A Broadly Distributed Rhizobacterium, <i>Roseateles chitinivorans</i> P500, Promotes Growth and Systemic Resistance via Jasmonic Acid-Dependent Oxylipin Signaling in Grasses

Harnessing root-associated microbiomes to promote beneficial microbial compositions could offer a sustainable strategy to increase crop resilience. Major challenges impeding this strategy are the lack of understanding of which native members of the microbiome benefit the host and the molecular signaling events underlying these benefits. In this study, we isolated a strain of <i>Roseateles chitinivorans</i>, RcP500, corresponding to the most abundant bacterial taxon in the switchgrass root microbiome. Inoculation of roots with RcP500 promoted growth and induced systemic resistance (ISR) to Bipolaris leaf spot of switchgrass and closely related <i>Panicum hallii</i>. <i>R</i>. <i>chitinivorans</i> is also highly abundant in the rhizosphere and root microbiomes of maize and rice and enhanced the growth of these two plant species. Furthermore, RcP500 elicited ISR in maize against anthracnose leaf blight and southern corn leaf blight. Bioassays and root metabolite profiling in maize wild-type and jasmonic acid (JA)-deficient <i>opr7opr8</i> mutant plants revealed the requirement of JA-dependent processes in RcP500-elicited synthesis of the JA precursor, 12-OPDA (<i>cis</i>-(+)-12-oxo-phytodienoic acid), and an α-ketol, 9,10-KODA (9-hydroxy-10-oxo-12(<i>Z</i>)-octadecadienoic acid), two oxylipins previously implicated in ISR signaling. Xylem sap transfusion of RcP500-colonized plants to naïve receiver plants corroborated the role of JA in promoting these signaling intermediates. Whereas root JA synthesis was downregulated upon RcP500 colonization, gibberellic acid was induced, suggesting a potential mechanism behind the simultaneous growth promotion and ISR triggered by this bacterium. Overall, this study identified a novel rhizobacterium with a broad host range that promotes growth and systemic resistance across multiple plant species in a JA-dependent, ketol-driven manner. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.