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Results for “Plant Biology”

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bioRxiv2019

Enhanced Disease Susceptibility 5 (EDS5) is required for N-hydroxy pipecolic acid formation

Pipecolic acid is essential for the establishment of systemic acquired resistance in plants. It is synthesized in the plastid and further processed in the cytosol to its active form N-hydroxy pipecolic acid. Here we provide strong evidence that the exporter Enhanced Disease Susceptibility 5 is required for the biosynthesis of not only salicylic acid, but also N-hydroxy pipecolic acid, suggesting that it represents a convergent point of plant immunity.

plant biology↗

bioRxiv2019

Auxin-Induced Actin Cytoskeleton Rearrangements Require AUX1

The actin cytoskeleton is required for cell expansion and is implicated in cellular responses to the plant growth hormone auxin. However, the molecular and cellular mechanisms that coordinate auxin signaling, cytoskeletal remodeling, and cell expansion are poorly understood. Previous studies have examined actin cytoskeleton responses to long-term auxin treatment, but plants respond to auxin over short timeframes, and growth changes within minutes of exposure to the hormone. To correlate actin arrays with degree of cell expansion, we used quantitative imaging tools to establish a baseline of actin organization, as well as of individual filament behaviors in root epidermal cells under control conditions and after treatment with a known inhibitor of root growth, the auxin indole-3-acetic acid (IAA). We found that cell length was highly predictive of actin array in control roots, and that short-term IAA treatment stimulated denser, more longitudinal, and more parallel arrays by inducing filament unbundling within minutes. By demonstrating that actin filaments were more \"organized\" after a treatment that stopped elongation, we show there is no direct relationship between actin organization and cell expansion and refute the hypothesis that \"more organized\" actin universally correlates with more rapidly growing root cells. The plasma membrane-bound auxin transporter AUXIN RESISTANT 1 (AUX1) has previously been shown necessary for archetypal short-term root growth inhibition in the presence of IAA. Although AUX1 was not previously suspected of being upstream of cytoskeletal responses to IAA, we used aux1 mutants to demonstrate that AUX1 is necessary for the full complement of actin rearrangements in response to auxin, and that cytoplasmic auxin in the form of NAA is sufficient to stimulate a partial actin response. Together, these results are the first to quantitate actin cytoskeleton response to short-term auxin treatments and demonstrate that AUX1 is necessary for short-term actin remodeling.\n\nOne sentence summaryThe Arabidopsis AUX1 auxin transport protein is necessary for actin cytoskeleton reorganization in response to phytohormone treatment.

plant biology↗

bioRxiv2019

Discovery of interaction-related sRNAs and their targets in the Brachypodium distachyon and Magnaporthe oryzae pathosystem

Microbial pathogens secrete small RNA (sRNA) effectors into plant hosts to aid infection by silencing transcripts of immunity and signaling-related genes through RNA interference (RNAi). Similarly, sRNAs from plant hosts have been shown to contribute to plant defense against microbial pathogens by targeting transcripts involved in virulence. This phenomenon is called bidirectional RNA communication or cross kingdom RNAi (ckRNAi). How far this RNAi-mediated mechanism is evolutionarily conserved is the subject of controversial discussions. We examined the bidirectional accumulation of sRNAs in the interaction of the hemibiotrophic rice blast fungus Magnaporthe oryzae (Mo) with the grass model plant Brachypodium distachyon (Bd). By comparative deep sequencing of sRNAs and mRNAs from axenic fungal cultures and infected leaves and roots, we found a wide range of fungal sRNAs that accumulated exclusively in infected tissues. Amongst those, 20-21 nt candidate sRNA effectors were predicted in silico by selecting those Mo reads that had complementary mRNA targets in Bd. Many of those mRNAs predicted to be targeted by Mo sRNAs were differentially expressed, particularly in the necrotrophic infection phase, including gene transcripts involved in plant defense responses and signaling. Vice versa, by applying the same strategy to identify Bd sRNA effectors, we found that Bd produced sRNAs targeting a variety of fungal transcripts, encoding fungal cell wall components, virulence genes and transcription factors. Consistent with function as effectors of these Bd sRNAs, their predicted fungal targets were significantly down-regulated in the infected tissues compared to axenic cultures, and deletion mutants for some of these target genes showed heavily impaired virulence phenotypes. Overall, this study provides the first experimentally-based evidence for bidirectional ckRNAi in a grass-fungal pathosystem, paving the way for further validation of identified sRNA-target duplexes and contributing to the emerging research on naturally occurring cross-kingdom communication and its implications for agriculture on staple crops.\n\nAuthor SummaryIn the present work, we provide first experimental evidence for bidirectional RNA communication in a grass-fungal pathosystem. We deployed the monocotyledonous plant Brachypodium distachyon, which is a genetic model for the staple crops wheat and rice, to investigate the interaction-related sRNAs for their role in RNA communication. By applying a previously published bioinformatics pipeline for the detection of sRNA effectors we identified potential plant targets for fungal sRNAs and vice versa, fungal targets for plant sRNAs. Inspection of the respective targets confirmed their downregulation in infected relative to uninfected tissues and fungal axenic cultures, respectively. By focusing on potential fungal targets, we identified several genes encoding fungal cell wall components, virulence proteins and transcription factors. The deletion of those fungal targets has already been shown to produce disordered virulence phenotypes. Our findings establish the basis for further validation of identified sRNA-mRNA target duplexes and contribute to the emerging research on naturally occurring cross-kingdom communication and its implications for agriculture.

plant biology↗

bioRxiv2019

Chloroplast nucleoids are highly dynamic in ploidy, number, and structure during angiosperm leaf development

Chloroplast nucleoids are large, compact nucleoprotein structures containing multiple copies of the plastid genome. Studies on structural and quantitative changes of plastid DNA (ptDNA) during leaf development are scarce and have produced controversial data. We have systematically investigated nucleoid dynamics and ptDNA quantities in mesophyll of Arabidopsis, tobacco, sugar beet, and maize from the early post-meristematic stage until necrosis. DNA of individual nucleoids was quantified by DAPI-based supersensitive epifluorescence microscopy. Nucleoids occurred in scattered, stacked or ring-shaped arrangements and in recurring patterns during leaf development remarkably similar between the species studied. Nucleoids per organelle varied from few in meristematic plastids to >30 in mature chloroplasts (corresponding to about 20-750 nucleoids per cell). Nucleoid ploidies ranged from haploid to >20-fold even within individual organelles, with average values between 2.6- and 6.7-fold and little changes during leaf development. DNA quantities per organelle increased gradually from about a dozen plastome copies in tiny plastids of apex cells to 70-130 copies in chloroplasts of about 7 m diameter in mature mesophyll tissue, and from about 80 plastome copies in meristematic cells to 2,600-3,300 copies in mature diploid mesophyll cells without conspicuous decline during leaf development. Pulsed-field electrophoresis, restriction of high-molecular weight DNA from chloroplasts and gerontoplasts, and CsCl equilibrium centrifugation of single- and double-stranded ptDNA revealed no noticeable fragmentation of the organelle DNA during leaf development, implying that plastid genomes in mesophyll tissues are remarkably stable until senescence. Significance StatementPlastid DNA is organized in nucleoids that are highly dynamic in organization, structure and amount during leaf development. The present investigation fully resolves now this dynamic and is a precise cytogenetic characterization of nucleoids DNA spanning the entire life cycle of the leaf.

plant biology↗

bioRxiv2019

Analysis of soybean germination, emergence, and prediction of a possible northward expansion of the crop under climate change

Soybean (Glycine max (L.) Merr.) has potential to improve sustainability of agricultural production systems. A higher focus on this crop is needed to re-launch its production in the EU. A better understanding of key determinants affecting soybean establishment represents a first step to facilitate its adoption in cropping systems. To this objective, we conducted laboratory and field experiments in order to better characterize seed germination and seedling growth in relation to temperatures, water content, and soil structure. We then used these data to parametrize the SIMPLE crop emergence model and to evaluate its prediction quality, by comparing observed field germination and emergence data with the predicted ones. Finally, we performed a simulation study over the 2020-2100 period, for three sowing dates, from mid-March to mid-April, in the northern climate of France to evaluate whether future climate change will help expand soybean from Southern to Northern part of the country. Soybean germination was very fast, taking only 15 {degrees}C days to reach 50% germination at optimal conditions. The base, optimum and maximum temperatures were determined as 4, 30 and 40{degrees}C, respectively while the base water potential was -0.7 MPa, indicating a high sensitivity to water stress. The SIMPLE model well-predicted germination and emergence courses and their final rates, compared with the observed field data. The simulation study showed average emergence rate ranging from 61 to 78% with little variability among sowing dates and periods, but a high variability between years. Main causes of non-emergence were seedling mortality due to clods or soil surface crust followed by non-germination and seedling mortality due to drought, especially for mid-April sowing. These results provide a better knowledge of soybean establishment that are encouraging to introduce soybean with early sowings to diversify current cropping systems.

plant biology↗

bioRxiv2019

Role of Triose Phosphate Utilization in photosynthetic response of rice to variable carbon dioxide levels and plant source-sink relations

This study aimed to understand the physiological bases of rice photosynthesis response to C source-sink imbalances, with focus on dynamics of the photosynthetic parameter TPU (Triose Phosphate Utilization). A dedicated experiment was replicated twice on IR64 indica rice cultivar in controlled environments. Plants were grown under the current ambient CO2 concentration until heading, thereafter, two CO2 treatments (400 and 800 mol mol-1) were compared in the presence and absence of a panicle pruning treatment modifying the C sink. At two weeks after heading, photosynthetic parameters derived from CO2 response curves, and nonstructural carbohydrate content of flag leaf and internodes were measured 3-4 times of day. Spikelet number per panicle and flag leaf area on the main culm were recorded. Net C assimilation and TPU decreased progressively after midday in panicle-pruned plants, especially under 800 mol mol-1. This TPU reduction was explained by sucrose accumulation in the flag leaf resulting from the sink limitation. It is suggested that TPU is involved in rice photosynthesis regulation under elevated CO2 conditions, and that sink limitation effects should be considered in crop models.\n\nHighlightThis study provide new insights in the effect of C source-sink relationships on rice photosynthesis. TPU should be considered in photosynthesis studies under severe source-sink imbalance at elevated CO2.

plant biology↗

bioRxiv2019

Genome-Wide Association Study of Resistance to Bean Fly and Population Structure of Market Classes of Common Bean

Common bean (Phaesolus vulgaris L.) distribution across eastern, central and southern Africa region is widely driven by choice of grain types, which is affecting the genetic composition and adaptation to target production environments for biotic and abiotic constraints. Two bean fly species, Ophiomyia spencerella and Ophiomyia phaseoli are harmful insect pests of beans causing significant yield losses. Our objectives were to assess the population structure of common bean germplasm of different market classes and to identify polymorphic loci associated with resistance to O. spencerella. The study was carried out on a diversity panel of 284 genotypes using 9040 SNP markers. The genotypes were differentiated in to 14 distinct clusters. The mean FST of 0.4849, revealed major differentiation among the populations. Andean gene pool was more diverse compared to Mesoamerica gene pool which could be attributed to preference for large seeded cultivars. Multi-dimensional scaling and structure analyses revealed admixture among seed types. From genome wide association studies (GWAS), major genomic regions associated with O. spencerella resistance were identified on chromosome 1 (Pv01). The most significant SNP on Pv01 was aligned to gene PHAVU_001G075500g that is related to the Interleukin-1 receptor-associated kinase (IRAK) pathway, critical in regulating inherent immune responses to disease infection and insect herbivore attack. The diversity uncovered on the basis of market classes of beans and the presence of QTL regions associated with resistance to bean fly could serve as a valuable genetic resource for improvement of beans of different seed types in eastern and southern Africa region.\n\nCore IdeasO_LIGWAS revealed major loci associated with bean fly resistance on chromosome 01.\nC_LIO_LINew sources of resistance to bean fly were uncovered from different market classes.\nC_LIO_LIGenetic diversity uncovered is based on recent farmer preferences selection events.\nC_LI

plant biology↗

bioRxiv2019

Rapid identification of homozygosity and site of wild relative introgressions in wheat through chromosome-specific KASP genotyping assays

For future food security it is important that wheat, one of the most widely consumed crops in the world, can survive the threat of abiotic and biotic stresses. New genetic variation is currently being introduced into wheat through introgressions from its wild relatives. For trait discovery, it is necessary that each introgression is homozygous and hence stable. Breeding programs rely on efficient genotyping platforms for marker-assisted selection (MAS). Recently, single nucleotide polymorphism (SNP) based markers have been made available on high-throughput Axiom(R) SNP genotyping arrays. However, these arrays are inflexible in their design and sample numbers, making their use unsuitable for long-term MAS. SNPs can potentially be converted into Kompetitive allele-specific PCR (KASP) assays which are comparatively cost-effective and efficient for low-density genotyping of introgression lines. However, due to the polyploid nature of wheat, KASP assays for homoeologous SNPs can have difficulty in distinguishing between heterozygous and homozygous hybrid lines in a backcross population. To identify co-dominant SNPs, that can differentiate between heterozygotes and homozygotes, we PCR-amplified and sequenced genomic DNA from potential single-copy regions of the wheat genome and compared them to orthologous copies from different wild relatives. A panel of 620 chromosome-specific KASP assays have been developed that allow rapid detection of wild relative segments and provide information on their homozygosity and site of introgression in the wheat genome. A set of 90 chromosome-nonspecific assays was also produced that can be used for genotyping introgression lines. These multipurpose KASP assays represent a powerful tool for wheat breeders worldwide.

plant biology↗

bioRxiv2019

Why high yield QTLs did not succeed in preventing yield stagnation in rice?

Rice plays a vital role in global food security, and its yield needs to be increased to meet escalating demand. Although many high yield quantitative trait loci (QTLs) have been identified in the last decades, rice grain yield in the main rice-producing countries is stagnating since the middle of the 1990s. By summarizing the yield performance of high-yielding QTL lines, we found that almost all the high-yielding QTL introduced lines had no practical usage in current high yield breeding programs, due mainly to their low absolute grain yield. Further analysis showed that scientists primarily focused on spikelets number per panicle alone rather than other yield traits, and, in most of the studies, the yield increase was referenced to very old cultivars. By analyzing the yield traits correlations across cultivars in both field and pot conditions, and yield traits correlations across different eco-sites using the same cultivars, we demonstrated that the rice high yield will be rarely achieved by using single-trait approaches due to the traits trade-offs. Building on this, several recommendations are provided to the next generation of biotechnological breeding in rice.

plant biology↗

bioRxiv2019

BIOTIN ATTACHMENT DOMAIN-CONTAINING proteins, inhibitors of ACCase, are regulated by WRINKLED1

WRINKLED1 (WRI1) is a transcriptional activator that binds to AW boxes in the promoters of many genes from central metabolism and FA synthesis, resulting in their transcription. BIOTIN ATTACHMENT DOMAIN-CONTAINING (BADC) proteins are homologs of BIOTIN CARBOXYL CARRIER PROTEIN (BCCP) that lack a biotin-attachment domain and are therefore inactive. In the presence of excess FA, BADC1 and BADC3 are primarily responsible for the observed long-term irreversible inhibition of ACETYL-COA CARBOXYLASE (ACCase), and consequently FA synthesis. Purified WRI1 bound with high affinity (Kds in the low nanomolar range) to canonical AW-boxes from the promoters of all three BADC genes. Consistent with this observation, the expression of BADC1, BADC2 and BADC3 genes and BADC1 protein levels were reduced in wri1-1 relative to wild type (WT), and BADCs gene expression and BADC1 protein levels also were elevated upon WRI1 overexpression. The double mutant badc1badc2 phenocopied wri1-1 with respect to both reduction in root length, and elevation of indole-3-acetic acid-Asp (IAA-Asp) levels relative to WT. Overexpression of BADC1 in wri1-1 decreased its IAA-Asp and partially rescued its short-root phenotype demonstrating a role for BADCs in seedling establishment. That WRI1 positively regulates genes encoding both FA synthesis and BADCs i.e., conditional inhibitors of FA synthesis, represents a coordinated mechanism to achieve lipid homeostasis in which plants couple the transcription their FA synthetic capacity with their capacity to biochemically downregulate it.\n\nOne sentence summaryWRI1 regulates genes encoding both fatty acid synthesis and inhibitors of FA synthesis (BADCs), creating a lipid homeostatic mechanism in which the transcription of FA synthetic capacity is coordinated with the capacity to biochemically downregulate FA synthesis.

plant biology↗

bioRxiv2019

An asexual flower of Silene latifolia and Microbotryum lychnidis-dioicae promoting its sexual-organ development

Silene latifolia is a dioecious flowering plant with sex chromosomes in the family Caryophyllaceae. Development of a gynoecium and stamens are suppressed in the male and female flowers of S. latifolia, respectively. Microbtryum lychnidis-dioicae promotes stamen development when it infects the female flower. If suppression of the stamen and gynoecium development is regulated by the same mechanism, suppression of gynoecium and stamen development is released simultaneously with the infection by M. lychnidis-dioicae. To assess this hypothesis, an asexual mutant, without gynoecium or stamen, was infected with M. lychnidis-dioicae. A filament of the stamen in the infected asexual mutant was elongated at stages 11 and 12 of the flower bud development as well as the male, but the gynoecium did not form. Instead of the gynoecium, a filamentous structure was suppressed as in the male flower. Developmental suppression of the stamen was released by M. lychnidis-dioicae, but that of gynoecium development was not released. It is thought, therefore, that the suppression of gynoecium development was not released by the infection of M. lychnidis-dioicae. M. lychnidis-dioicae would have a function similar to SPF since the elongation of the stamen that is not observed in the healthy asexual mutant was observed after stage 8 of flower bud development. Such an infection experiment also that the Y chromosome of the asexual mutant has genes related to the differentiation of archesporial cells, but none related to maturation of the tapetal cells.

plant biology↗

bioRxiv2019

Application of TurboID-mediated proximity labeling for mapping a GSK3 kinase signaling network in Arabidopsis

Transient protein-protein interactions (PPIs), such as those between posttranslational modifying enzymes and their substrates, play key roles in cellular regulation, but are difficult to identify. Here we demonstrate the application of enzyme-catalyzed proximity labeling (PL), using the engineered promiscuous biotin ligase TurboID, as a sensitive method for characterizing PPIs in signaling networks. We show that TurboID fused with the GSK3-like kinase BIN2 or a PP2A phosphatase biotinylates their known substrate, the BZR1 transcription factor, with high specificity and efficiency. We optimized the protocol of biotin labeling and affinity purification in transgenic Arabidopsis expressing a BIN2-TurboID fusion protein. Subsequent quantitative mass spectrometry (MS) analysis identified about three hundred proteins biotinylated by BIN2-TurboID more efficiently than the YFP-TurboID control. These include a significant subset of previously proven BIN2 interactors and a large number of new BIN2-proximal proteins that uncover a broad BIN2 signaling network. Our study illustrates that PL-MS using TurboID is a powerful tool for mapping signaling networks, and reveals broad roles of BIN2 kinase in cellular signaling and regulation in plants.\n\nImpact StatementTurboID-mediated proximity labeling is a powerful tool for protein interactomics in plants.

plant biology↗

bioRxiv2019

A light-dependent molecular link between competition cues and defense responses in plants

One of the principal internal signals controlling plant growth and defense is jasmonate (JA), a potent growth inhibitor that is simultaneously a central regulator of plant immunity to herbivores and pathogens. When shade-intolerant plants perceive the proximity of competitors using the photoreceptor phytochrome B (phyB), they accelerate growth and down-regulate JA responses. However, the mechanisms by which photoreceptors relay light cues to the JA signaling pathway are not understood. Here we identify a sulfotransferase (ST2a) that is strongly up-regulated by plant proximity perceived by phyB via the phyB-Phytochrome Interacting Factor (PIF) signaling module. By catalyzing the formation of a sulfated JA derivative, ST2a acts to degrade bioactive forms of JA and represents a direct molecular link between photoreceptors and hormone signaling in plants. The enzyme provides a molecular mechanism for prioritizing shade avoidance over defense under close plant competition.

plant biology↗

bioRxiv2019

Computational simulation of the reactive oxygen species and redox network in the regulation of chloroplast metabolism

Cells contain a thiol redox regulatory network to coordinate metabolic and developmental activities with exogenous and endogenous cues. This network controls the redox state and activity of many target proteins. Electrons are fed into the network from metabolism and reach the target proteins via redox transmitters such as thioredoxin (TRX) and NADPH-dependent thioredoxin reductases (NTR). Electrons are drained from the network by reactive oxygen species (ROS) through thiol peroxidases, e.g., peroxiredoxins (PRX). Mathematical modeling promises access to quantitative understanding of the network function and was implemented for the photosynthesizing chloroplast by using published kinetic parameters combined with fitting to known biochemical data. Two networks were assembled, namely the ferredoxin (FDX), FDX-dependent TRX reductase (FTR), TRX, fructose-1,6-bisphosphatase pathway with 2-cysteine PRX/ROS as oxidant, and separately the FDX, FDX-dependent NADP reductase (FNR), NADPH, NTRC-pathway for 2-CysPRX reduction. Combining both modules allowed drawing several important conclusions of network performance. The resting H2O2 concentration was estimated to be about 30 nM in the chloroplast stroma. The electron flow to metabolism exceeds that into thiol regulation of FBPase more than 7000-fold under physiological conditions. The electron flow from NTRC to 2-CysPRX is about 5.46-times more efficient than that from TRX-f1 to 2-CysPRX. Under severe stress (30 M H2O2) the ratio of electron flow to the thiol network relative to metabolism sinks to 1:251 whereas the ratio of electron flow from NTRC to 2-CysPRX and TRX-f1 to 2-CysPRX rises up to 1:80. Thus, the simulation provides clues on experimentally inaccessible parameters and describes the functional state of the chloroplast thiol regulatory network.\n\nAuthors summaryThe state of the thiol redox regulatory network is a fundamental feature of all cells and determines metabolic and developmental processes. However, only some parameters are quantifiable in experiments. This paper establishes partial mathematical models which enable simulation of electron flows through the regulatory system. This in turn allows for estimating rates and states of components of the network and to tentatively address previously unknown parameters such as the resting hydrogen peroxide levels or the expenditure of reductive power for regulation relative to metabolism. The establishment of such models for simulating the performance and dynamics of the redox regulatory network is of significance not only for photosynthesis but also, e.g., in bacterial and animal cells exposed to environmental stress or pathological disorders.

plant biology↗

bioRxiv2019

A cereal aphid effector promotes barley susceptibility in a species-specific manner through suppression of defence gene expression.

Aphids secrete diverse repertoires of effectors into their hosts to promote the infestation process. While \"omics\"-approaches facilitated the identification and comparison of effector repertoires from a number of aphid species, the functional characterization of these proteins has been limited to dicot (model) plants. The bird cherry-oat aphid Rhopalosiphum padi is a pest of cereal crops, including barley. Here, we extended efforts to characterize aphid effectors with regards to their role in promoting susceptibility to the R. padi-barley interaction. We selected 3 R. padi effectors based on sequences similarity to previously characterized M. persicae effectors and assessed their subcellular localisation, expression, and role in promoting plant susceptibility. Expression of R. padi effectors RpC002 and Rp1 in transgenic barley lines enhanced plant susceptibility to R. padi but not M. persicae, for which barley is a poor host. Characterization of Rp1 transgenic barley lines revealed reduced gene expression of plant hormone signalling genes relevant to plant-aphid interactions, indicating this effector enhances susceptibility by suppressing plant defences in barley. Our data suggests that some aphid effectors specifically function when expressed in host species, and feature activities that benefit their corresponding aphid species.

plant biology↗

bioRxiv2019

Overexpression of Medicago sativa glutamate-semialdehyde aminotransferase (GSA) gene in tobacco increased photosynthesis efficiency

To investigate the effect of increased glutamate-semialdehyde aminotransferase (GSA) on photosynthetic capacity and growth, tobacco (Nicoliana tabacum L. Xanti) plants with increased levels of glutamate-semialdehyde aminotransferase protein were produced. This was achieved using a cassette composed of a full-length Medicago sative cDNA under the control of the cauliflower mosaic virus 35S promoter. The results revealed distinct impacts of GSA activity on photosynthesis rate and growth in GSA over expression tobacco plants. In transgenic plants with increased GSA activity, an increase in soluble and insoluble sugars accumulation was evident. Total biomass, leaf area, plant height and internode 3-4 were increased in GSA sense plants, compared with equivalent wild-type tobacco plants. Moreover, transgenic tobacco plants with increased GSA activity exhibit higher levels of 5-aminolevulinic acid (ALA) accumulation and increased in content of chlorophyll and carotenoids pigments. Collectively, our data suggest that higher level of GSA activity gives an advantage to photosynthesis, growth in tobacco plants. This work also provides a case study that an individual enzyme in the biosynthesis of chlorophyll pathway may serve as a useful target for genetic engineering to improve photosynthesis and growth in plants.\n\nHighlightOverexpression of glutamate-semialdehyde aminotransferase (GSA) increase photosynthetic capacity, growth in tobacco.

plant biology↗

bioRxiv2019

ARGONAUTE5 Mediates Fine-Tuning of Vegetative-to-Reproductive Phase Transition Through Its Interaction with miR156 in Arabidopsis

Vegetative-to-reproductive phase change is a finely tuned process in plants, largely controlled by the age-regulated microRNA156 (miR156), which functions by suppressing the transcripts of SQUAMOSA-PROMOTER BINDING LIKE (SPL) transcription factors. ARGONAUTE proteins (AGO) are essential effectors of miRNA-mediated gene regulation. However, which AGO(s) mediate(s) the control of flowering time remains unclear. Here, we demonstrate a role for AGO5 in vegetative-to-reproductive phase transition through the modulation of SPL transcription factors. We show that AGO5 interacts physically and functionally with miR156 and that ago5 mutants present an early flowering phenotype in Arabidopsis. Furthermore, in ago5 mutants, the repression of flowering caused by miR156 overexpression is largely reversed, whereas leaf morphology remains unaffected. Our results thus indicate a specific role for AGO5 in mediating miR156 activity in meristematic, but not vegetative, tissue. As such, our data suggest a spatiotemporal regulation of the miR156 aging pathway, mediated through different AGO proteins in different tissues.

plant biology↗

bioRxiv2019

A bacterial effector protein prevents MAPK-mediated phosphorylation of SGT1 to suppress plant immunity

Nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins function as sensors that perceive pathogen molecules and activate immunity. In plants, the accumulation and activation of NLRs is regulated by SUPPRESSOR OF G2 ALLELE OF skp1 (SGT1). In this work, we found that an effector protein named RipAC, secreted by the plant pathogen Ralstonia solanacearum, associates with SGT1 to suppress NLR-mediated SGT1-dependent immune responses, including those triggered by another R. solanacearum effector, RipE1. RipAC does not affect the accumulation of SGT1 or NLRs, or their interaction. However, RipAC inhibits the interaction between SGT1 and MAP kinases, and the phosphorylation of a MAPK target motif in the C-terminal domain of SGT1. Such phosphorylation is enhanced upon activation of immune signaling, leads to the release of the interaction between SGT1 and NLRs, and contributes to the activation of NLR-mediated responses. Additionally, SGT1 phosphorylation contributes to resistance against R. solanacearum, and this is particularly evident in the absence of RipAC. Our results shed light onto the mechanism of activation of NLR-mediated immunity, and suggest a positive feedback loop between MAPK activation and SGT1-dependent NLR activation.

plant biology↗