Fertility of CMS wheat is restored by two Rf loci located on a recombined acrocentric chromosome

Summary

The high potential for an acrocentric chromosome originated from a complex reorganization of chromosomes 1H ^chS and 6H ^chS from Hordeum chilense in the development of hybrid wheat technology.

Abstract

Cytoplasmic male sterility (CMS) results from incompatibility between nuclear and cytoplasmic genomes, and is characterized by the inability to produce viable pollen. The restoration of male fertility generally involves the introgression of nuclear genes, termed restorers of fertility ( Rf). CMS has been widely used for hybrid seed production in many crops but not in wheat, partly owing to the complex genetics of fertility restoration. In this study, an acrocentric chromosome that restores pollen fertility of CMS wheat in Hordeum chilense cytoplasm (msH1 system) is studied. The results show that this chromosome, of H. chilense origin and named H ^chac, originated from a complex reorganization of the short arm of chromosomes 1H ^ch (1H ^chS) and 6H ^ch (6H ^chS). Diversity arrays technology (DArT) markers and cytological analysis indicate that H ^chac is a kind of `zebra-like′ chromosome composed of chromosome 1H ^chS and alternate fragments of interstitial and distal regions of chromosome 6H ^chS. PCR-based markers together with FISH, GISH, and meiotic pairing analysis support this result. A restorer of fertility gene, named Rf _6H ^ch _S , has been identified on the short arm of chromosome 6H ^chS. Moreover, restoration by the addition of chromosome 1H ^chS has been observed at a very low frequency and under certain environmental conditions. Therefore, the results indicate the presence of two Rf genes on the acrocentric chromosome: Rf _6H ^ch _S and Rf _1H ^ch _S , the restoration potential of Rf _6H ^ch _S being greater. The stable and high restoration of pollen fertility in the msH1 system is therefore the result of the interaction between these two restorer genes.