Jasmonate-dependent expression of a galactinol synthase gene is involved in priming of systemic fungal resistance in Arabidopsis thaliana

Previously, root colonization by the rhizobacterium, Pseudomonas chlororaphis O6, was shown to induce expression of galactinol synthase conferring systemic resistance against a fungal pathogen in cucumber leaves. Here, the Arabidopsis – Botrytis cinerea system is introduced to better understand signal transduction of galactinol and (or) raffinose family oligosaccharides (RFO) during O6-mediated induced systemic resistance (ISR). Among the 10 Arabidopsis galactinol synthase genes, only AtGolS1 was specifically induced upon infection with the fungal pathogen B. cinerea. AtGolS1 was primed by O6 colonization against the pathogen in Arabidopsis leaves. Arabidopsis T-DNA insertion mutants at the AtGolS1 gene site compromised O6-mediated ISR against the pathogen, thereby suggesting that AtGolS1 plays an important role in ISR. O6 colonization increased AtGolS1 transcription as well as ISR in several Arabidopsis signaling mutants, but not in the jar1-1 and coi1 mutant lines. Exogenous jasmonate treatment induced transcription of AtGolS1 in wild-type Col-0 plants, but salicylic acid and 1-aminocyclopropane-1-carboxylate did not. These studies on signaling mutants and target gene expression indicate that expression of AtGolS1 in response to O6 colonization is mediated through the jasmonate-dependent pathway, stimulating ISR in Arabidopsis against B. cinerea infection.