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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 Read source abstracts and check manuscript versions; preprints are not peer reviewed.

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bioRxiv2018

Identification of novel RNA viruses associated to bird’s-foot trefoil (Lotus corniculatus)

Birds-foot trefoil (Lotus corniculatus) is a nutritious forage crop, employed for livestock foraging around the world. Here, we report the identification and characterization of two novel viruses associated with birds-foot trefoil. Virus sequences with affinity to enamoviruses (ssRNA (+); Luteoviridae; Enamovirus) and nucleorhabdoviruses (ssRNA (-); Rhabdoviridae; Nucleorhabdovirus) were detected in L. corniculatus transcriptome data. The tentatively named birds-foot trefoil associated virus 1 (BFTV-1) genome organization is characterized by 13,626 nt long negative-sense ssRNA. BFTV-1 presents in its antigenome orientation six predicted gene products in the canonical order 3'-N-P-P3-M-G-L-5'. The proposed birds-foot trefoil associated virus 2 (BFTV-2) 5,736 nt virus sequence presents a typical 5'-PO-P1-2-IGS-P3-P5-3' enamovirus genome structure. Phylogenetic analysis suggests that BFTV-1 is closely related to Datura yellow vein nucleorhabdovirus, and that BFTV-2 clusters into a monophyletic cluster of legumes-associated enamoviruses. This sub-clade of highly related and co-divergent legume associated viruses provides insights on the evolutionary history of the enamoviruses. The bioinformatic reanalysis of SRA libraries deposited in the NCBI database constitutes an emerging approach to the discovery of novel plant viruses which should be important for both quarantine purposes and disease management.

plant biology↗

bioRxiv2018

Genetic Diversity Patterns and Domestication Origin of Soybean

Understanding diversity and evolution of a crop is an essential step to implement a strategy to expand its germplasm base for crop improvement research. Samples intensively collected from Korea, which is a small but central region in the distribution geography of soybean, were genotyped to provide sufficient data to underpin genome-wide population genetic questions. After removing natural hybrids and duplicated or redundant accessions, we obtained a non-redundant set comprising 1,957 domesticated and 1,079 wild accessions to perform population structure analyses. Our analysis demonstrates that while wild soybean germplasm will require additional sampling from diverse indigenous areas to expand the germplasm base, the current domesticated soybean germplasm is saturated in terms of genetic diversity. We then showed that our genome-wide polymorphism map enabled us to detect genetic loci underling flower color, seed-coat color, and domestication syndrome. A representative soybean set consisting of 194 accessions were divided into one domesticated subpopulation and four wild subpopulations that could be traced back to their geographic collection areas. Population genomics analyses suggested that the monophyletic group of domesticated soybeans was originated in eastern Japan. The results were further substantiated by a phylogenetic tree constructed from domestication-associated single nucleotide polymorphisms identified in this study.

plant biology↗

bioRxiv2018

Speed breeding in growth chambers and glasshouses for crop breeding and model plant research

1.To meet the challenge of feeding a growing population, breeders and scientists are continuously looking for ways to increase genetic gain in crop breeding. One way this can be achieved is through \"speed breeding\" (SB), which shortens the breeding cycle and accelerates research studies through rapid generation advancement. The SB method can be carried out in a number of ways, one of which involves extending the duration of a plants daily exposure to light (photoperiod) combined with early seed harvest in order to cycle quickly from seed to seed, thereby reducing the generation times for some long-day (LD) or day-neutral crops. Here we present glasshouse and growth chamber-based SB protocols with supporting data from experimentation with several crop species. These protocols describe the growing conditions, including soil media composition, lighting, temperature and spacing, which promote rapid growth of spring and winter bread wheat, durum wheat, barley, oat, various members of the Brassica family, chickpea, pea, grasspea, quinoa and the model grass Brachypodium distachyon. Points of flexibility within the protocols are highlighted, including how plant density can be increased to efficiently scale-up plant numbers for single seed descent (SSD) purposes. Conversely, instructions on how to perform SB on a small-scale by creating a benchtop SB growth cabinet that enables optimization of parameters at a low cost are provided. We also outline the procedure for harvesting and germinating premature wheat, barley and pea seed to reduce generation time. Finally, we provide troubleshooting suggestions to avoid potential pitfalls.

plant biology↗

bioRxiv2018

Novel cytonuclear combinations modify Arabidopsis seed physiology and vigor

The influence of intraspecific variation in cytoplasmic genomes and cytonuclear interactions on key seed traits that can impact adaptation and agriculture has not been thoroughly explored, so far. Here, dormancy, germination performance and longevity of seeds have been assessed in Arabidopsis plants with novel cytonuclear combinations that disrupt coadaptation between natural variants of nuclear and cytoplasmic genomes. Although all three traits were affected by cytonuclear reshuffling, the sensitivity of seed traits to cytoplasmic change was dependent on the nuclear background. Both deleterious and, more surprisingly, favorable effects of novel cytonuclear combinations (in comparison with the nuclear parent) were observed, suggesting suboptimal genetic combinations exist in natural populations for these traits. Significant changes on dormancy and germination performance due to specific cytonuclear interacting combinations mainly occurred in opposite directions, in accordance with the previously proposed dormancy continuum. Consistently, reduced sensitivity to exogenous ABA and faster endogenous ABA decay during germination were observed in a novel cytonuclear combination that also exhibited enhanced longevity and better germination performance, compared to its natural nuclear parent. Cytoplasmic genomes, therefore, represent an additional resource of natural variation for breeding seed vigor traits.\n\nIssue sectionGrowth and development\n\nHighlightNatural variation in Arabidopsis organelles and cytonuclear interactions influence seed dormancy, longevity and germination performance. Enhanced seed vigor was obtained through the creation of novel cytonuclear combinations.

plant biology↗

bioRxiv2018

Influence of Shea Tree (Vitellaria Paradoxa) on Maize and Soybean Production

Vitellaria paradoxa provides many benefits to farmers within the Shea belt. However, increased threats to it necessitate its conservation, and one common approach is the practice of agroforestry. A number of studies have shown that Shea tree has influence on crop production, and yet, some of these studies were done using single season experiments or bioassays using mature Shea tree components. In this study, the seasonal influence of young and mature Shea trees on Maize and Soybean yields was investigated using field experiments in Otuke district of northern Uganda, where, Shea tree parklands are dominant and Maize and Soybean are used for food security and income. Our results show that there are differential responses of maize and soybean yield to rainy seasons and physiological differences of Vitellaria paradoxa treatment. We find yield reduction for maize more pronounced than yield reduction for soybeans under different Shea plants (Mature and Young) and for the two rainy seasons. We attribute the difference to the differential maize and soybean responses to Vitellaria paradoxa shading and its differential allelopathic inhibition of these crops. We recommend that Soybeans should be preferred to maize when planting under Shea canopy.

plant biology↗

bioRxiv2018

MuSCA: a multi-scale model to explore carbon allocation in plants

Background and aimsCarbon allocation in plants is usually represented at a specific spatial scale, peculiar to each model. This makes the results obtained by different models, and the impact of their scale of representation, difficult to compare. In this work we developed a Multi Scale Carbon Allocation model (MuSCA) that can be applied at different, user-defined, topological scales of a plant, and used to assess the impact of each spatial scale on simulated results and computation time.\n\nMethodsModel multi-scale consistency and behavior were tested by applications on three realistic apple tree structures. Carbon allocation was computed at five spatial scales, spanning from the metamer (the finest scale, used as a reference) up to 1st order branches, and for different values of a sap friction coefficient. Fruit dry mass increments were compared across spatial scales and with field data.\n\nKey ResultsThe model showed physiological coherence in representing competition for carbon assimilates. Results from intermediate values of the friction parameter best fitted the field data. For these, fruit growth simulated at the metamer scale (considered as a reference) differed from about 1% at growth unit scale up to 35% at first order branch scale. Generally, the coarser the spatial scale the more fruit growth diverged from the reference and the lower the obtained within-tree fruit growth variability. Coherence in the carbon allocated across scales was also differently impacted, depending on the tree structure considered. Decreasing the topological resolution reduced computation time up to four orders of magnitude.\n\nConclusionsMuSCA revealed that the topological scale has a major influence on the simulation of carbon allocation, suggesting that this factor should be carefully evaluated when using different carbon allocation models or comparing their results. Trades-off between computation time and prediction accuracy can be evaluated by changing topological scales.

plant biology↗

bioRxiv2018

Mild drought induces phenotypic and DNA methylation plasticity but no transgenerational effects in Arabidopsis

Whether environmentally induced changes in phenotypes can be heritable is a topic with revived interest, in part because of observations in plants that heritable trait variation can occur without DNA sequence mutations. This other system of inheritance, called transgenerational epigenetics, typically involves differences in DNA methylation that are stable across multiple generations. However, it remains unknown if such a system responds to environmental changes and if it could therefore provide a rapid way for plants to generate adaptive heritable phenotypic variation. Here, we used a well-controlled phenotyping platform and whole-genome bisulfite sequencing to investigate potential heritable effects of mild drought applied over two successive generations in Arabidopsis thaliana. Plastic phenotypic responses were observed in plants exposed to drought. After an intervening generation without stress, descendants of stressed and non-stressed plants were phenotypically indistinguishable, except for very few trait-based parental effects, and irrespective of whether they were grown in control conditions or under water deficit. Moreover, while mild drought induced changes to the DNA methylome of exposed plants, DNA methylation variants were not inherited. These findings add to the growing body of evidence indicating that transgenerational epigenetics is not a common response of plants to environmental changes.

plant biology↗

bioRxiv2018

Diallel Analysis for Morphological and Biochemical Traits in Tomato Cultivated Under the Influence of Tomato Leaf Curl Virus

Eloquent information about the genetic basis of inheritance is important for any breeding program. Therefore, a diallel study was conducted under the influence of tomato leaf curl virus (TLCV) disease, using the eleven advanced lines of tomato. Firstly, the information regarding percent disease index (PDI) was determined via artificial screening with viruliferous whiteflies. Later, these lines were crossed in half diallel mating design to produce fifty-five one-way hybrids. These hybrids and parental genotypes were evaluated for seven morphological and three biochemical traits under open field conditions. Using the Griffing approach (Method II and Model I) basis of inheritance of traits were determined. Also, a Bayesian model was applied to the total yield descriptor. Correlations data indicated that total yield was not correlated with any other trait. The significant general combining ability (GCA) and specific combining ability (SCA) values indicates exploitable genetic variation. The broad-sense heritability values were larger than narrow-sense heritability, showing that selection will be efficient for the improvement of these traits. Hybrid combinations H23, H42 and H49 can be considered efficient for the selection of multiple traits, including yield. Overall, this study provides a useful information regarding the genetics of important traits of tomato under TLCV infestation.

plant biology↗

bioRxiv2018

Nocturnal expression of Crassulacean acid metabolism (CAM) genes predates the origin of CAM in the genus Yucca.

HighlightAlthough large differences in metabolism exist between C3 and CAM species, we find that many CAM genes have shared expression patterns regardless of photosynthetic pathway, suggesting ancestral propensity for CAM.\n\nAbstractCrassulacean acid metabolism (CAM) is a carbon-concentrating mechanism that has evolved numerous times across flowering plants and is thought to be an adaptation to water limited environments. CAM has been investigated from physiological and biochemical perspectives, but little is known about how plants evolve from C3 to CAM at the genetic or metabolic level. Here we take a comparative approach in analyzing time-course data of C3, CAM, and C3+CAM intermediate Yucca (Asparagaceae) species. RNA samples were collected over a 24-hour period from both well-watered and drought-stressed plants and were clustered based on time-dependent expression patterns. Metabolomic data reveals differences in carbohydrate metabolism and antioxidant response between the CAM and C3 species, suggesting changes to metabolic pathways are important for CAM evolution and function. However, all three species share expression profiles of canonical CAM pathway genes, regardless of photosynthetic pathway. Despite differences in transcript and metabolite profiles between the C3 and CAM species, shared time-structured expression of CAM genes in both CAM and C3 Yucca species suggests ancestral expression patterns required for CAM may have predated its origin in Yucca.

plant biology↗

bioRxiv2018

Alternative splicing and translation play important roles in parallel with transcriptional regulation during rice hypoxic germination

Post-transcriptional mechanisms, including alternative splicing (AS) and alternative translation initiation (ATI), have been used to explain the protein diversity involved in plant developmental processes and stress responses. Rice germination under hypoxia conditions is a classical model system for the study of low oxygen stress. It is known that there is transcriptional regulation during rice hypoxic germination, but the potential roles of AS and ATI in this process are not well understood. In this study, a proteogenomic approach was used to integrate the data from RNA sequencing, qualitative and quantitative proteomics to discover new players or pathways in the response to hypoxia stress. The improved analytical pipeline of proteogenomics led to the identification of 10,253 intron-containing genes, 1,729 of which were not present in the current annotation. Approximately 1,741 differentially expressed AS (DAS) events from 811 genes were identified in hypoxia-treated seeds in comparison to controls. Over 95% of these were not present in the list of differentially expressed genes (DEG). In particular, regulatory pathways such as spliceosome, ribosome, ER protein processing and export, proteasome, phagosome, oxidative phosphorylation and mRNA surveillance showed substantial AS changes under hypoxia, suggesting that AS responses are largely independent of traditional transcriptional regulation. Massive AS changes were identified, including the preference usage of certain non-conventional splice sites and enrichment of splicing factors in the DAS datasets. In addition, using self-constructed protein libraries by 6-frame translation, thousands of novel proteins/peptides contributed by ATI were identified. In summary, these results provide deeper insights towards understanding the underlying mechanisms of AS and ATI during rice hypoxic germination.

plant biology↗

bioRxiv2018

Maize defective kernel5 is a bacterial tamB homolog required for chloroplast envelope biogenesis

Chloroplasts are of prokaryotic origin with a double membrane envelope that separates plastid metabolism from the cytosol. Envelope membrane proteins integrate the chloroplast with the cell, but the biogenesis of the envelope membrane remains elusive. We show that the maize defective kernel5 (dek5) locus is critical for plastid membrane biogenesis. Amyloplasts and chloroplasts are larger and reduced in number in dek5 with multiple ultrastructural defects. We show that dek5 encodes a protein homologous to rice SUBSTANDARD STARCH GRAIN4 (SSG4) and E.coli tamB. TamB functions in bacterial outer membrane biogenesis. The DEK5 protein is localized to the chloroplast envelope with a topology analogous to TamB. Increased levels of soluble sugars in dek5 developing endosperm and elevated osmotic pressure in mutant leaf cells suggest defective intracellular solute transport. Both proteomics and antibody-based analyses show that dek5 chloroplasts have reduced levels of chloroplast envelope transporters. Moreover, dek5 chloroplasts reduce inorganic phosphate uptake with at least an 80% reduction relative to normal chloroplasts. These data suggest that DEK5 functions in plastid envelope biogenesis to enable metabolite transport.

plant biology↗

bioRxiv2018

Response to early drought stress and identification of QTLs controlling biomass production under drought in pearl millet

Pearl millet plays a major role in food security in arid and semi-arid areas of Africa and India. However, it lags behind the other cereal crops in terms of genetic improvement. The recent sequencing of its genome opens the way to the use of modern genomic tools for breeding. Our study aimed at identifying genetic components involved in early drought stress tolerance as a first step toward the development of improved pearl millet varieties or hybrids. A panel of 188 inbred lines from West Africa was phenotyped under early drought stress and well-irrigated conditions. We found a strong impact of drought stress on yield components. This impact was variable between inbred lines. We then performed an association analysis with a total of 392,493 SNPs identified using Genotyping-by-Sequencing (GBS). Correcting for genetic relatedness, genome wide association study identified QTLs for biomass production in early drought stress conditions and for stay-green trait. In particular, genes involved in the sirohaem and wax biosynthesis pathways were found to co-locate with association loci. Our results open the way to use genomic selection to breed pearl millet lines with improved yield under drought stress.

plant biology↗

bioRxiv2018

Re-annotated Nicotiana benthamiana gene models for enhanced proteomics and reverse genetics

Nicotiana benthamiana is an important model organism and representative of the Solanaceae (Nightshade) family. N. benthamiana has a complex ancient allopolyploid genome with 19 chromosomes, and an estimated genome size of 3.1Gb. Several draft assemblies of the N. benthamiana genome have been generated, however, many of the gene-models in these draft assemblies appear incorrect. Here we present a nearly non-redundant database of 42,855 improved N. benthamiana gene-models. With an estimated 97.6% completeness, the new predicted proteome is more complete than the previous proteomes. We show that the database is more sensitive and accurate in proteomics applications, while maintaining a reasonable low gene number. As a proof-of-concept we use this proteome to compare the leaf extracellular (apoplastic) proteome to a total extract of leaves. Several gene families are more abundant in the apoplast. For one of these apoplastic protein families, the subtilases, we present a phylogenetic analysis illustrating the utility of this database. Besides proteome annotation, this database will aid the research community with improved target gene selection for genome editing and off-target prediction for gene silencing.

plant biology↗

bioRxiv2018

Convergent evolution of effector protease recognition by Arabidopsis and barley

The Pseudomonas syringae cysteine protease AvrPphB activates the Arabidopsis resistance protein RPS5 by cleaving a second host protein, PBS1. AvrPphB induces defense responses in other plant species, but the genes and mechanisms mediating AvrPphB recognition in those species have not been defined. Here, we show that AvrPphB induces defense responses in diverse barley cultivars. We show also that barley contains two PBS1 orthologs, that their products are cleaved by AvrPphB, and that the barley AvrPphB response maps to a single locus containing a nucleotide-binding leucine-rich repeat (NLR) gene, which we termed AvrPphB Resistance 1 (Pbr1). Transient co-expression of PBR1 with wild-type AvrPphB, but not a protease inactive mutant, triggered defense responses, indicating that PBR1 detects AvrPphB protease activity. Additionally, PBR1 co-immunoprecipitated with barley and N. benthamiana PBS1 proteins, suggesting mechanistic similarity to detection by RPS5. Lastly, we determined that wheat cultivars also recognize AvrPphB protease activity and contain a Pbr1 ortholog. Phylogenetic analyses showed however that Pbr1 is not orthologous to RPS5. Our results indicate that the ability to recognize AvrPphB evolved convergently, and imply that selection to guard PBS1-like proteins is ancient. Also, the results suggest that PBS1-based decoys may be used to engineer protease effector recognition-based resistance in barley and wheat.

plant biology↗

bioRxiv2018

The wheat Sr22, Sr33, Sr35 and Sr45 genes confer resistance against stem rust in barley

In the last 20 years, stem rust caused by the fungus Puccinia graminis f. sp. tritici (Pgt), has re-emerged as a major threat to wheat and barley cultivation in Africa and Europe. In contrast to wheat with 82 designated stem rust (Sr) resistance genes, barleys genetic variation for stem rust resistance is very narrow with only seven resistance genes genetically identified. Of these, only one locus consisting of two genes is effective against Ug99, a strain of Pgt which emerged in Uganda in 1999 and has since spread to much of East Africa and parts of the Middle East. The objective of this study was to assess the functionality, in barley, of cloned wheat Sr genes effective against Ug99. Sr22, Sr33, Sr35 and Sr45 were transformed into barley cv. Golden Promise using Agrobacterium-mediated transformation. All four genes were found to confer effective stem rust resistance. The barley transgenics remained susceptible to the barley leaf rust pathogen Puccinia hordei, indicating that the resistance conferred by these wheat Sr genes was specific for Pgt. Cloned Sr genes from wheat are therefore a potential source of resistance against wheat stem rust in barley.

plant biology↗

bioRxiv2018

The molecular signatures of compatible and incompatible pollination

Fertilization in flowering plants depends on the early contact and recognition of pollen grains by the receptive papilla cells of the stigma. To identify the associated molecular pathways, we developed a transcriptomic analysis based on single nucleotide polymorphisms (SNPs) present in two Arabidopsis thaliana accessions, one used as female and the other as male. We succeeded in distinguishing 80 % of transcripts according to their parental origins and drew up a catalog of genes whose expression is modified after pollen-stigma interaction. Global analysis of our data reveals that pattern-triggered immunity (PTI)-associated transcripts are upregulated after compatible pollination. From our analysis, we predicted the activation of the Mitogen-activated Protein Kinase 3 on the female side after compatible pollination, which we confirmed through expression and mutant analysis. Our work defines the molecular signatures of compatible and incompatible pollination, highlights the active status of incompatible stigmas, and unravels a new MPK3-dependent cell wall feature associated with stigma-pollen interaction.

plant biology↗

bioRxiv2018

The role of UV-B light on small RNA activity during grapevine berry development

UV-B regulation of anthocyanin biosynthesis in vegetative and grapevine berry tissues has been extensively described. However, its relation with UV-B-regulated microRNAs (miRNAs) has not been addressed before in this species. We explored by deep sequencing of small RNA libraries the developmental dynamics and UV-B effects on miRNAs and associated phased small interfering RNA (phasi-RNAs)-producing loci abundances in in vitro-grown plantlets, in field-grown berry skins of cv. Cabernet Sauvignon, and low- and high UV-B fluence treatments of greenhouse-grown berries at several time points around veraison. We observed by RNA blotting a differential effect of low-versus high-fluence UV-B on miR828 abundances (an effector of anthocyanins and UV-absorbing polyphenolics) across berry development, and identified other miRNAs that correlated with miR828 dynamics. The functional significance of the observed UV-coordinated miRNA responses to UV was supported by degradome evidences of AGO-programmed slicing of mRNAs. Inverse co-expression of the up-regulated miRNAs miR156, miR482, miR530, and miR828 with cognate target gene expressions in response to high fluence UV-B measured by quantitative real-time PCR. These UV-response relationships were also corroborated by analyzing three published transcriptome datasets (berries subjected to UV-C for 1 hr [at pre-veraison], UV-B for five weeks post-veraison, and five red-skinned varieties across four berry development time points). Based on observed significant changes by UV-B on miRNA and derivative phasi-RNA abundances, we propose a regulatory network model of UV responses impacting anti-oxidant and stress-associated polyphenolic compound biosynthesis. In this model high-fluence UV-B increases miR168 (validated in a UV-B small RNA-derived degradome library to target ARGONAUTE1, which spawns phasi-RNAs) and miR530 (targets a novel Plus-3 domain mRNA), while decreasing miR403 abundances (validated to target ARGONAUTE2), thereby coordinating post-transcriptional gene silencing activities by different AGOs. Up-regulation of miR3627/4376 (validated to target Ca2+-transporting ATPase10 that spawns phasi-RNAs) could facilitate anthocyanin accumulation. miR395 and miR399, induced by sulfur and phosphorus starvation in other species (conditions known to trigger anthocyanin accumulation) respond positively to UV-B radiation and are shown to slice cognate targets in grapevine. miR156/miR535 is shown to target SQUAMOSA PROMOTER-BINDING transcription factor genes that potentially regulate the activities of MYB-bHLH-WD40 complexes and thereby anthocyanin biosynthesis. Increases in MYB-bHLH-WD40 TFs could also contribute to the observed up-regulation of miR828 via the conserved and degradome-validated auto-regulatory loop involving miR828/TAS4abc to regulate MYBA6/A7/A5-MYB113-like levels and thereby anthocyanin levels. These results and meta-analysis provide a basis for systems approaches to better understand non-coding RNA functions in response to UV.

plant biology↗

bioRxiv2018

Divergent receptor proteins confer responses to different karrikins in two ephemeral weeds

Wildfires can encourage the establishment of invasive plants by releasing potent germination stimulants, such as karrikins. Seed germination of Brassica tournefortii, a noxious weed of Mediterranean climates, is strongly stimulated by KAR1, which is the archetypal karrikin produced from burning vegetation. In contrast, the closely-related yet non-fire-associated ephemeral Arabidopsis thaliana is unusual because it responds preferentially to KAR2. The /{beta}-hydrolase KARRIKIN INSENSITIVE2 (KAI2) is the putative karrikin receptor identified in Arabidopsis. Here we show that B. tournefortii differentially expresses three KAI2 homologues, and the most highly-expressed homologue is sufficient to confer enhanced responses to KAR1 relative to KAR2 when expressed in Arabidopsis. We further identify two variant amino acid residues near the KAI2 active site that explain the ligand selectivity, and show that this combination has arisen independently multiple times within dicots. Our results suggest that duplication and diversification of KAI2 proteins could confer upon weedy ephemerals and potentially other angiosperms differential responses to chemical cues produced by environmental disturbance, including fire.

plant biology↗