Plant defensin expression triggered by fungal pathogen invasion depends on EDR1 protein kinase and ORA59 transcription factor in <i>Arabidopsis thaliana</i>

<i>Arabidopsis thaliana</i> exhibits durable ‘non-host’ resistance against the hemibiotrophic fungal pathogen <i>Colletotrichum tropicale</i> that infects mulberry plants. <i>Arabidopsis</i> non-host resistance comprises two layers of defense: preinvasive and postinvasive resistance. The EDR1 protein kinase contributes to <i>Arabidopsis</i> preinvasive resistance against <i>C. tropicale</i> by inducing the expression of plant defensin (<i>PDF</i>) genes. Here we report that the expressions of multiple <i>PDF</i> genes were strongly induced in <i>Arabidopsis</i> upon invasion by <i>C. tropicale</i>. Invasion by a necrotrophic pathogen, <i>Alternaria brassicicola</i>, also induced <i>PDF</i> expression. Importantly, <i>PDF</i> expression triggered upon invasion by both pathogens was inhibited in <i>edr1</i> mutants, indicating the requirement of EDR1 for <i>PDF</i> expression in postinvasive resistance by <i>Arabidopsis</i>. Analysis of <i>ora59</i> mutants also revealed that this gene is critical for induced <i>PDF</i> expression following pathogen invasion. Furthermore, inoculation assays of <i>A. brassicicola</i> indicated that <i>ORA59</i> is involved in postinvasive resistance against the pathogen, suggesting invasion-triggered <i>PDF</i> expression contributes to postinvasive resistance in <i>Arabidopsis.</i>