LAUSR

Plant-growth-promoting rhizobacteria (PGPR) refer to bacteria that colonize the rhizosphere and contribute to plant growth or stress tolerance. To further understand the molecular mechanism of symbiosis of plants-PGPRs, we performed a high-throughput single colony screening from rhizosphere, and uncovered a bacterium (named promoting lateral root, PLR) that significantly promotes Arabidopsis lateral root formation. By 16S rDNA sequencing, PLR was identified as a novel sub-species of Serratia marcescens. RNA-seq analysis of Arabidopsis integrated with phenotypic verification of auxin signaling mutants demonstrated that the promotion effect of PLR on lateral root formation is dependent on auxin signaling. Furthermore, PLR enhanced the tryptophan-dependent IAA synthesis by inducing multiple auxin synthesis genes in Arabidopsis. Genome-wide sequencing of PLR integrated with the identification of IAA and its precursors in PLR exudates showed that tryptophan treatment significantly enhanced the ability of PLR to produce IAA and its precursors IPA and IAM. Interestingly, PLR induced multiple nutrient (N, P, K, S) transporter genes in an auxin-independent manner. In summary, this study provides evidence to show how PLR enhances plant growth through finely tuning auxin biosynthesis and signaling in Arabidopsis, implying a potential application of PLR in crop yield improvement through accelerating root development.