Chloroplast DNA polymorphism in different types of cytoplasmic male sterile rice

The lengths of open reading frame (ORF)100 and ORF29-TrnC(GCA), the intronic sequence of rps16 and the transcribed spacer of TrnT(UGU)-TrnL(UAA) in chloroplast from different lines of cytoplasmic male sterility (CMS) rice were studied using indica types, japonica types and common wild rice as controls. The results show that the lengths of ORF100 and ORF29-TrnC(GCA) in CMS lines are similar to those of typical indica. The sequences of the rps16 intron and the TrnT(UGU)-TrnL(UAA) spacer in sporophyte sterile types (wild-abortive type, Yinshui type and K type) are almost the same, and they also share a molecular marker of GTTGAG at nucleotide positions 220-225 in the rps16 intron. Therefore, it is speculated that the source of these three types is the same. In contrast, a gametophyte sterile type, Yuetai A does not contain such a GTTGAG sequence in the rps16 intron and has a unique G at position 595, which may works as a molecular marker distinguishing the sporophyte sterile type from the gametophyte sterile type. Based on the observation that CMS rice has much lower cytoplasmic polymorphism than indica, japonica and wild rice, it is concluded that CMS rice lack cytoplasm diversity. Therefore, it is important to introduce new sources of cytoplasm into hybrid rice.