Laboratory of Radiation Genetics and Chemical Mutagenesis, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan
Two plasmid-like DNAs, named B-1 (2.0 kb) and B-2 (1.6 kb), were found in the
mitochondrial genome obtained from a BT line which possessed the male-sterile
cytoplasm of Chinsurah Bore II (Yamaguchi and Kakiuchi 1983). We extracted
mitochondrial DNAs from the calluses of several rice strains showing
cytoplasmic male sterility, Chinsurah boro II, Dian-nong 1A and 1B, and
Zhenshan 97A, and analysed them by agarose gel electrophoresis. For this,
calluses were induced on Murashige and Skoog medium containing 2, 4-D (4 ppm),
since the seeds of the male-sterile strains were limited. Chinsurah boro II has
a male-sterile cytoplasm and fertility-restoring genes, so that it is fertile.
The male-sterile cytoplasms of Dian-nong 1A and Zhen-shan 97A were derived from
different strains of the common wild rice in China. Dian-nong 1B is the
maintainer of Dian-non 1A having the same nuclear background as of 1A and a
normal cytoplasm.
The electrophoresis gave two plasmid-like DNAs in the mitochondrial DNA of Chinsurah Boro II, Dian-nong 1A and Zhen-shan 97A. Molecular weights of these two DNAs were similar to those of B-1 and B-2 reported previously (Yamaguchi and Kakiuchi 1983).
It seems that the mitochondrial DNA of male-sterile cytoplasms contains specifically two plasmid-like DNAs besides the principal genome, and that these small DNAs exist irrespective of the presence or absence of fertility-restoring genes. It remains unknown whether or not these DNAs are integrated into the mitochondrial principal genome. The two specific plasmid-like DNAs are usually found in male-sterile cytoplasms of different origins.
Reference
Yamaguchi, H. and H. Kakiuchi, 1983. Electrophoretic analysis of mitochondrial
DNA from normal and male sterile cytoplasms in rice. Jpn. J. Genet. 58: 607-
611.