- • A sex-independent transmission ratio distortion (siTRD) system detected in the interspecific cross in rice was analyzed in order to understand its significance in reproductive barriers. The S1 gene, derived from African rice Oryza glaberrima, induced preferential abortion of both male and female gametes possessing its allelic alternative (), from Asian rice O. sativa, only in the heterozygote.
- • The siTRD was characterized by resolving it into mTRD and fTRD occurring through male and female gametes, respectively, cytological analysis of gametophyte development, and mapping of the S1 locus using near-isogenic lines. The allelic distribution of the S1 locus in Asian and African rice species complexes was also analyzed.
- • The siTRD system involved at least two components affecting male and female gametogeneses, respectively, including a modifier(s) that enhances fTRD. The chromosomal location of the major component causing the mTRD was delimited within an approx. 40 kb region. The S1 locus induced hybrid sterility in any pairwise combination between Asian and African rice species complexes.
- • The allelic state of the S1 locus has diverged between Asian and African rice species complexes, suggesting that the TRD system has a significant role in the reproductive barriers in rice.