Project description:Small RNAs are the non-coding RNAs known to regulate various biological functions such as stress adaptation, metabolism, virulence as well as pathogenicity across wide range of bacteria, mainly by controlling mRNA stabilization or regulating translation. Identification and functional characterization of sRNAs that has been carried out in various plant growth promoting bacteria have shown to help the bacterial cell cope up with environmental stress. Till now no study has been carried out to uncover these regulatory molecules in diazotrophic alpha-proteobacterium Azospirillum brasilense Sp245. RNA-Seq is a suitable approach for expression-based sRNA identification in bacteria.
Project description:Azospirillum is a plant growth promoting rhizobacteria (PGPR) with ability to produce several phytohormones such as auxins, mainly indole-3-acetic acid (IAA). The positive interaction of Azospirillum with plants has been simplified and explained through the bacterial capacity to produce IAA. Typical changes on root architecture by promoting the number of lateral roots and hair formation, and reducing the primary root length were established in inoculated plants. These changes increase the root surface improving the water and nutrients acquisition, and thus the growth of the whole plant. The mechanisms by which Azospirillum induces such changes fails to be explained only by the bacterial capacity to produce IAA. In this work, we have evaluated the root architecture and gene expression changes occurred in Arabidopsis thaliana inoculated with A. brasilense Az39 and the IAA-deficient mutant (Az39 ipdC-), or treated with exogenous IAA solution to confirm both, the IAA-dependent and IAA-independent Azospirillum´s pathways to promote the root growth. Our results demonstrate the ability of Az39 to modify the primary root development through IAA biosynthesis, while other IAA-independent mechanisms were related to an increase in the lateral roots development and the root hairs number. Jasmonates, ethylene and salicylic acid were increased in the IAA-deficient bacterial treatments, as the ipdC mutant significantly up-regulated transcription of genes enriched of these phytohormones signaling after 7 days. Further, the physical presence of the inactive bacteria (Az39φ) seems to mediate the development of root hairs, a mechanism common to other non-PGPR as E. coli DH5α. Our results suggest that Az39 inoculation induces morphological changes in root architecture through both IAA-dependent and independent mechanism. The IAA biosynthesis by Az39 reduces the primary root length; while the cells contact with the roots increases the root hairs production. Both the synthesis of active IAA and the presence of metabolically active Az39 cells increase the growth and development of lateral roots.
Project description:Azospirillum brasilense is a free-living diazothophic bacterium that associates with important grasses and cereals, promoting plant growth and increasing crop productivity. The nitrogen metabolism in this organism is tightly regulated by the availability of nitrogen and by the Ntr regulatory system. This system comprises the GlnD protein, which is capable of adding uridylyl groups to the PII proteins, GlnB and GlnZ, under limiting nitrogen levels. Under such conditions, the histidine kinase NtrB cannot interact with GlnB and phosphorylate NtrC. When phosphorylated, NtrC is a transcriptional activator of genes involved in metabolism of alternative nitrogen sources. Considering the key role of NtrC in nitrogen metabolism in Azospirillum brasilense, in this work we evaluated the proteomic and metabolomic profiles of the wild type FP2 strain and its mutant ntrC grown under high and low nitrogen. Analysis of the integrated data identifies, novel NtrC targets, including proteins involved in the response against oxidative stressnm (i.e., glutathione S-transferase and hydroperoxide resistance protein,), underlining the importance of NtrC to bacterial survival under oxidative stress conditions.
