Plant Protection by Free Cutin Monomers in Two Cereal Pathosystems

Abstract

The barley and rice fungal pathogens, Erysiphe graminis and Magnaporthe grisea, respectively, secrete cutinase enzyme(s)[1,2]. Cutinases may facilitate adhesion of fungal spores or penetration by softening plant cuticles and release, as final products, plant cutin monomers. Cutin monomers are recognized by a number of fungal pathogens and lead to cutinase-gene activation [e.g. 3,4]. We tested the hypothesis that free cutin monomers are recognized by plant cells and therefore act as endogenous inducers of acquired resistance. Topical spray application of synthetic cutin monomers or of a cutin hydrolysate from apple fruit partially protected barley against E.graminis and rice against M.grisea, the plants being challenge inoculated 1 to 3 days after the application. No fungicidal activity of cutin monomers in vitro against M.grisea or on leaf surfaces against E.graminis could be detected. The analysis of host gene expression includes extracellular PR proteins, lipoxygenase activity, Northern analysis of peroxidase, and 2D patterns of in vitro translation products of barley and rice mRNA. Our results are compatible with a model that includes cutin monomers as inducers of acquired resistance in cereals although a number of typical plant defence genes are not activated by the cutin monomers tested.