Chitosan inhibits septin‐mediated plant infection by the rice blast fungus Magnaporthe oryzae in a protein kinase C and Nox1 NADPH oxidase‐dependent manner

Abstract

<jats:title>Summary</jats:title><jats:p> <jats:list list-type="bullet">

<jats:list-item><jats:p>Chitosan is a partially deacetylated linear polysaccharide composed of β‐1,4‐linked units of <jats:sc>d</jats:sc>‐glucosamine and N‐acetyl glucosamine. As well as a structural component of fungal cell walls, chitosan is a potent antifungal agent. However, the mode of action of chitosan is poorly understood.</jats:p></jats:list-item>

<jats:list-item><jats:p>Here, we report that chitosan is effective for control of rice blast disease. Chitosan application impairs growth of the blast fungus <jats:italic>Magnaporthe oryzae</jats:italic> and has a pronounced effect on appressorium‐mediated plant infection. Chitosan inhibits septin‐mediated F‐actin remodelling at the appressorium pore, thereby preventing repolarization of the infection cell.</jats:p></jats:list-item>

<jats:list-item><jats:p>Chitosan causes plasma membrane permeabilization of <jats:italic>M. oryzae</jats:italic> and affects NADPH oxidase‐dependent synthesis of reactive oxygen species, essential for septin ring formation and fungal pathogenicity. We further show that toxicity of chitosan to <jats:italic>M. oryzae</jats:italic> requires the protein kinase C‐dependent cell wall integrity pathway, the Mps1 mitogen‐activated protein kinase and the Nox1 NADPH oxidase. A conditionally lethal, analogue (PP1)‐sensitive mutant of Pkc1 is partially remediated for growth in the presence of chitosan, while <jats:italic>∆nox1</jats:italic> mutants increase their glucan : chitin cell wall ratio, rendering them resistant to chitosan.</jats:p></jats:list-item>

<jats:list-item><jats:p>Taken together, our data show that chitosan is a potent fungicide which requires the cell integrity pathway, disrupts plasma membrane function and inhibits septin‐mediated plant infection.</jats:p></jats:list-item> </jats:list> </jats:p>