Genetic characterization and fine mapping of <i>S25</i>, a hybrid male sterility gene, on rice chromosome 12

Abstract

Hybrid male sterility genes are important factors in creating postzygotic reproductive isolation barriers in plants. One such gene, S25, is known to cause severe transmission ratio distortion in inter-subspecific progeny of cultivated rice Oryza sativa ssp. indica and japonica. To further characterize the S25 gene, we fine-mapped and genetically characterized the S25 gene using near-isogenic lines with reciprocal genetic backgrounds. We mapped the S25 locus within the 0.67-1.02 Mb region on rice chromosome 12. Further genetic analyses revealed that S25 substantially reduced male fertility in the japonica background, but not in the indica background. In first-generation hybrid progeny, S25 had a milder effect than it had in the japonica background. These results suggest that the expression of S25 is epistatically regulated by at least one partially dominant gene present in the indica genome. This finding supports our previous studies showing that hybrid male sterility due to pollen killer genes results from epistatic interaction with other genes that are hidden in the genetic background.

Two complementary genes in a presence-absence variation contribute to indica-japonica reproductive isolation in rice

“…Taking 70–80% as the cut-off region between semi-sterility and fertility, the population segregated for semi-sterility (<70%): fertility (>80%) at the ratio of 1:1 (χ 2 = 0.13 < χ 2 0.05,1 = 3.84), demonstrating monogenic inheritance for the trait. Our results indicated the substituted segment on chromosome 12 contained a gene locus, designated Se as in previous studies 41 , 42 , controlling HMS between T65 and E9, which was closely linked with RM19 and RM453 and appeared to be allelic to several previously identified HMS QTLs 34 , 43 – 47 .

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“…The utilization of strong heterosis in indica-japonica hybrids is one of the most promising future directions in rice breeding 24 , 38 – 40 , therefore, understanding indica-japonica reproductive isolation is important to unlock their breeding potential. Se/pf12 is a major locus conferring hybrid male sterility in indica-japonica hybrids, which was identified by a large number of studies using different populations 34 , 41 – 47 . Artificial disruption of pf12A gene at Se/pf12 locus successfully converts this hybrid sterility locus into a neutral allele 34 .…”