Pepper (Capsicum annum L.) Metacaspase Homologue Camc9 Functions as a Positive Regulator of Cell Death

Abstract

Cysteine proteases such as caspases play important roles in programmed cell death (PCD) of metazoans. Metacaspases, a family of cysteine proteases are structurally similar to caspases than any other caspase-like proteases in plants. In type2 Arabidopsis metacaspases, Arabidopsis metacaspase 9 (Atmc9) has a shorter linker region between domain p10 and p20 and less than 40% identity compared to type II metacaspases. However, the biological roles of Atmc9 in plant-pathogens interaction remain largely unknown. A Capsicum annuum metacaspase 9 (Camc9) is structurally homologous to Atmc9. I demonstrated that the loss of Camc9 function delayed cell death that was induced by bacterial pathogens. Conversely, a gain of Camc9 function enhanced cell death. Under jasmonate signaling, over-expression of Camc9 accelerated hypersensitive response cell death. These results strongly suggest that Camc9 is a positive regulator in pathogen-induced plant cell death via the JA-mediated singling pathway.