Chitosan inhibits septin-mediated plant infection by the rice blast fungus Magnaporthe oryzae in a Protein Kinase C and Nox1 NADPH oxidase-dependent manner

O_LIChitosan is a partially deacetylated linear polysaccharide composed of {beta}-1,4-linked units of D-glucosamine and N-acetyl glucosamine. As well as acting as a structural component of fungal cell walls, chitosan can be applied as a potent antifungal agent. However, the mode-of-action of chitosan in fungal pathogens is poorly understood. C_LIO_LIHere, we report that chitosan is effective for control of rice blast disease. Chitosan application impairs growth of the blast fungus Magnaporthe oryzae and has a pronounced effect on appressorium-mediated plant infection. Chitosan inhibits septin-mediated F-actin re-modelling at the appressorium pore, thereby preventing re-polarisation of the infection cell and rice leaf cuticle penetration. C_LIO_LIWe found that chitosan causes plasma membrane permeabilization of M. oryzae and affects NADPH oxidase-dependent synthesis of reactive oxygen species, essential for septin ring formation and fungal pathogenicity. Our data further show that the toxicity of chitosan to M. oryzae requires the protein kinase C-dependent cell wall integrity pathway and the Nox1 NADPH oxidase. A conditionally lethal, analogue (PP1)-sensitive mutant of Pkc1 is partially remediated for growth in the presence of chitosan and PP1, while {Delta}nox1 mutants increase their glucan/chitin cell wall ratio, rendering them resistant to chitosan. C_LIO_LITaken together, our data show that chitosan is a potent fungicide for control of the rice blast fungus which involves the cell wall integrity pathway, disrupts plasma membrane and inhibits septin-mediated plant infection. C_LI