Gluconacetobacter diazotrophicus triggers ISR involving SA and JA/Et defense-related pathways to respond against Ralstonia solanacearum in Arabidopsis and optimizes the cellular redox state maintaining reduced FITNESS levels.

Abstract

Abstract Background and Aims: Pest biocontrol mechanisms are beneficial effects provided by plant-PGPBEs association and remain to be elucidated. Therefore, we evaluated the possible signaling pathways involved in Arabidopsis plant defense inoculated with beneficial endophytic bacterium Gluconacetobacter diazotrophicus and phytopathogen Ralstonia pseudosolanacearum. Methods: Anatomical, physiological and genetic responses during GD-ISR (activated by inoculation with G. diazotrophicus Pal5), RP-IR (activated by inoculation with R. pseudosolanacearum GMI1000) and GDRP-ISR (both bacteria) were analyzed. Col-0, sid2 mutant and transgenic NahG were used for these studies and defense-related genes from SA and JA/Et pathways were investigated. Results: sid2 plants showed reduced colonization by G. diazotrophicus with respect to Col-0 plants and increases in xylem tissue in stems and roots of inoculated sid228 dpi plants were less significant than those observed in Col-0. Pr1 transcripts were augmented in inoculated Col-0 plants, while pdf 1.2 levels remained unaltered, indicating a strong role of the SA pathway during GD-ISR. Transcripts myc2 levels were elevated during GD-ISR and upon R. pseudosolanacearum infection levels of pdf 1.2 increased significantly, indicating that G. diazotrophicus primes the defense response against R. pseudosolanacearum. During RP-IR, pdf1.2 levels increased indicating activation of the JA pathway by R. pseudosolanacearum. G. diazotrophicusmanaged to maintain low levels of fitness during GD-ISR and GDRP-ISR, leading to optimization of the stress responses network. Conclusions: G. diazotrophicus utilizes the SA pathway for effective colonization and GD-ISR activation, and primes the JA defense pathway during GD-ISR to protect Arabidopsis against the R. pseudosolanacearum during GDRP-ISR.