Molecular Characterization of Mitochondrial Genomes of Rice Lines Containing Wild Abortive (WA) Male Sterile and Fertile Cytoplasms

Indian rice breeders have developed hybrid rice using primarily the wild abortive (WA) type cytoplasm for the male sterile parent. In this communication, we report our studies on the molecular characterization of the mitochondrial genomes of male sterile lines possessing this cytoplasm as also the respective maintainer, restorer and restored lines using 16 mitochondrial gene probes. The results show polymorphism in the location of several genes and expression of one of the genes, namely atf 156. Polymorphism in five genes namely coxl, cob, atp6, rrn18 and orf156 differentiates the sterile cytoplasm from the fertile ones while the RFLPs in coxlll and rps14 can differentiate maintainers and restores from each other. The WA cytoplasm is very different from the Chinsurah boro II cytoplasm as is evident from the transcription patterns of afp6. Of the genes studied, only orfl56, which encodes a membrane bound 156 amino acid long polypeptide showed differences in the transcript pattern between the male sterile and fertile cytoplasms. However, it is not clear whether this gene is associated with the CMS trait in WA type of cytoplasm. These studies show the utility of mitochondrial RFLPs to distinguish different cytoplasms existing in the rice lines.