(go to KOMUGI Home) (go to WIS List) (go to NO.76 Contents)

---

Wheat Information Service
Number 76: 67-70 (1993)


Interorganellar translocation of chloroplast genes into mitochondria

S. Yanagawa and Y. Ogibara

Kihara Institute for Biological Research, Yokohama City University, Nakamura-cho 2-120-3, Yokoharna 232, Japan


Mitochondria genome of angiosperm is known to show some characteristic features such as; 1) plasticity of genome structure, 2) promiscuous DNAs, and 3) RNA editing. In order to analyze the promiscuous DNAs in the mitochondria genome of common wheat, interorganellar translocation of chloroplast genes into mitochondria genome was investigated.

Fourteen cosmid clones which cover the entire part of master circle DNA of common wheat mitochondria (Quetier et al 1985) were amplified, and their DNAs were extracted. Chloroplast and mitochondrial DNAs were also extracted from young seedling of common wheat, Triticum aestivum cv. Chihoku as controls. Those DNAs were digested with Sal I and supplied for Southern hybridization. DNA probes corresponding to 33 chloroplast genes out of 56 protein coding genes, including rRNA genes were prepared with digestion of the appropriate restriction endonucleases and/or PCR amplification after the computer search of rice chloroplast DNA (Hiratsuka et al 1989). Rice chloroplast genes used in the present study are listed in Table1.

Southern hybridization analysis of cosmid DNAs using these DNA probes showed that homologous sequences with 14 out of 33 chloroplast genes were detected in the cosmid clones of mitochondrial DNA. The chloroplast genes whose homologous sequences were found in mitochondrial DNA are listed up in Table 2. It is noteworthy that rbcL gene whose homologous sequence was found in the mitochondria genome of maize (Lonsdale et al 1983) and rice (Moon et al 1988) was not detected in wheat mitochondrial DNA. Physical map of homologous portions in mitochondrial DNA with chloroplast genes is shown in Fig.1. Translocation units were almost corresponded to each chloroplast gene, because no gene clusters of chloroplast DNA were found in wheat mitochondria genome. These lines of evidence suggest that translocation mode of chloroplast genes in wheat group differed from those of rice and maize. Furthermore, it should be emphasized that translocation hot spots in the mitochondrial DNA were found: Fragment L₁ contains five kinds of homomogous sequence, and T harbors three homologous sequences. On the other hand, fragments C₂ to AC carry no homologous sequences with chloroplast genes (Fig.1).DNA sequencing around the translocated region is required to estimate translocation mechanism(s).


Acknowledgments

This work was supported in part by a Grant-in-Aid for Scientific Research (No. 03640542) from the Ministry of Education, Science and Culture, Japan and a grant from Sapporo Bioscience Foundation, Japan.


References

Hiratsuka J, Shimada H, Whittier R, Ishibashi T, Sakamoto M, Mori M, Kondo C, Honji Y, Sun CR, Meng BY, Li YQ, Kanno A, Nishizawa Y and Hirai A (1989) The complete sequence of rice (Oryza sativa) chloroplast genome: Intermolecular recombination between distinct tRNA genes accounts for a major plast DNA inversion during the evolution of the cereals. Mol Gen Genet 217: 185-194.

Lonsdale DM, Hodge TP, Howe CJ and Stern DB (1983) Maize mitochondrial DNA contains a sequence homologous to the ribulose-1,5-bisphosphate carboxylase large subunit gene of chloroplast DNA. Cell 34: 1007-1014.

Moon E, Kao T-H and Wu R (1988) Rice mitochondrial genome contains a rearranged chloroplast gene cluster. Mol Gene Genet 213: 247-253.

Quetier F, Lejeune B, Delorme S and Falconet D (1985) Molecular organization and expression of the mitochondrial genome of higher plants. In: Encyclopedia of Plant Physiology 18. Ed. Doce R and Days DA. pp. 25-36. Springer-Verlag.

(go to KOMUGI Home) (go to WIS List) (go to NO.76 Contents)