Project description:Root exudates contain specialised metabolites that affect the plant’s root microbiome. How host-specific microbes cope with these bioactive compounds, and how this ability shapes root microbiomes, remains largely unknown. We investigated how maize root bacteria metabolise benzoxazinoids, the main specialised metabolites of maize. Diverse and abundant bacteria metabolised the major compound in the maize rhizosphere MBOA and formed AMPO. AMPO forming bacteria are enriched in the rhizosphere of benzoxazinoid-producing maize and can use MBOA as carbon source. We identified a novel gene cluster associated with AMPO formation in microbacteria. The first gene in this cluster, bxdA encodes a lactonase that converts MBOA to AMPO in vitro. A deletion mutant of the homologous bxdA genes in the genus Sphingobium, does not form AMPO nor is it able to use MBOA as a carbon source. BxdA was identified in different genera of maize root bacteria. Here we show that plant-specialised metabolites select for metabolisation-competent root bacteria. BxdA represents a novel benzoxazinoid metabolisation gene whose carriers successfully colonize the maize rhizosphere and thereby shape the plant’s chemical environmental footprint
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:To identify the mechanism of how the microbiota induces lateral root development independently of auxin signalling, we performed a transcriptional analysis using roots of wild type plants and lateral root mutants arf7 arf19, nph4-1, lbd16-1, and gnom184, in mono-association with a selection of 16 bacteria able to restore the lateral root formation in the mutants used.
Project description:The secretion of metabolites by plant roots is a key determinant of microbial growth and colonisation. We have used Pisum sativum and its natural symbiont Rhizobium leguminosarum (it can form N2 fixing nodules on pea roots) to study the natural metabolites secreted by roots. To do this root secretion was harvested from pea plants grown under sterile conditions. This root exudate was then concentrated and used as a sole carbon and nitrogen source for growth of the bacteria in the laboratory. These bacteria were harvested in mid-exponential growth and RNA extracted for microarray analysis. As control cultures the bacteria were grown on 30 mM pyruvate as a carbon source and 10 mM ammonium chloride as a nitrogen source and RNA extracted. Two colour microarrays were performed using root exudate cultures versus pyruvate ammonia grown cultures. This was done in biological triplicate.
Project description:H. seropedicae is a diazotrophic and endophytic bacterium that associates with economically important grasses promoting plant growth and increasing productivity. To identify genes related to bacterial ability to colonize and promote plant growth wheat seedlings growing hydroponically in Hoaglandâs medium were inoculated with H. seropedicae the bacteria and incubated for 3 days. mRNA from the bacteria present in the root surface and in the plant medium were purified, depleted from rRNA and used for RNA-seq profiling. RT-qPCR analyses were conducted to confirm regulation of selected genes. Comparison of RNA profile of bacteria attached to the root and planktonic revealed an extensive metabolic adaptation to the epiphytic life style.