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>拟南芥（Arabidopsis thaliana）对侵染桑树的半活体营养真菌病原菌热带炭疽菌（Colletotrichum tropicale）表现出持久的非寄主抗性（non-host resistance）。拟南芥的非寄主抗性包含两层防御机制：侵入前抗性与侵入后抗性。EDR1蛋白激酶（EDR1 protein kinase）可通过诱导植物防御素（PDF）基因的表达，参与拟南芥对热带炭疽菌的侵入前抗性。本研究发现，热带炭疽菌侵入拟南芥后，多个PDF基因的表达均被显著诱导。死体营养病原菌芸薹链格孢（Alternaria brassicicola）的侵入同样可诱导PDF基因的表达。值得注意的是，两种病原菌侵入后触发的PDF基因表达均在edr1突变体中受到抑制，这表明EDR1是拟南芥侵入后抗性中PDF基因表达所必需的调控因子。对ora59突变体的分析还显示，ORA59基因对于病原菌侵入后诱导的PDF基因表达至关重要。此外，芸薹链格孢接种实验表明，ORA59参与了对该病原菌的侵入后抗性，这提示侵入触发的PDF基因表达有助于拟南芥的侵入后抗性。