The evolution of sex-independent transmission ratio distortion involving multiple allelic interactions at a single locus in rice

Transmission ratio distortion (TRD) is frequently observed in inter- and intra-specific hybrids of plants, leading to a violation of Mendelian inheritance. Sex-independent TRD (siTRD) was detected in a hybrid between Asian cultivated rice and its wild ancestor. Here we examined how siTRD caused by an allelic interaction at a specific locus arose in Asian rice species. The siTRD is controlled by the S₆ locus via a mechanism in which the S₆ allele acts as a gamete eliminator, and both the male and female gametes possessing the opposite allele (S₆^a) are aborted only in heterozygotes (S₆/S₆^a). Test-cross experiments using near-isogenic lines carrying either the S₆ or S₆^a alleles revealed that Asian rice strains frequently harbor an additional allele (S₆ⁿ) the presence of which, in heterozygotic states (S₆/S₆ⁿ and S₆^a/S₆ⁿ), does not result in siTRD. Fine mapping revealed that the S₆ locus is located near the centromere of chromosome 6. A prominent reduction in the nucleotide diversity of S₆ or S₆^a carriers relative to that of S₆ⁿ carriers was detected in the chromosomal region. These results suggest that the two incompatible alleles (S₆ and S₆^a) arose independently from S₆ⁿ, and established genetically discontinuous relationships between limited constituents of the Asian rice population.

Key Words: Allelic interaction, Hybrid sterility, Rice, Sex-independent TRD

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
phone: 412-268-1812   fax: 412-268-1813   email: genetics-gsa{at}andrew.cmu.edu