Bin WANG, Yu-Nan LI, Wen CHEN and Da-Dong LI
Institute of Genetics, Academia Sinica, Beijing, China
Plasmid-like mitochondrial DNA (mtDNA) associated with cytoplasmic male sterility (CMS) have been reported in some higher plants, e.g., maize, sorghum, sugarbeet, Brassica, Vicia faba, and sunflower. In 1983, Yamaguchi and Kakiuchi first discovered two plasmid-like mtDNAs, B-1 and B-2, associated with CMS in the BT type. We will report other two plasmid-like mtDNAs found in rice.
Fig. 1.Comparison of rice major mtDNA in different sterile types.
1. BT type 2. WA type A. Sterile line 3. Hong Lian type B. Maintainer line 4. Bambis type
Fig. 2. Rice major mtDNA in different lines of BT type. 1. Nong Hu 26. A. Sterile line 2. Qiu Guang. B. Maintainer line 3. Xiu Ling.
Fig. 3. Agarose gel electrophoresis of rice mitochondrial DNA. S: Standard molecular marker Lambda/EcoRI+HindIII A: Sterile line B: Maintainer C: Restorer D: Hybrid (F1)
By 1% agarose gel electrophoresis, we analyzed the MtDNAs from CMS lines of WA, BT, Gambia and Hong Lian types, respectively, which were the four major types of male-sterile cytoplasms used in hybrid rice production in China. In each case, the mtDNAs from male-sterile line, maintainer line, restorer line and F1 hybrids were analyzed simultaneously, and comparisons among them were made.
A 19 kbp mtDNA band was found in the sterile line of BT type. But it was absent in its maintainer line. Originallv, this mtDNA band was named "M". Now it is renamed "pLMR 1" (plasmid-like mtDNA of rice). pLMR 1 was not found in the mtDNAs of WA, Gambia and Hong Lian type cytoplasms (Fig. 1). However, pLMR 1 was found in all of the examined mtDNAs from sterile lines of BT type (Fig. 2).
In all of the examined mtDNAs, some low molecular weight (LMW) DNA bands sized in the range of 1.2-4.2 kbp were found. They were named pLMR 2, pLMR 3, pLMR 4 and pLMR 5, respectively. In different sterile lines, the number of LMW DNA bands varied.
In the case of Nong Hu 26 (BT type), the mtDNA from sterile line was different from that of its maintainer line. The sterile line of Nong Hu 26 contained pLMR 4, but its maintainer line did not (Fig. 3). These plasmid-like mtDNAs were identified. Results showed that they are sensitive to DNase and nuclease 1, but insensitive to RNase. Cloning of pLMR 1 and pLMR 4 is being done.
Yamaguchi, H. and Kakiuchi, 1983. Electrophoretic analysis of mitochondrial DNA from normal and male sterile cytoplasms in rice. Jpn. J. Genet. 58: 607-611.