Genomewide survey and characterization of metacaspase gene family in rice (Oryza sativa)

Metacaspases (MCs), which are cysteine-dependent proteases found in plants, fungi, and protozoa, may be involved in programmed cell death processes, being distant relatives of metazoan caspases. In this study, we analysed the structures, phylogenetic relationship, genome localizations, expression patterns and domestic selections of eight MC genes identified in rice (OsMC). Alignment analysis of the corresponding protein sequences suggested OsMC proteins can be classified into two subtypes. The expression profiles of eight OsMC genes were analysed in 27 tissues covering the whole life cycle of rice. There are four OsMC genes uniquely expressed in mature tissues, indicating that these genes might play certain roles in senescence. Under abiotic and biotic stresses, four OsMC genes were expressed with treatments of one or more of Magnaporthe oryzae (M. oryzae) infected, pest damaged, cold stress and drought stress, indicating they might be involved in plant defense. In addition, gene trees and genetic diversity (π) were performed to measure whether candidate genes were selected during rice domestication. The results suggested that all the type I genes could not be domestication genes. However, two of five type II OsMC genes showed strong evidence for selective sweep, suggesting that these genes might be involved in cultivated rice domestication. These results provide a foundation for future functional genomic studies of this family in rice.