Project description:Characterization of the transcriptomic responses of grafted tomato seedlings leaves after the root inoculations with the two beneficial microorganisms Paraburkholderia graminis and Azospirillum brasiliensis. Paraburkholderia graminis treatment led to a higher number of differentially expressed genes than Azospirillum brasiliensis, with a higher amount of up-regulated than down-regulated genes for both treatments. These DEGs were manly involved in response to oxidative stress, response to biotic and abiotic stress, water transport, regulation of transcription and hormones. Only few DEGs were shared among the two treatments, including genes involved in flowering time and in tolerance against abiotic stresses.
Project description:Paraburkholderia phymatum is a beta-proteobacterium, which lives in the soil and is able to enter nitrogen-fixing symbiosis with different legumes. The biological nitrogen fixation (BNF) process is of great ecological and agronomic importance. We previously showed that the expression of the key P. phymatum BNF enzyme – the nitrogenase –is regulated by the sigma factor σ54 (or RpoN) inside root nodules. This study focused on identifying the σ54 regulon of P. phymatum grown in nitrogen limited conditions using RNA-Sequencing. Among the genes significantly down-regulated in absence of σ54 we found those coding for a C4-dicarboxylate transport system (Bphy_0225-27), a flagellar biosynthesis cluster (Bphy_2926-64) and one of the two type 6 secretion system (T6SS-b) present in P. phymatum genome (Bphy_5978-97). Indeed, the σ54 mutant was unable to grow on C4 dicarboxylates (fumarate, malate and succinate) as the sole carbon source and was less motile compared to the wild-type strain. Both defects were complemented by adding rpoN in trans. Additionally, using reporter fusions we confirmed that T6SS-b expression is regulated by σ54. Finally, a σ54 mutant was less competitive than its parental strain against P. diazotrophica, suggesting a role of σ54 in controlling interbacterial competition.
