Candidate Effector Pst_8713 Impairs the Plant Immunity and Contributes to Virulence of Puccinia striiformis f. sp. tritici

Abstract

<i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>), the causal agent of stripe rust, is an obligate biotrophic pathogen responsible for severe wheat disease epidemics worldwide. <i>Pst</i> and other rust fungi are acknowledged to deliver many effector proteins to the host, but little is known about the effectors' functions. Here, we report a candidate effector Pst_8713 isolated based on the genome data of CY32 and the expression of <i>Pst_8713</i> is highly induced during the early infection stage. The <i>Pst_8713</i> gene shows a low level of intra-species polymorphism. It has a functional N-terminal signal peptide and its product was found in the host cytoplasm and nucleus. Co-infiltrations in <i>Nicotiana benthamiana</i> demonsrated that Pst_8713 was capable of suppressing cell death triggered by mouse pro-apoptotic protein-BAX or <i>Phytophthora infestans</i> PAMP-INF1. Overexpression of Pst_8713 in plants suppressed pattern-triggered immunity (PTI) -associated callose deposition and expression of PTI-associated marker genes and promoted bacterial growth <i>in planta</i>. Effector-triggered immunity (ETI) induced by an avirulent <i>Pst</i> isolate was weakened when we overexpressed Pst_8713 in wheat leaves which accompanied by reduction of reactive oxygen species (ROS) accumulation and hypersensitive response (HR). In addition, the host induced gene silencing (HIGS) experiment showed that knockdown of <i>Pst_8713</i> weakened the virulence of <i>Pst</i> by producing fewer uredinia. These results indicated that candidate effector Pst_8713 is involved in plant defense suppression and contributes to enhancing the <i>Pst</i> virulence.