Study On Mitochondrial Respiratory Chain Of Zidao Type Cytoplasmic Male Sterility Rice (Oryza Sativa L.)

Cytoplasmic male sterility (CMS) is a maternally inherited phenotype in plants, which can lead to pollen sterility in plants. CMS is of great importance to rice breeding, as hybrid seeds can be produced by CMS inbred lines rather than manual emasculation. In recent years, the cytoplasm of Yunnan purple rice was used to derive a new type of CMS line named CMS-ZA (ZidaoA) (patent No. ZL 99 1 20003.9). It has been speculated that CMS is linked to mitochondrial respiratory chain (MRC) dysfunction, leading to insufficient ATP generation to meet the demands of pollen development. In the paper, two major works have been done to investigate the mitochondrial respiratory chain of the rice CMS line, its fertile maintainer line and the hybrid F1, which includes:1. Using the sterile line and maintainer line of Yunnan Purple Rice as materials, we have constructed the BAC libraries of their mitochondrial genome. Each library consisted of 2304 clones and the insert size range from 10-20kb. The libraries were screened by PCR analysis using oligonucleotide primers specific for the desired gene (atp6, atp9, cob, cox2). The PCR results showed that the libraries can be used for the mitochondrial genome research and the PCR method is suitable for screening the BAC liabraries.2. Although the vegetative tissues of CMS plants can develop normally, the CMS-related genes are expressed in all organs of sterile plants. In rice CMS lines, ATPases involved in the mitochondrial respiratory chain (MRC) are believed to be dysfunctional. In the present study, we evaluated the MRC ATPase and NADH dehydrogenase (NADH DHase) activities of three different rice lines (a CMS line, a fertile line, and a hybrid line) using in-gel catalytic assays. Our results show that the sterile line has intact ATPase activity, while NADH DHase activity is severely decreased. Using etiolated seedlings and green seedlings from the CMS-ZA sterile and fertile lines, we investigated the effects of NADH DHase deficiency (in sterile lines) on mitochondrial respiration and photorespirationTo investigate NADH dehydrogenase deficiency in mitochondrial respiration and photorespiration, we measured NADH DHase activity in seedlings from the ZidaoA CMS sterile line and the fertile line. We note that the NADH DHase deficiency of the sterile line was enhanced 2-fold in green seedlings. Our results suggest that an optional pathway of interactions between mitochondrial respiration and photorespiration causes rice CMS.3. The absence of ATPase deficiency is partly explained by the presence of the homologous orf79 gene detected in the CMS-ZA sterile line and its corresponding fertile line. We found that chloroplasts may contribute to the NADH DHase deficiency in the mitochondria of CMS rice. These results will help to elucidate the molecular mechanism by which MRC dysfunction leads to CMS in this novel CMS rice line.