Identification of Natural Resistance Mediated by Recognition of Phytophthora infestans Effector Gene Avr3aEM in Potato

Abstract

Late blight is considered the most renowned devastating potato disease worldwide. Resistance gene (<i>R</i>)-based resistance to late blight is the most effective method to inhibit infection by the causal agent <i>Phytophthora infestans</i>. However, the limited availability of resistant potato varieties and the rapid loss of <i>R</i> resistance, caused by <i>P. infestans</i> virulence variability, make disease control rely on fungicide application. We employed an <i>Agrobacterium tumefaciens</i>-mediated transient gene expression assay and effector biology approach to understand late blight resistance of Chinese varieties that showed years of promising field performance. We are particularly interested in <i>PiAvr3a^EM</i> , the most common virulent allele of <i>PiAvr3a^KI</i> that triggers a <i>R3a</i>-mediated hypersensitive response (HR) and late blight resistance. Through our significantly improved <i>A. tumefaciens</i>-mediated transient gene expression assay in potato using cultured seedlings, we characterized two dominant potato varieties, Qingshu9 and Longshu7, in China by transient expression of <i>P. infestans</i> effector genes. Transient expression of 10 known avirulence genes showed that <i>PiAvr4</i> and <i>PiAvr8 (PiAvrsmira2)</i> could induce HR in Qingshu9, and <i>PiAvrvnt1.1</i> in Longshu7, respectively. Our study also indicated that <i>PiAvr3a^EM</i> is recognized by these two potato varieties, and is likely involved in their significant field performance of late blight resistance. The identification of natural resistance mediated by <i>PiAvr3a^EM</i> recognition in Qingshu9 and Longshu7 will facilitate breeding for improved potato resistance against <i>P. infestans</i>.