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Summary: The oomycete pathogen Hyaloperonospora arabidopsidis delivers diverse effector proteins into host plant cells to suppress the plant's innate immunity. In this study, we investigate the mechanism of action of a conserved RxLR effector, HaRxLL470, in suppressing plant immunity.Genomic, molecular and biochemical analyses were performed to investigate the function of HaRxLL470 and the mechanism of the interaction between HaRxLL470 and the target host protein during H. arabidopsidis infection.We report that HaRxLL470 enhances plant susceptibility to H. arabidopsidis isolate Noco2 by interacting with the host photomorphogenesis regulator protein HY5. Our results demonstrate that HY5 is not only an important component in the regulation of light signalling, but also positively regulates host plant immunity against H. arabidopsidis by transcriptional activation of defense‐related genes. We show that the interaction between HaRxLL470 and HY5 compromises the function of HY5 as a transcription factor by attenuating its DNA‐binding activity.The present study demonstrates that HY5 positively regulates host plant defense against H. arabidopsidis whereas HaRxLL470, a conserved RxLR effector across oomycete pathogens, enhances pathogenicity by interacting with HY5 and suppressing transcriptional activation of defense‐related genes. [ABSTRACT FROM AUTHOR]

Plasmopara viticola, the causal organism of grapevine downy mildew, secretes a vast array of effectors to manipulate host immunity. Previously, several cell death‐inducing PvRXLR effectors have been identified, but their functions and host targets are poorly understood. Here, we investigated the role of PvRXLR111, a cell death‐inducing RXLR effector, in manipulating plant immunity. When coexpressed with other PvRXLR effectors, PvRXLR111‐induced cell death was prevented. Transient expression of PvRXLR111 in Nicotiana benthamiana suppressed bacterial flagellin peptide flg22‐elicited immune responses and enhanced Phytophthora capsici infection. PvRXLR111 induction in Arabidopsis increased susceptibility to Hyaloperonospora arabidopsidis. PvRXLR111 expression in Pseudomonas syringae promoted bacterial colonization. By immunoprecipitation‐mass spectrometry analysis, yeast two‐hybrid, pull‐down, and bimolecular fluorescence complementation assays, it was shown that PvRXLR111 interacted with Vitis vinifera putative WRKY transcription factor 40 (VvWRKY40), which increased VvWRKY40 stability. Transient expression of VvWRKY40 in N. benthamiana inhibited flg22‐induced reactive oxygen species burst and enhanced P. capsici infection and silencing NbWRKY40 attenuated P. capsici colonization. These results suggest VvWRKY40 functions as a negative regulator in plant immunity and that PvRXLR111 suppresses host immunity by stabilizing VvWRKY40. [ABSTRACT FROM AUTHOR]

Based on previous cloning of VpRPW8‐e, we obtained a 1,126 bp VpRPW8‐e promoter sequence in this study. A large number of TATA‐boxes, CAAT‐boxes, and other cis‐acting elements were predicted including light‐responsive elements, hormone‐responsive elements, stress‐responsive elements, and growth‐ and development‐associated elements within the promoter sequence. To further investigate the function of this promoter, we examined its activity in response to biotic and abiotic stress. The VpRPW8‐e promoter was strongly activated by Plasmopara viticola infection, and activation also occurred when the orientation of the promoter was reversed, although to a lesser extent. Deletion analysis showed that the −1,126 to −475 bp region of VpRPW8‐e promoter had high activity. A promoter fragment 5′ deleted to −475 bp (P−475) was activated in response to heat and cold stress, and even more strongly in response to Phytophthora capsici and salicylic acid (SA). Furthermore, Transgenic Nicotiana benthamiana were generated, VpRPW8‐e driven by P−475 enhanced resistance to Ph. capsici in N. benthamiana. Based on these results, the −475 bp region was deduced to be an indispensable part of the VpRPW8‐e promoter. VpRPW8‐e promoter is involved in pathogen‐ and stress‐inducible expression. [ABSTRACT FROM AUTHOR]