Interaction between polygalacturonase-inhibiting protein and jasmonic acid during defense activation in tomato against Botrytis cinerea

Oligogalacturonic acids (OGAs) generated from in vitro interaction between fungal polygalacturonase (PG) and bean PG-inhibiting protein (PGIP) were shown to activate phytoalexin biosynthesis in soybean. Based on this observation, it was hypothesized that PGIP-dependent generation of OGAs activates plant defence responses in vivo. We tested the hypothesis that PGIP activates jasmonic acid-dependent responses to pathogens. For this purpose, a population of tomato plants segregating for a mutation in the jasmonate receptor CORONATINE INSENSITIVE1 (coi1) and for overexpression of pear PGIP (pPGIP) was challenged with Botrytis cinerea. The coi1 mutant was hypersensitive to B. cinerea, but overexpression of pPGIP in the coi1 mutant background reduced pathogen susceptibility, suggesting that these two genes independently alter defence responses. In addition, pPGIP overexpression suppressed pathogen induction of salicylic acid in the coi1 mutant and activated expression of acidic beta-1,3-glucanase independently of the coi1 mutation. However, expression of proteinase inhibitor II (PIN II) in pPGIP over-expressing tomato plants was dependent on COI1. Effects of pPGIP overexpression on defence are therefore complex and only in the case of PIN II pPGIP acts through COI1.