The Nuclear-Localized RxLR Effector PvAvh74 From Induces Cell Death and Immunity Responses in .

Downy mildew is one of the most serious diseases of grapevine ( spp). The causal agent of grapevine downy mildew, , is an obligate biotrophic oomycete. Although oomycete pathogens such as are known to secrete RxLR effectors to manipulate host immunity, there have been few studies of the associated mechanisms by which these may act. Here, we show that a candidate RxLR effector, PvAvh74, induces cell death in leaves. Using agroinfiltration, we found that nuclear localization, two putative -glycosylation sites, and 427 amino acids of the PvAvh74 carboxyl terminus were necessary for cell-death-inducing activity. Using virus-induced gene silencing (VIGS), we found that PvAvh74-induced cell death in requires EDS1, NDR1, SGT1, RAR1, and HSP90, but not BAK1. The MAPK cascade components MEK2, WIPK, and SIPK were also involved in PvAvh74-induced cell death in . Transient expression of PvAvh74 could suppress colonization of , which suggests that PvAvh74 elicits plant immune responses. Suppression of colonization also was dependent on nuclear localization of PvAvh74. Additionally, PvAvh74-triggered cell death could be suppressed by another effector, PvAvh8, from the same isolate. This work provides a framework to further investigate the interactions of PvAvh74 and other RxLR effectors with host immunity.