Plasmopara viticolaRxLR effector PvAvh77 triggers cell death and governs immunity responses in grapevine

Abstract

Grapevine downy mildew, caused by the oomycete Plasmopara viticola, is one of the most considerable production challenges for the grape and wine industries. P. viticola injects a plethora of effectors into host cells to disrupt immune processes, but the mechanisms by which these effectors act at the molecular level have not been well characterized. Herein, we show that a candidate P. viticola Avirulence Homolog (Avh) RxLR effector gene, designated PvAvh77, was strongly up-regulated during the initial stages of P. viticola infection in Vitis vinifera. Further experiments demonstrated that PvAvh77 could trigger nonspecific cell death when expressed in the wild grapevine Vitis riparia and in tobacco (Nicotiana benthamiana and Nicotiana tabacum). We also found that a truncated form of PvAvh77, designated PvAvh77-M2, was more active in inducing cell death in N. benthamiana and V. riparia than full-length PvAvh77. Furthermore, PvAvh77-induced cell death required BAK1/SOBIR1, NDR1, SGT1, HSP90, and RAR1, but not EDS1 or MAPK pathway-related genes. Ectopic expression of PvAvh77 in Vitis vinifera cv. Thompson Seedless leaves neutralized host immunity and enhanced colonization by P. viticola, and the immune-inhibiting activity of PvAvh77 on susceptible Eurasian grapevine depended on its nuclear localization. Agrobacterium-mediated transient expression of PvAvh77 in N. benthamiana leaves also interfered with the immune response triggered by flg22. Using a yeast signal sequence trap approach, we showed that the signal peptide of PvAvh77 is functional in yeast. Moreover, PvAvh77 with a signal peptide stimulated plant immunity responses in the apoplast. Notably, application of exogenous purified PvAvh77-M2 effectively initiated defense responses in grapevines, as evidenced by increased accumulation of salicylic acid (SA) and H2O2, and reduced infection of inoculated P. viticola. In summary, we identified a novel effector, PvAvh77, from P. viticola, which has the potential to serve as a plant immunity inducer.

Plasmopara viticola effector PvCRN11 induces disease resistance to downy mildew in grapevine

“…Our previous study identified that PvAvh77‐M2 is a deletion mutation of P. viticola RxLR effector PvAvh77, whose purified protein is able to elicit immune responses in the apoplast (Fu et al., 2023). To investigate whether the purified protein of PvCRN11 can also initiate plant immunity in the apoplast, we purified the PvCRN11 protein using a prokaryotic expression system.…”

“…Here, similarly to other pathogenic oomycetes, the causative agent of grapevine downy mildew pathogen, P. viticola , produces a repertoire of effectors that are essential for its virulence and pathogenicity (Lan et al., 2019; Lei et al., 2019; Liu, Chen, Ma, et al., 2021; Liu, Chen, Yin, et al., 2021; Ma, Chen, et al., 2021; Xiang et al., 2022; Yin et al., 2022). Although the P. viticola effector PvAvh77 stimulates immune responses in plant apoplast, transient expression of it intracellularly also suppresses plant immunity and promotes pathogen infection (Fu et al., 2023). However, cases have also been reported in which P. viticola effectors can stimulate plant immunity and promote disease resistance in plants.…”

“…In vitro grown plantlets of V. riparia accession ‘Beaumont’ and V. vinifera cv. ‘Thompson Seedless’ were propagated on half‐strength Murashige and Skoog (MS) medium containing 3% sucrose, 0.7% agar and 0.15% activated carbon, and grown under regulated conditions in a climate chamber (Fu et al., 2023). Arabidopsis thaliana , N. benthamiana and ‘Thompson Seedless’ potted plants were grown in a greenhouse (16 h light photoperiod, 25°C, 68% relative humidity).…”

“…In order to expose the spongy mesophyll imaging, the leaves were torn with tweezers to peel off the epidermis at the lower part of the leaves (Levy et al, 2007). GFP and mCherry excitation wavelength and fluorescence capture wavelength settings refer to Fu et al (2023). The images were imported and processed using LAX-AF-Lite_3.3.0 image analysis software.…”

“…The His-tagged plasmid pCold-TF-PvCRN11 Opt was transformed into the E. coli strains BL21 (DE3). The His-PvCRN11 Opt recombinant protein was induced and purified according to the method described by Fu et al (2023). The trigger factor (TF) region in His-PvCRN11 Opt recombinant protein was removed by thrombin for plant immune induction activity analysis.…”