Cytoplasmic male sterility in rice
Cytoplasmic male sterility (CMS) is used for hybrid seed production including rice. In CMS, a male sterility gene in mitochondria causes failure of development of a male reproductive organ or pollen, and male sterility is restored by a nuclear gene that encodes a protein localized in mitochondria and suppresses a corresponding male sterility gene. We have been studying to understand mechanisms of CMS by identifying a male sterility gene, a restorer of fertility gene and their interaction. We also have been trying to develop novel CMS lines of rice.
CMS of rice is often observed in a sibling obtained by successive back crossing between distantly related cultivars or strains, and various different types of CMS exist in rice. This means that a different restorer of fertility (Rf) gene suppresses its corresponding CMS gene with a different mechanism. For example, in BT-type CMS, Rf1, which encodes mitochondria-localized pentatricopeptide repeat (PPR) protein, suppresses mitochondrial CMS gene orf79 by an RNA-processing mechanism. CW-type CMS shows a very unique mechanism. Rf17 gene is expressed at a normal level in a nucleus of a fertile plant. However, in combination with a corresponding CMS gene in mitochondria, the expression level of Rf17 is up-regulated, which results in male sterility. An Rf17 allele whose expression is not up-regulated even in the presence of the CMS gene plays a role for an Rf gene.
We have been generating various types of CMS plants in rice , and analysing their Rf genes, CMS genes and their interaction using molecular genetics and genetic engineering techniques.
A flower of wild rice and pollens of CMS lines of cultivated rice. Mitochondria determine pollen fates. T65: Taichung 65 (fertile), WA, BT, CW: CMS lines.
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