Abstract: In order to clarify whether the gene CaSYT1 encoding Synaptotagmin（SYT）protein in pepper may play an important role in pepper’s response to Phytophthora capsici infection. The expression pattern and function of CaSYT1 were preliminarily studied by protein conserved structure prediction，subcellular localization，P. capsici and exogenous hormone treatments，transient expression and virus-induced gene silencing. The results showed that CaSYT1 contained one transmembrane helix domain and two C2 domains，which were located to the plasma membrane. The transcript levels of CaSYT1 were induced by P. capsici infection and exogenous hormone SA，and the CaSYT1 promoter activities were activated and trigger the expression of downstream genes under P. capsici infection and exogenous SA treatment. The transient expression of CaSYT1 can induce the accumulation of H2O2 in pepper leaves and trigger obvious hypersensitive response（HR）-like cell death. CaSYT1 silencing enhanced pepper resistance to P. capsici infection，accompanied by up- regulated expression of resistance-related genes，including CaPR1，NPR1，and CaDEF1，suggesting CaSYT1 plays a negative regulatory role in pepper response to P. capsici infection. CaSYT1 transient expression can trigger H2O2 accumulation and cell death，indicating that CaSYT1 plays a negative regulatory role in pepper response to P. capsici infection in a manner independent of cell death and H2O2 accumulation.

Key words: Capsicum annuum, CaSYT1, Phytophthora capsici, gene identification, signal passage, expression analysis