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Results for “Plant Biology”

Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

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At least 1,135 records · Page 63Linked to original sources

bioRxiv2019

Elevated CO2 induces age-dependent restoration of growth and metabolism in gibberellin-deficient plants

Main conclusion The effect of elevated [CO2] on the growth of tomato plants with reduced GA content is influenced by developmental stage. The increase of carbon dioxide (CO2) in the atmosphere during the last decades has aroused interest in the function of this gas in the growth and development of plants. Despite the known association between elevated CO2 concentration ([CO2]) and plant growth, its effects in association with gibberellin (GA), plant hormone that regulates de major aspects of plant growth, are still poorly understood. Therefore, we evaluated the effect of elevated [CO2] on growth and primary metabolism in tomato plants with drastic reduction in GA content (gib-1) at two different growth stages (21 and 35 days after germination, dag). Disruption on growth, photosynthetic parameters and primary metabolism were restored when gib-1 plants were transferred to elevated [CO2] at 21 dag. Elevated [CO2] also stimulated growth and photosynthetic parameters in Wild type (WT) plants at 21 dag, however, minor changes were observed in the level of primary metabolites. At 35 dag, elevated [CO2] did not stimulate growth in WT plants and gib-1 mutants showed their characteristic stunted growth phenotype.

plant biology↗

bioRxiv2019

An evolutionarily conserved mechanism for production of secondary meristems in land plants

A variety of plants in diverse taxa can reproduce asexually via vegetative propagation, in which clonal propagules with new meristem(s) are generated directly from vegetative organs. A basal land plant, Marchantia polymorpha, develops clonal propagules, gemmae, in a specialized receptacle, gemma cup. Here we report an R2R3-MYB transcription factor, designated GEMMA CUP-ASSOCIATED MYB 1 (GCAM1), which is an essential regulator of gemma cup development in M. polymorpha. Although gemma cups are a characteristic gametophyte organ for vegetative reproduction in a taxonomically restricted group of liverwort species, phylogenetic and interspecific complementation analyses supported the orthologous relationship of GCAM1 to regulatory factors for axillary meristem formation, e.g. Arabidopsis RAXs and tomato Blind, in angiosperm sporophytes. The present findings in M. polymorpha suggest an ancient acquisition of a regulatory mechanism for production of secondary meristems, and the use of the mechanism for diverse developmental programs during land plant evolution.

plant biology↗

bioRxiv2019

Targeted mutagenesis of the SUMO protease, Overly Tolerant to Salt1 in rice through CRISPR/Cas9-mediated genome editing reveals a major role of this SUMO protease in salt tolerance.

SUMO proteases are encoded by a large gene family in rice and are a potential source of specificity within the SUMO system that is responding to different environmental cues. We previously demonstrated a critical role of OsOTS class of SUMO proteases in salt and drought stress in rice by silencing several family members collectively via RNAi methods. However, to date it has not been possible to assign a role to specific family members due to limitations of RNAi mediated off target silencing across several members of the gene family. The clustered regularly interspaced short palindromic repeats (CRISPR)-associated endonuclease 9 (CRISPR/Cas9) system has emerged as a promising technology for specific gene editing in crop plants. Here, we demonstrate targeted mutagenesis of OsOTS1 in rice using the CRISPR/Cas9 gene editing system in the rice cultivar Kitaake. Guide RNA mediated mutations in OsOTS1 was highly efficient with almost 95% of T0 transgenics showing the desired effect with no off-target mutations. The OsOTS1 mutations observed in T0 generation were heritable in subsequent generations. OsOTS1 CRISPR lines show enhanced sensitivity to salt with reduced root and shoot biomass indicating that OsOTS1 has a major role in salt stress tolerance in rice. This unexpected finding indicates that precise and effective genome editing can be used to characterise specificity within the SUMO system in rice.

plant biology↗

bioRxiv2019

Molecular signaling involved in immune system activation against root-knot nematodes by bio-control agents in tomato plants

The expression of key defense genes was detected in roots and leaves of tomato plants until the 12th day after treatments with a mixture of beneficial bio-control agents (BCAs), as soil-drenches. The expression of the same genes was monitored in pretreated plants at the 3rd and 7th day since the inoculation with the root-knot nematode Meloidogyne incognita. Genes dependent on SA-signaling, such as the Pathogenesis Related Genes, PR1, PR3, and PR5, were systemically over-expressed at the earliest stages of BCA-root interaction. BCA pre-treatment primed plants against root-knot nematodes. The expression of PR-genes and of the gene encoding for the enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO), which catalyzes the last step of ethylene biosynthesis, was systemically enhanced after nematode inoculation in primed plants. Defense related enzyme activities, such as endochitinase and glucanase, were higher in roots of BCA-treated than in those of untreated plants, as well. On the contrary, the expression of genes dependent on JA/ET-signaling, such as Jasmonate Ethylene Response Factor 3 (JERF3), did not increase after nematode inoculation in primed plants. The antioxidant system, as indicated by catalase gene expression and ascorbate peroxidase activity, was repressed in infected colonized roots. Therefore, Systemic Acquired Resistance (SAR), and not Induced Systemic Resistance (ISR), is proposed as the molecular signaling that is activated by BCA priming at the earliest stages of root-nematode interaction. Such BCA-induced activation of the plant immune system did not directly act against nematode motile juveniles penetrating and moving inside the roots. It resulted in a drastically decreased number of sedentary individuals and, then, in an augmented ability of the plants to contrast feeding site building by invasive juveniles.

plant biology↗

bioRxiv2019

Structural and biochemical studies of an NB-ARC domain from a plant NLR immune receptor

Plant NLRs are modular immune receptors that trigger rapid cell death in response to attempted infection by pathogens. A highly conserved nucleotide-binding domain shared with APAF-1, various R-proteins and CED-4 (NB-ARC domain) is proposed to act as a molecular switch, cycling between ADP (repressed) and ATP (active) bound forms. Studies of plant NLR NB-ARC domains have revealed functional similarities to mammalian homologues, and provided insight into potential mechanisms of regulation. However, further advances have been limited by difficulties in obtaining sufficient yields of protein suitable for structural and biochemical techniques. From protein expression screens in Escherichia coli and Sf9 insect cells, we defined suitable conditions to produce the NB-ARC domain from the tomato NLR NRC1. Biophysical analyses of this domain showed it is a folded, soluble protein. Structural studies revealed the NRC1 NB-ARC domain had co-purified with ADP, and confirmed predicted structural similarities between plant NLR NB-ARC domains and their mammalian homologues.

plant biology↗

bioRxiv2019

Latent Space Phenotyping: Automatic Image-Based Phenotyping for Treatment Studies

Association mapping studies have enabled researchers to identify candidate loci for many important environmental resistance factors, including agronomically relevant resistance traits in plants. However, traditional genome-by-environment studies such as these require a phenotyping pipeline which is capable of accurately and consistently measuring stress responses, typically in an automated high-throughput context using image processing. In this work, we present Latent Space Phenotyping (LSP), a novel phenotyping method which is able to automatically detect and quantify response to treatment directly from images. Using two synthetically generated image datasets, we first show that LSP is able to successfully recover the simulated QTL in both simple and complex synthetic imagery. We then demonstrate an example application of an interspecific cross of the model C4 grass Setaria. We propose LSP as an alternative to traditional image analysis methods for phenotyping, enabling association mapping studies without the need for engineering complex image processing pipelines.

plant biology↗

bioRxiv2019

Brassinosteroids control gravitropism by changing cellulose orientation and mannan content in Arabidopsis hypocotyls

The force of gravity is a constant environmental factor. Plant shoots respond to gravity through negative gravitropism and gravity resistance. These responses are essential for plants to direct the growth of aerial organs away from the soil surface after germination and to keep an upright posture above ground. We took advantage of the effect of brassinosteroids on the two types of graviresponses in Arabidopsis thaliana hypocotyls to disentangle functions of cell wall polymers during etiolated shoot growth. The ability of etiolated Arabidopsis seedlings to grow upwards was suppressed in the presence of 24-epibrassinolide (EBL) but enhanced in the presence of brassinazole (BRZ), an inhibitor of brassinosteroid biosynthesis. These effects were accompanied by changes in cell wall mechanics and composition. Cell wall biochemical analyses and confocal microscopy of the cellulose-specific pontamine S4B dye revealed that the EBL and BRZ treatments correlated with changes in cellulose fibre organization and mannan content. Indeed, a longitudinal re-orientation of cellulose fibres supported upright growth whereas the presence of mannans reduced gravitropic bending. The negative effect of mannans on gravitropism is a new function for this class of hemicelluloses, highlighting evolutionary adaptations by which aquatic ancestors of terrestrial plants colonized land.

plant biology↗

bioRxiv2019

Characterizing grapevine (Vitis spp.) inflorescence architecture using X-ray imaging: implications for understanding cluster density

We characterized grapevine inflorescence architecture (the rachis and all branches without berries) to describe variation among 10 wild Vitis species, assess phylogenetic signals underlying inflorescence architecture traits, and interpret this variation in the context of breeding objectives. Three-dimensional X-ray tomography scans of grapevine inflorescences were used to measure geometric traits and inflorescence topology using persistent homology, a mathematical approach that can comprehensively measure and compare shapes. We simulated potential space available for berry growth within a given inflorescence architecture by evaluating expanding spheres attached to pedicels, referred to as "berry potential." Lastly, we performed phylogenetic analysis and mapped trait variation. We detected wide variation in inflorescence architecture features among Vitis species. Hierarchical clustering and correlation analyses revealed relationships among traits. Multivariate analyses identify traits contributing the most to variation and distinguish between species with high accuracy. Phylogenetic analyses revealed 12 morphological traits with strong phylogenetic signal. Morphometric analysis uncovered novel differences in inflorescence architecture among clades and between Vitis species. Cluster density is an important trait for assessing crop quality and forecasting yield; analyses presented here can be used to tease apart subtle, heritable features and environmental influences on this major agronomic trait.

plant biology↗

bioRxiv2019

mRNA adenosine methylase (MTA) deposits m6A on pri-miRNAs to modulate miRNA biogenesis in Arabidopsis thaliana

m6A, one of the most abundant mRNA modifications, has been associated with various metabolic processes in plants. Here we show that m6A also plays a role in miRNA biogenesis in Arabidopsis thaliana. Significant reductions in plant m6A/MTA levels results in lower accumulation of miRNAs whereas pri-miRNA levels tend to be higher in such plants. m6A-IP Seq and MTA-GFP RIP were used to show that many pri-miRNAs are m6A methylated and are bound by MTA, further demonstrating that pri-miRNAs can also be substrates for m6A methylation by MTA. We report that MTA interacts with RNA Pol II, supporting the assumption that m6A methylation is a co-transcriptional process, and also identify TGH, a known miRNA biogenesis related protein, as a novel protein that interacts with MTA. Finally, reduced levels of miR393b may partially explain the strong auxin insensitivity seen in Arabidopsis plants with reduced m6A levels.

plant biology↗

bioRxiv2019

Arabidopsis mlo3 mutant plants exhibit spontaneous callose deposition and signs of early leaf senescence

The family of Mildew resistance Locus O (MLO) proteins is best known for its profound effect on the outcome of powdery mildew infections: when the appropriate MLO protein is absent, the plant is fully resistant to otherwise virulent powdery mildew fungi. However, most members of the MLO protein family remain functionally unexplored. Here, we investigate Arabidopsis thaliana MLO3, the closest relative of AtMLO2, AtMLO6 and AtMLO12, which are the Arabidopsis MLO genes implicated in the powdery mildew interaction. The co-expression network of AtMLO3 suggests association of the gene with plant defense-related processes such as salicylic acid homeostasis. Our extensive analysis shows that mlo3 mutants are unaffected regarding their infection phenotype upon challenge with the powdery mildew fungi Golovinomyces orontii and Erysiphe pisi, the oomycete Hyaloperonospora arabidopsidis, and the bacterial pathogen Pseudomonas syringae (the latter both in terms of basal and systemic acquired resistance), indicating that the protein does not play a major role in the response to any of these pathogens. However, mlo3 genotypes display spontaneous callose deposition as well as signs of early senescence in six-or seven-week-old rosette leaves in the absence of any pathogen challenge, a phenotype that is reminiscent of mlo2 mutant plants. We hypothesize that de-regulated callose deposition in mlo3 genotypes is the result of a subtle transient aberration of salicylic acid-jasmonic acid homeostasis during development.

plant biology↗

bioRxiv2019

Mechanisms Underlying the Enhanced Biomass and Abiotic Stress Tolerance Phenotypes of an Arabidopsis MIOX Over expresser

Myo-inositol oxygenase (MIOX) is the first enzyme in the inositol route to ascorbate (L-ascorbic acid, AsA, vitamin C). We have previously shown that Arabidopsis plants constitutively expressing MIOX have elevated foliar AsA content and displayed enhanced growth rate, biomass accumulation, and increased tolerance to multiple abiotic stresses. In this work, we used a combination of transcriptomics, chromatography, microscopy, and physiological measurements to gain a deeper understanding of the underlying mechanisms mediating the phenotype of the AtMIOX4 line. Transcritpomic analysis revealed increased expression of genes involved in auxin synthesis, hydrolysis, transport, and metabolism, which are supported by elevated auxin levels both in vitro and in vivo, and confirmed by assays demonstrating their effect on epidermal cell elongation in the AtMIOX4 over-expresser plants. Additionally, we detected up-regulation of transcripts involved in photosynthesis that was validated by increased efficiency of the photosystem II and proton motive force. We also found increased expression of amylase leading to higher intracellular glucose levels. Multiple gene families conferring plants tolerance to cold, water limitation, and heat stresses were found to be elevated in the AtMIOX4 line. Interestingly, the high AsA plants also displayed up-regulation of transcripts and hormones involved in defense including jasmonates, defensin, glucosinolates, and transcription factors that are known to be important for biotic stress tolerance. These results overall indicate that elevated levels of auxin and glucose, and enhanced photosynthetic efficiency in combination with up-regulation of abiotic stresses response genes underly the higher growth rate and abiotic stresses tolerance phenotype of the AtMIOX4 over-expressers.

plant biology↗

bioRxiv2019

PRH1 mediates ARF7-LBD dependent auxin signaling to regulate lateral root development in Arabidopsis thaliana

The development of lateral roots in Arabidopsis thaliana is strongly dependent on signaling directed by the AUXIN RESPONSE FACTOR7 (ARF7), which in turn activates LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors (LBD16, 18, 29 and 33). Here, the product of PRH1, a PR-1 homolog annotated previously as encoding a pathogen-responsive protein, was identified as a target of ARF7-mediated auxin signaling and also as participating in the development of lateral roots. PRH1 was shown to be strongly induced by auxin treatment, and plants lacking a functional copy of PRH1 formed fewer lateral roots. The transcription of PRH1 was controlled by the binding of both ARF7 and LBDs to its promoter region. An interaction was detected between PRH1 and GATA23, a protein which regulates cell identity in lateral root founder cells. Author SummaryIn Arabidopsis thaliana AUXIN RESPONSE FACTOR7 (ARF7)-mediated auxin signaling plays a key role in lateral roots (LRs) development. The LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors (LBD16, 18, 29 and 33) act downstream of ARF7-mediated auxin signaling to control LRs formation. Here, the PR-1 homolog PRH1 was identified as a novel target of both ARF7 and LBDs (especially the LBD29) during auxin induced LRs formation, as both ARF7 and LBDs were able to bind to the PRH1 promoter. More interestingly, PRH1 has a physical interaction with GATA23, which has been also reported to be up-regulated by auxin and influences LR formation through its regulation of LR founder cell identity. Whether the interaction between GATA23 and PRH1 affects the stability and/or the activity of either (or both) of these proteins remains an issue to be explored. This study provides improves new insights about how auxin regulates lateral root development.

plant biology↗

bioRxiv2019

EXOCYST70A3 controls root system depth in Arabidopsis via the dynamic modulation of auxin transport

Root system architecture (RSA), the distribution of roots in soil, plays a major role in plant survival. RSA is shaped by multiple developmental processes that are largely governed by the phytohormone auxin, suggesting that auxin regulates responses of roots that are important for local adaptation. However, auxin has a central role in numerous processes and it is unclear which molecular mechanisms contribute to the variation in RSA for environmental adaptation. Using natural variation in Arabidopsis, we identify EXOCYST70A3 as a modulator of the auxin system that causes variation in RSA by acting on PIN4 protein distribution. Allelic variation and genetic perturbation of EXOCYST70A3 leads to alteration of root gravitropic responses, resulting in a different RSA depth profile and drought resistance. Overall our findings suggest that the local modulation of the pleiotropic auxin pathway can gives rise to distinct root system architectures that can be adaptive in specific environments.

plant biology↗

bioRxiv2019

Big root approximation of site-scale vegetation water uptake

Land surface model (LSM) predictions of soil moisture and transpiration under water-limited conditions suffer from biases due to a lack of mechanistic process description of vegetation water uptake. Here, I derive a big root approach from the porous pipe equation for root water uptake and compare its predictions of soil moistures during the 2010 summer drought at the Wind River Crane site to two previously used Ohms law analogue plant hydraulic models. Structural error due to inadequate representation of root system architecture (RSA) in both Ohms law analogue models yields significant and predictable moisture biases. The big root model greatly reduces these as it better represents RSA effects on pressure gradients and flows within the roots. It represents a major theoretical advance in understanding vegetation water limitation at site scale with potential to improve LSM predictions of soil moisture, temperature and surface heat, water, and carbon fluxes.

plant biology↗

bioRxiv2019

Cytoskeleton dynamics control early events of lateral root initiation in Arabidopsis

How plant cells re-establish differential growth to initiate organs is poorly understood. Morphogenesis of lateral roots relies on the tightly controlled radial expansion and asymmetric division of founder cells. The cellular mechanisms that license and ensure these features are unknown. Here, we quantitatively analyse F-actin and microtubule dynamics during LR initiation. Using mutants, pharmacological and tissue-specific genetic perturbations, we show that dynamic reorganisation of both microtubule and F-actin networks is required for the asymmetric expansion of the founder cells. This cytoskeleton remodelling intertwine with auxin signalling in the pericycle and endodermis in order for founder cells to acquire a basic polarity required for initiating LR development. Our results reveal the conservation of cell remodelling and polarisation strategies between the Arabidopsis zygote and lateral root founder cells. We propose that coordinated, auxin-driven reorganisation of the cytoskeleton licenses asymmetric cell growth and divisions during embryonic and post-embryonic organogenesis. HIGHLIGHTSO_LIFailure for lateral root founder cells to undergo asymmetric radial expansion before division, leads to aberrant organ formation. C_LIO_LICortical microtubules arrays reorganise to facilitate this asymmetric expansion and F-actin the asymmetric division. C_LIO_LICytoskeletal reorganisation depends on auxin signalling. C_LIO_LINew genetic tools allow to perturb microtubules or actin in an inducible and cell-type specific manner. C_LI

plant biology↗

bioRxiv2019

What Drives Symbiotic Calcium Signalling In Legumes? Insights And Challenges Of Imaging

We review the contribution of bioimaging in building a coherent understanding of Ca2+ signalling during legume-bacteria symbiosis. Currently, two different calcium signals are believed to control key steps of the symbiosis: a Ca2+ gradient at the tip of the legume root hair is involved in the development of an infection thread, while nuclear Ca2+ oscillations, the hallmark signal of this symbiosis, controls the formation of the root nodule, where bacteria fix nitrogen. Additionally, different Ca2+ spiking signatures have been associated with specific infection stages. Bioimaging is intrinsically a cross-disciplinary area that requires integration of image recording, processing and analysis. We use experimental examples to critically evaluate previously established conclusions and draw attention to challenges caused by the varying nature of the signal-to-noise ratio in live imaging. We hypothesise that nuclear Ca2+ spiking is a wide-range signal involving the entire root hair, and that Ca2+ signature may be related to cytoplasmic streaming.

plant biology↗

bioRxiv2019

An oomycete RXLR effector triggers antagonistic plant hormone crosstalk to suppress host immunity

Understanding the mechanisms through which pathogens alter plant cell networks is essential for understanding plant-pathogen interactions and will inform efforts to reduce crop diseases. Oomycetes secrete diverse effector proteins into plant cells. The mechanisms through which these effectors promote virulence are largely unknown. We show that the HaRxL10 effector protein from the Arabidopsis thaliana pathogen Hyaloperonospora arabidopsidis (Hpa) targets a transcriptional repressor (JAZ3) involved in jasmonic acid (JA) signalling. This manipulation activates a regulatory cascade that inhibits salicylic acid (SA) signalling, which normally restricts Hpa infection. This virulence mechanism is functionally equivalent to but mechanistically distinct from activation of the antagonistic JA-SA hormone crosstalk by the bacterial JA-mimicking toxin coronatine and by bacterial Type III effectors. These results reveal a key role for JAZ3 in plant immunity and emphasize that JA-SA crosstalk is an Achilles heel in the plant immune system, vulnerable to manipulation by diverse microbes.

plant biology↗

bioRxiv2019

Enzyme kinetics of tobacco Rubisco expressed in Escherichia coli varies depending on the small subunit composition

AbstractRubisco catalyzes the first step in carbon fixation and has been a strategic target to improve photosynthetic efficiency. In plants, Rubisco is a complex made up of eight large subunits encoded by a chloroplast gene, rbcL, and eight small subunits expressed from a nuclear gene family and targeted to chloroplast stroma. Biogenesis of Rubisco in plants requires a chaperonin system composed of Cpn60, Cpn60{beta} and Cpn20, which helps fold the large subunit, and multiple chaperones including RbcX, Raf1, Raf2 and BSD2, which help the dimerization of the folded large subunits and subsequent assembly with the small subunits into L8S8 holoenzymes. A recent study successfully assembled functional Arabidopsis Rubisco in Escherichia coli by co-expressing the two subunits with Arabidopsis chaperonins and chaperones (Aigner et al., 2017). In this study, we modified the expression vectors used in that study and adapted them to express tobacco Rubisco by replacing the Arabidopsis genes with tobacco ones. Next, we surveyed the small subunits present in tobacco, co-expressed each with the large subunit and successfully produced active tobacco enzymes composed of different small subunits in E. coli. These enzymes produced in E. coli have carboxylation kinetics very similar to that of the native tobacco Rubisco. We also produced tobacco Rubisco with a recently discovered trichome small subunit in E. coli and found that it has a higher catalytic rate and a lower CO2 affinity compared to the enzymes with other small subunits. Our improvements in the E. coli Rubisco expression system will allow us to probe features of both the chloroplast and nuclear-encoded subunits of Rubisco that affect its catalytic rate and CO2 specificity.

plant biology↗