CaSGT1 Is Required In PcINF1/CaSRC2-1 Induced Pepper Defense Response By Interacting With CaSRC2-1

Full length of Phytophthora capsici INF1(PcINF1) was previously isolated from a cDNA library of Phytophthora capsici, and it was found to be able to induce hypersensitive reaction (HR) cell death in pepper (Capsicum annuum L.) by interacting with CaSRC2-1, which was accompanied by HR-associated and hormones-dependent marker genes’ expression downregulation, but the underlying mechanism remains uninvestigated.In the present study, we make a further analysis and found that CaSGT1 is involved in the PcINF1/CaSRC2-1-induced immunity:CaSGT1 was found to interact with CaSRC2-1 by yeast-two-hybrid system, and the CaSGT1/CaSRC2-linteraction was further confirmed by bimolecular fluorescence complementation(BiFC) and co-immunoprecipitation(Co-IP). In addition, CaSGT1 was found to be up-regulated by Phytophthora capsici inoculation and synergistically transient overexpression of PcINF1/CaSRC2-1 in pepper plants. CaSGT1-silencing using virus-induced-gene-silencing(VIGS) significantly compromised HR cell death triggered by PcINF1/CaSRC2-1 co-overexpression, and also blocked H2O2 accumulation, downregulated the expression of immunity-associated marker genes. Simultaneous CaSGT1 and CaSRC2-1 silencing by VIGS reduced cell death and the expression of immunity-associated genes to a much lower level compared to that resulting from the individual silencing of each gene alone or the unsilenced control plants. Furthermore, we also found that CaSGT1 and CaSRC2-1 silencing by VIGS can reduce each other in HR cell death induction by transient expression. More importantly, we also found that the CaSGT1/CaSRC2-1 interaction was enhanced by transient overexpression of both PcINF1 transient overexpression and P. capsici inoculation, while CaSGT1 silencing attenuated PcINF1/CaSRC2-1 interaction.Taken together, these results suggest that CaSGT1 is required in immunity triggered by PcINF1/CaSRC2-1 by interacting with CaSRC2-1. Given CaSRC2-1 contains the conserved Ca2+-binding domain, the result of this study provide a molecular link between Ca2+signaling associated CaSGT1-mediated defense signaling.