Hybrid sterility maintains species identity by restricting gene flow between species. Recently, Yang et al. have elucidated for the first time a molecular mechanism by which hybrid sterility is mediated. They identified three genes that interact in a killer–protector system to regulate sterility in a hybrid of the indica and japonica subspecies of cultivated rice (Oryza sativa L.).
The authors focused on the S5 locus, which has previously been shown to be required for sterility in indica–japonica hybrids. Upon crossing the two subspecies, they found that there was a segregation distortion of the indica (S5-i) and japonica (S5-j) genotypes when crossing the two lines, with the preferential transmission of the indica genotype.