Thiol peroxidase CaTPX1 of pepper enhances resistance against Phytophthora capsici by stabilizing CaCDC48

Abstract Identification of key defense-related genes in pepper ( Capsicum annuum L.) against Phytophthora capsici is critical for developing effective disease-resistant breeding strategies. In this study, a cDNA virus-induced gene silencing (VIGS) library in Nicotiana benthamiana was screened, leading to the identification of a thiol peroxidase ( TPX1 ) as a positive regulator of plant immunity against P. capsici . Silencing of the TPX1 homolog in N. benthamiana , pepper, and tomato resulted in decreased resistance, while overexpression of TPX1 homologs in pepper and tomato significantly enhanced resistance to P. capsici . To explore whether TPX1 's function in disease resistance depends on its perception of endogenous H 2 O 2 , the peroxidatic/catalytic cysteine ( CaTPX1 C51S ) was mutated to interrupt the oxidation signaling. The results showed that CaTPX1 C51S lost its ability to positively regulate immunity. To investigate the disease resistance mechanism of CaTPX1 , immunoprecipitation-mass spectrometry (IP-MS) was performed, identifying a cell division cycle 48 (CDC48) protein as an interacting partner of CaTPX1. Co-immunoprecipitation (Co-IP) and luciferase complementation imaging (LCI) assays confirmed the interaction between CaCDC48 and CaTPX1, with the CaTPX1 C51S mutant exhibiting significantly reduced binding affinity for CaCDC48. Further analysis revealed that CaCDC48 is stabilized by CaTPX1, but not by CaTPX1 C51S , indicating that CaTPX1 interacts with CaCDC48 via Cys51, potentially facilitating the transmission of the H 2 O 2 signal to CaCDC48. In addition, CaCDC48 was found to positively regulate pepper defense against P. capsici . In conclusion, our findings suggest that thiol peroxidase CaTPX1 targets and stabilizes CaCDC48 to enhance plant immunity against P. capsici .