Characterization of chitinase activity and gene expression in muskmelon seeds

Abstract

AbstractChitinase is often produced in higher plants as a general defence response after wounding or pathogenic attack. Since germinating seeds are exposed to soil pathogens, the activity and expression of chitinase in muskmelon (Cucumis meloL.) seeds was investigated. One acidic and three basic chitinase isoforms were detected, beginning 40 d after anthesis in developing and fully mature seeds. Both acidic and basic chitinase isoforms were found in endosperm tissue during imbibition and after radicle emergence. Basic chitinase isoforms, but not acidic isoforms, were detected in the embryonic axes of imbibed seeds and in seeds before germination, indicating that chitinases are developmentally regulated in specific seed tissues. Two complete cDNAs,Cmchi1andCmchi2, were cloned from germinated muskmelon seeds and are predicted to encode chitinases that show 95% identity to a class III chitinase from cucumber (Cucumis sativusL.) and 61% identity to a class II chitinase from soybean (Glycine maxL.), respectively. Southern blotting indicated thatCmchi2was present only once in the muskmelon genome, whileCmchi1may be present in one or two copies.Cmchi1andCmchi2mRNAs were only detected in radicles of germinating seeds and in roots of mature plants, so additional genes other thanCmchi1andCmchi2must be responsible for the chitinase activity in developing seeds. Salicylic acid and benzothiadiazole stimulated the expression ofCmchi1, but notCmchi2, after radicle emergence. A putative role for chitinase in muskmelon seeds is defence against fungal pathogens.