Distribution, Function And Digital Expression Analysis Of Plant Metacaspase

Hypersensitive reaction is an important process in plant disease resistance. Similar to apoptosis in animals, it is actually a process of programmed cell death (PCD). It has been known that caspases (cysteine-dependent aspartate-specific proteases) play a central role in animal apoptotic pathways. Update, no orthologous proteins of caspases are found in plants; but a group of proteins with similar structures, termed metacaspases, are found. Two types (typel and II) of metacaspases could be distinguished based on the similarity of sequences and structures. Some PCD processes in plants depend on metacaspases, others do not. Research on structure and function of metacaspases has been conducted. The biological functions of metacaspases and their roles in PCD pathways in plants remain to be explored. The distribution of metacaspase genes in plants was analyzed by using bioinformatics in this study. This article analyzed the structure and function of metacaspase genes and proteins in Arabidopsis thaliana and Oryza sativa, and mined the function related genes of these metacaspases through gene chip data analysis. The related genes could be involved in programmed cell death or other processes of cell response to stimulations.Analyses showed that there was a positive correlation between the gene number of metacaspase and genome size of plants with known genomic sequences. Higher plants have more metacaspase genes than lower ones. The gene number of metacaspase between dicotyledon and monocotyledon had not significant difference. There are evidences to suggest that some metacaspase genes had been duplicated in Arabidopsis thaliana and Oryza sativa, which provides possibilities for functional differentiation of metacaspase. The analysis results of amino acid sequences of metacaspases, showed that the p20subdomain, in which the presumed conservative catalytic amino acid histidine and cysteine were located, was more conservative than p10, which suggested the functional differences between the two subdomains. The predicted tertiary structure of metacaspase is similar to that of caspase and paracaspase. and the structures of these proteins are presumably originated from the common ancestry. The analysis results of differential expression of metacaspase genes in Arabidopsis thaliana hinted that these genes responsed to environmental stimulating factors in different degree, which could be the consequence of functional differences among these genes. AtMCl, AtMC2, AtMC3. AtMC4, AtMC8participated in the responding process more frequently than AtMC5, AtMC6, AtMC7, AtMC9. Meanwhile, there was no overlap among the intersections of different metacaspase-related genes under divers experimental conditions, which suggested that these metacaspases had different functions and in dissimilar functional module. Most protein products of the metacaspase related genes are zymoproteins. The location and function of the zymoproteins revealed that endomembrane system, mitochondria, chloroplast and cytoskeleton all responsed to stimulating factors. The responding process included many steps, such as signals transduction pathways mediated by protein kinases, generation and dynamic changes of reactive oxygen species and nitric oxide, processing, modification and hydrolysis of proteins, etc. These steps involved a great deal of enzymes including protein kinase, proteolytic enzyme, redox enzyme, transferase and so on. The metacaspase related genes not only participated in PCD, but also in other cell processes responding to physical, chemical and biotic factors. Homologous proteins of some metacaspase-related genes are present in mammals and involved in apoptosis or immune response. This means that the biological processes in which the above proteins participate are conservative between animals and plants.Though some microarray data of Oryza sativa were found, no significantly differential expression of metacaspase genes in Oryza sativa was detected according to the same analytical method and yardstick. Up to now, there are no reports on the functions of metacaspase genes in Oiyza sativa. It’s possible that the functions of metacaspase genes are quite different among various plant species.