Potato StLecRK-IV.1 negatively regulates late blight resistance by affecting the stability of a positive regulator StTET8

Plant receptor-like kinases (RLKs) regulate many processes in plants. Many RLKs perform significant roles in plant immunity. Lectin receptor-like kinases (LecRLKs) are a large family of RLKs. However, the function of most LecRLKs is poorly understood. In this study, we show that a potato LecRLK, StLecRK-IV.1, is involved in plant immunity against Phytophthora infestans. As a negative regulator of immunity, StLecRK-IV.1 is downregulated by P. infestans and activated by abscisic acid. The transient expression of StLecRK-IV.1 in Nicotiana benthamiana enhanced P. infestans leaf colonization significantly. In contrast, the size of disease lesions caused by P. infestans was reduced by virus-induced gene silencing of the StLecRK-IV.1 ortholog in N. benthamiana, NbLecRK-IV.1, as well as in potato plants with stable RNA interference of StLecRK-IV.1. Tetraspanin-8 (StTET8) was identified to be interacting with StLecRK-IV.1 using a membrane yeast two-hybrid system, which was further verified by co-immunoprecipitation, a luciferase complementation assay, and a bimolecular fluorescence complementation test. StTET8 is a positive immune regulator that restrains P. infestans infection. The co-expression of StLecRK-IV.1 with StTET8 antagonized the positive roles of StTET8 against P. infestans. Moreover, the co-expression of StTET8 with StLecRK-IV.1 affected the stability of StTET8, which was confirmed by a western blot assay and confocal assay. Taken together, our work first reveal that a potato L-type lectin RLK, StLecRK-IV.1, negatively regulates plant immunity by targeting a positive regulator, StTET8, through affecting its stability.