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

Koide, YI, M.; Sawamura, N.; Nishimoto, D.; Matsubara, K.; Onishi, K.; Kanazawa, A.; Sano, Y.,  Genetics,  180:409-420. 2008.

Transmission ratio distortion (TRD) is frequently observed in inter-and intraspecific 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 is controlled by the S-6 locus via a mechanism in which the S-6 allele acts as a gamete eliminator, and both the male and female gametes possessing the opposite allele (S-6(a)) are aborted only in heterozygotes (S-6/S-6(a)). Fine mapping revealed that the S-6 locus is located neaar the centromere of chromosome 6. Tescross experiments using near-isogenic lines (NILs) carrying either the S-6 or S-6(a) alleles revealed that Asian rice strains frequently harbor an additional allele (S-6(n)) the presence of which, in heterozygotic states (S-6/S-6(n) and S-6(a)/S-6(n)), does not result in siTRD. A prominent reduction in the nucleotide diversity of S-6 or S-6(a) carries relative to that of S-6(n) carries was detected in the chromosomal region. These results suggest that the two incompatible alleles (S-6/S-6(a)) arose independently from S-6(n) and established genetically discontinuous relationships between limited constituents of the Asian rice population.