Impaired sterol ester synthesis alters the response of <i>Arabidopsis thaliana</i> to <i>Phytophthora infestans</i>

<jats:title>Summary</jats:title><jats:p>Non‐host resistance of <jats:italic>Arabidopsis thaliana</jats:italic> against <jats:italic>Phytophthora infestans</jats:italic>, the causal agent of late blight disease of potato, depends on efficient extracellular pre‐ and post‐invasive resistance responses. Pre‐invasive resistance against <jats:italic>P. infestans</jats:italic> requires the myrosinase <jats:styled-content style="fixed-case">PEN</jats:styled-content>2. To identify additional genes involved in non‐host resistance to <jats:italic>P. infestans</jats:italic>, a genetic screen was performed by re‐mutagenesis of <jats:italic>pen2</jats:italic> plants. Fourteen independent mutants were isolated that displayed an <jats:italic>enhanced response to Phytophthora</jats:italic> (<jats:italic>erp</jats:italic>) phenotype. Upon inoculation with <jats:italic>P. infestans</jats:italic>, two mutants, <jats:italic>pen2‐1 erp1‐3</jats:italic> and <jats:italic>pen2‐1 erp1‐4</jats:italic>, showed an enhanced rate of mesophyll cell death and produced excessive callose deposits in the mesophyll cell layer. <jats:italic><jats:styled-content style="fixed-case">ERP</jats:styled-content>1</jats:italic> encodes a phospholipid:sterol acyltransferase (<jats:styled-content style="fixed-case">PSAT</jats:styled-content>1) that catalyzes the formation of sterol esters. Consistent with this, the tested T‐<jats:styled-content style="fixed-case">DNA</jats:styled-content> insertion lines of <jats:italic><jats:styled-content style="fixed-case">PSAT</jats:styled-content>1</jats:italic> are phenocopies of <jats:italic>erp1</jats:italic> plants. Sterol ester levels are highly reduced in all <jats:italic>erp1/psat1</jats:italic> mutants, whereas sterol glycoside levels are increased twofold. Excessive callose deposition occurred independently of <jats:styled-content style="fixed-case">PMR</jats:styled-content>4/<jats:styled-content style="fixed-case">GSL</jats:styled-content>5 activity, a known pathogen‐inducible callose synthase. A similar formation of aberrant callose deposits was triggered by the inoculation of <jats:italic>erp1</jats:italic> <jats:italic>psat1</jats:italic> plants with powdery mildew. These results suggest a role for sterol conjugates in cell non‐autonomous defense responses against invasive filamentous pathogens.</jats:p>