Oxalotrophic bacteria protect plants from fungal infection independently of classic plant defense signaling pathways

ROMERO, MATÍAS; VILLARREAL NATALIA; GARRIZ, ANDRÉS; MARTÍNEZ, GUSTAVO ADOLFO; PIECKESTAIN, FERNANDO; MARINA MARIA

Corrientes

Congreso; XXXI Reunión Argentina de Fisiología Vegetal (RAFV); 2017

Oxalic acid plays a key role as a virulence factor for the necrotrophic fungi Botrytis cinerea and Sclerotinia sclerotiorum. Two oxalotrophic strains (OxA and OxB) of the bacterial genus Stenotrophomonas were isolated from the rhizosphere of tomato plants. These strains were able to endophytically colonize Arabidopsis leaves and protected them from damage caused by oxalate application. OxA and OxB did not induce defence-gene expression in Arabidopsis (PR1and PDF1.2) and tomato (PR1and pinII). Both strains induced callose deposition and accumulation of phenolic compounds. Moreover, OxB down-regulated the expression of plant genes involved in cell wall metabolism, suggesting that cell wall degradation is attenuated in leaves colonized by this strain. In addition, OxA and OxB protected Arabidopsis leaves from S. sclerotiorumand B. cinerea infection, although none of these bacteria inhibited growth of the above-mentioned pathogens in vitro. Moreover, in  sid2-2 and coi1Arabidopsis mutants respectively affected in signalling pathways mediated by salicylic acid and jasmonates, both isolates exerted a protective effect against fungal pathogens in a similar way to wild type plants. Results hereby presented suggest that these oxalotrophic bacteria protect plants against oxalate-producing pathogens by degrading oxalic acid and strengthening plant cell walls.