of protein phosphatase 2A (PP2A) in light-dependent stress responses of Arabidopsis (Arabidopsis thaliana). The predominant form of PP2A consists of catalytic subunit C, scaffold subunit A, and highly variable regulatory subunit B, which determines the substrate specificity of PP2A holoenzymes. Mutant leaves of knockdown pp2a-b'γ plants show disintegration of chloroplasts and premature yellowing conditionally under moderate light intensity. The cell-death phenotype is accompanied by the accumulation of hydrogen peroxide through a pathway that requires CONSTITUTIVE EXPRESSION OF PR GENES5 (CPR5). Moreover, the pp2a-b'γ cpr5 double mutant additionally displays growth suppression and malformed trichomes. Similar to cpr5, the pp2a-b'γ mutant shows constitutive activation of both salicylic acid- and jasmonic acid-dependent defense pathways. In contrast to cpr5, however, pp2a-b'γ leaves do not contain increased levels of salicylic acid or jasmonic acid. Rather, the constitutive defense response associates with hypomethylation of DNA and increased levels of methionine-salvage pathway components in pp2a-b'γ leaves. We suggest that the specific B'γ subunit of PP2A is functionally connected to CPR5 and operates in the basal repression of defense responses under low irradiance.