Project description:Root microbiota is important for plant growth and fitness. Little is known about whether and how the assembly of root microbiota may be controlled by epigenetic regulation, which is crucial for gene transcription and genome stability. Here we show that dysfunction of the histone demethylase IBM1 (INCREASE IN BONSAI METHYLATION 1) in Arabidopsis thaliana substantially reshaped the root microbiota, with the majority of the significant amplicon sequence variants (ASVs) being decreased. Transcriptome analyses of plants grown in soil and in sterile growth-medium jointly disclosed salicylic acid (SA)-mediated autoimmunity and production of the defense metabolite camalexin in the ibm1 mutants. Analyses of genome-wide histone modifications and DNA methylation highlighted epigenetic modifications permissive for transcription at several important defense regulators. Consistently, ibm1 mutants showed increased resistance to the pathogen Pseudomonas syringae DC3000 with stronger immune responses. In addition, ibm1 showed substantially impaired plant growth-promotion in response to beneficial bacteria; the impairment was partially mimicked by exogenous application of SA to wild type plants, and by a null mutation of AGP19 that is important for cell expansion and that is repressed with DNA hyper methylation in ibm1. IBM1-dependent epigenetic regulation imposes strong and broad impacts on plant-microbe interactions and thereby shapes the assembly of root microbiota.
Project description:In this study, a cross species hybridization (CSH) approach was used to evaluate whole transcriptome changes during carotenoid accumulation in the storage root of carrot (Daucus carota). Carotenoids are isoprenoid compounds providing red, yellow and orange color to plants. Previous gene expression analyses of carotenoid accumulation in non-model plant species have primarily used a candidate gene approach. Since global transcriptome analyses require extensive genome sequence, in the absence of these genomic resources an alternate approach uses platforms developed for model plant species. To assess transcriptome patterns associated with carotenoid pigmentation in carrot storage root, two carrot sibling inbred lines, B8788, true breeding for orange color and B8750, true breeding for white root color, were hybridized to the Medicago Affymetrix GeneChip microarray.
Project description:Plants and rhizosphere microbes rely closely on each other, with plants supplying carbon to bacteria in root exudates, and bacteria mobilizing soil-bound phosphate for plant nutrition. When the phosphate supply becomes limiting for plant growth, the composition of root exudation changes, affecting rhizosphere microbial communities and microbially-mediated nutrient fluxes. To evaluate how plant phosphate deprivation affects rhizosphere bacteria, Lolium perenne seedlings were root-inoculated with Pseudomonas aeruginosa 7NR, and grown in axenic microcosms under different phosphate regimes (330 uM vs 3-6 uM phosphate). The effect of biological nutrient limitation was examined by DNA microarray studies of rhizobacterial gene expression.
Project description:The goal of this study was to evaluate the molecular mechanisms by which Brachypodium distachyon grown with and without Pseudomonas fluorescens (P. fluorescens) strain SBW25 respond to Fe deprivation. Fe deprivation induced Brachypodium secretion of phytosiderophores and reduced biomass production while inoculation with P. fluorescens resulted in alterations of extracellular metabolite abundances. Results provide insight into the role of iron in interactions between a host plant and root associated bacteria.
Project description:Pseudomonas fluorescens strain SS101 (Pf.SS101) promotes growth of Arabidopsis thaliana, enhances greening and lateral root formation, and induces systemic resistance (ISR) against the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Here, targeted and untargeted approaches were adopted to identify bacterial determinants and underlying mechanisms involved in plant growth promotion and ISR by Pf.SS101. Based on targeted analyses, no evidence was found for volatiles, lipopeptides and siderophores in plant growth promotion by Pf.SS101. Untargeted, genome-wide analyses of 7,488 random transposon mutants of Pf.SS101 led to the identification of 21 mutants defective in both plant growth promotion and ISR. Many of these mutants, however, were auxotrophic and impaired in root colonization. Genetic analysis of three mutants followed by site-directed mutagenesis, genetic complementation and plant bioassays revealed the involvement of the phosphogluconate dehydratase gene edd, the response regulator gene colR and the adenylsulfate reductase gene cysH in both plant growth promotion and ISR. Subsequent comparative plant transcriptomics analyses strongly suggest that modulation of sulfur assimilation, auxin biosynthesis and transport, steroid biosynthesis and carbohydrate metabolism in Arabidopsis are key mechanisms linked to growth promotion and ISR by Pf.SS101. Comparative transcriptome analysis of Arabidopsis treated with Pf. SS101, a growth and ISR promoting rhizobacteria and plants treated with cysH mutant of Pf.SS101 that fails to induce the afformentioned phenotypes
Project description:DNA methylation is an epigenetic modification that differs between plant organs and tissues, but the extent of variation between cell types is not known. Here, we report single-base resolution whole genome DNA methylomes, mRNA transcriptomes, and small RNA transcriptomes for six cell populations covering the major cell types of the Arabidopsis root meristem. We identify widespread cell type specific patterns of DNA methylation, especially in the CHH sequence context. The genome of the columella root cap is the most highly methylated Arabidopsis cell characterized to date. It is hypermethylated within transposable elements, accompanied by increased abundance of transcripts encoding RNA-directed DNA methylation (RdDM) pathway components and 24 nt small RNAs. Absence of the nucleosome remodeler DECREASED DNA METHYLATION 1, required for maintenance of DNA methylation, and low abundance of histone transcripts involved in heterochromatin formation suggests a loss of heterochromatin may occur in the columella, thus allowing access of RdDM factors to the whole genome, and producing excess 24 nt small RNAs in this tissue. Together, these maps provide new insights into the epigenomic diversity that exists between distinct plant somatic cell types. MethylC-seq from six cell populations covering the major cell types of the Arabidopsis root meristem.
Project description:Asymptomatic plants grown in natural soil are colonized by phylogenetically structured communities of microbes known as the microbiota. Individual microbes can activate microbe-associated molecular pattern (MAMP)-triggered immunity (MTI), which limits pathogen proliferation but curtails plant growth, a phenomenon known as the growth-defense trade-off. We report that in mono-associations, 41% (62/151) of taxonomically diverse root bacteria commensals suppress Arabidopsis thaliana root growth inhibition (RGI) triggered by immune-stimulating MAMPs or damage-associated molecular patterns. Amplicon sequencing of bacteria 16S rRNA genes reveal that immune activation alters the profile of synthetic communities (SynComs) comprised of RGI-non-suppressive strains, while the presence of RGI-suppressive strains attenuates this effect. Root colonization by SynComs with different complexities and RGI-suppressive activities alters the expression of 174 core host genes with functions related to root development and nutrient transport. Further, RGI-suppressive SynComs specifically downregulate a subset of immune-related genes. Mutation of one commensal-downregulated transcription factor, MYB15, or pre-colonization with RGI-suppressive SynComs render plants more susceptible to opportunistic Pseudomonas pathogens. Our results suggest that RGI-non-suppressive and suppressive root commensals modulate host susceptibility to pathogens by either eliciting or dampening MTI responses, respectively. This interplay buffers the plant immune system against pathogen perturbation and defense-associated growth inhibition, ultimately leading to commensal-host homeostasis.
Project description:Development of cereal crops with high nitrogen-use efficiency (NUE) is a priority for worldwide agriculture. In addition to conventional plant breeding and genetic engineering, the use of the plant microbiome offers another approach to improve crop NUE. To gain insight into the bacterial communities associated with sorghum lines that differ in NUE, a field experiment was designed comparing 24 diverse sorghum lines under sufficient and deficient nitrogen (N). Amplicon sequencing and untargeted gas chromatography-mass spectrometry (GC-MS) were used to characterize the bacterial communities and the root metabolome associated with sorghum genotypes varying in sensitivity to low N. We demonstrated that N stress and sorghum type (energy, sweet, and grain sorghum) significantly impacted the root-associated bacterial communities and root metabolite composition of sorghum. We found a positive correlation between sorghum NUE and bacterial richness and diversity in the rhizosphere. The greater alpha diversity in high NUE lines was associated with the decreased abundance of a dominant bacterial taxa, Pseudomonas. Multiple strong correlations were detected between root metabolites and rhizosphere bacterial communities in response to low-N stress. This indicates that the shift in the sorghum microbiome due to low-N is associated with the root metabolites of the host plant. Taken together, our findings suggest that host genetic regulation of root metabolites plays a role in defining the root-associated microbiome of sorghum genotypes differing in NUE and tolerance to low-N stress.