A pepper ( C apsicum annuum L .) metacaspase 9 ( C amc9 ) plays a role in pathogen‐induced cell death in plants

Summary Metacaspases, which belong to the cysteine‐type C 14 protease family, are most structurally similar to mammalian caspases than any other caspase‐like protease in plants. A tmc9 ( A rabidopsis thaliana metacaspase 9) has a unique domain structure, and distinct biochemical characteristics, such as Ca 2+ binding, pH , redox status, S ‐nitrosylation and specific protease inhibitors. However, the biological roles of A tmc9 in plant–pathogen interactions remain largely unknown. In this study, a metacaspase gene present as a single copy in the pepper genome, and sharing 54% amino acid sequence identity with A tmc9, was isolated and named C apsicum annuum metacaspase 9 ( C amc9). C amc9 encodes a 318‐amino‐acid polypeptide with an estimated molecular weight of 34.6  kDa , and shares approximately 40% amino acid sequence identity with known type II metacaspases in plants. Quantitative reverse transcription‐polymerase chain reaction analyses revealed that the expression of C amc9 was induced by infections of X anthomonas campestris pv. vesicatoria race 1 and race 3 and treatment with methyl jasmonate. Suppression of C amc9 expression using virus‐induced gene silencing enhanced disease resistance and suppressed cell death symptom development following infection with virulent bacterial pathogens. By contrast, overexpression of C amc9 by transient or stable transformation enhanced disease susceptibility and pathogen‐induced cell death by regulation of reactive oxygen species production and defence‐related gene expression. These results suggest that C amc9 is a possible member of the metacaspase gene family and plays a role as a positive regulator of pathogen‐induced cell death in the plant kingdom.