P-096 - Root colonization by Pseudomonas kribbensis XP1-6 induces transcriptomic changes promoting tomato thermotolerance

Pseudomonas kribbensis XP1-6 is a plant growth-promoting rhizobacterium isolated from the tomato rhizosphere. Although it can promote growth and enhance thermotolerance in tomato, the molecular mechanisms underlying P. kribbensis XP1-6-mediated tomato responses remain unclear. In this study, we first investigated the role of flagellin in root colonization of P. kribbensis XP1-6 using ΔfliC, the flagellin-deficient mutant. The results showed that ΔfliC colonizes root with significantly lower efficiency, and reduced root fresh weight was observed in tomato plants inoculated with ΔfliC at 28 day post inoculation (dpi), indicating the critical role of flagella in root colonization and plant-growth promoting activity of P. kribbensis XP1-6. Among the 75 differentially expressed genes revealed by transcriptomic analysis at one dpi, the auxin efflux facilitator gene SlPIN10 was upregulated, while the ethylene biosynthesis-related gene SlACCS was downregulated. Physiological assays supported transcriptomic findings, showing enhanced root development and reduced ethylene production at the early colonization stage. Furthermore, the expressions of MAPK3 and HSP101, significant genes involved in tomato thermotolerance, were modulated by P. kribbensis XP1-6 under heat stress. These findings indicate that P. kribbensis XP1-6 colonization rapidly modulates tomato root transcriptomes, promoting growth and priming thermotolerance with an emphasis on flagella in early colonization processes.