Abstract
Puccinia striiformis f. sp. tritici (Pst), the causal agent of stripe rust, is an obligate biotrophic pathogen responsible for severe wheat disease epidemics worldwide. Pst 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 Pst_8713 is highly induced during the early infection stage. The Pst_8713 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 Nicotiana benthamiana demonsrated that Pst_8713 was capable of suppressing cell death triggered by mouse pro-apoptotic protein-BAX or Phytophthora infestans 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 in planta. Effector-triggered immunity (ETI) induced by an avirulent Pst 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 Pst_8713 weakened the virulence of Pst by producing fewer uredinia. These results indicated that candidate effector Pst_8713 is involved in plant defense suppression and contributes to enhancing the Pst virulence.
Highlights
Plant innate immunity provides a defense against pathogens and attacks from parasites (Jones and Takemoto, 2004)
Yin and Hulbert (2011) reported the use of bacterial type three secretion systems (TTSS) to deliver proteins into wheat cells, which is feasible for studying the functions of Puccinia striiformis f. sp. tritici (Pst) effectors
The expression of Pst_8713 was highly up-regulated in infected wheat leaves compared to the non-germinated urediniospores and germ tubes, and the expression level reached its peak at 18 hpi when Pst haustoria were formed in wheat
Summary
Plant innate immunity provides a defense against pathogens and attacks from parasites (Jones and Takemoto, 2004). PAMPs are recognized by plant transmembrane pattern recognition receptors (PRRs) and trigger PAMP-triggered immunity (PTI) including callose deposition and expression of defense related genes (Chisholm et al, 2006; Jones and Dangl, 2006). Effectors can interfere with PTI and force plants into the layer of immune defense system (Jones and Dangl, 2006). The host-induced gene silencing (HIGS) technique has greatly facilitated research on pathogenicity progressing and has enhanced the study of Pst effectors (Nowara et al, 2010; Yin and Hulbert, 2015). Yin and Hulbert (2011) reported the use of bacterial type three secretion systems (TTSS) to deliver proteins into wheat cells, which is feasible for studying the functions of Pst effectors. Our results showed that Pst_8713 significantly impairs the plant immunity and plays an important role in rust pathogenicity
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