CaCBL1 Acts as a Positive Regulator in Pepper Response to .

Bacterial wilt caused by is an important disease of pepper (), an economically important solanaceous vegetable worldwide, in particular, under high temperature (HT) conditions. However, the molecular mechanism underlying pepper immunity against bacterial wilt remains poorly understood. Herein, CaCBL1, a putative calcineurin B-like protein, was functionally characterized in the pepper response to inoculation (RSI) under HT (RSI/HT). was significantly upregulated by RSI at room temperature (RSI/RT), HT, or RSI/HT. CaCBL1-GFP fused protein targeted to whole epidermal cells of when transiently overexpressed. silencing by virus-induced gene silencing significantly enhanced pepper susceptibility to RSI under RT or HT, while its transient overexpression triggered hypersensitive response mimic cell death and upregulation of immunity-associated marker genes, including , , and , the positive regulators in the pepper response to RSI or HT found in our previous studies. In addition, by chromatin immunoprecipitation PCR and electrophoretic mobility shift assay, was found to be directly targeted by CaWRKY40, although not by CaWRKY27 or CaWRKY58, via the W-box-2 within its promoter, and its transcription was found to be downregulated by silencing of while it was enhanced by its transient overexpression. These results suggest that CaCBL1 acts as a positive regulator in pepper immunity against infection, constituting a positive feedback loop with .