THB1, a putative transmembrane protein that causes hybrid breakdown in rice

Abstract

Hybrid breakdown is a post-zygotic reproductive isolation that hinders genetic exchange between species or populations in both animals and plants. Two complementary recessive genes, temperature sensitive hybrid breakdown1 ( thb1 ) and thb2 , cause hybrid breakdown in rice ( Oryza sativa ). The present study delimited the THB1 locus to a 9.1-kb sequence, containing a single gene encoding a putative transmembrane protein with unknown functions. Haplotype analysis of THB1 in the two core collections of 119 accessions revealed that these accessions were divided into 22 haplotypes. A test cross with thb2 carrier showed that haplotype2 (H2) was assigned to thb1 and was restricted to temperate japonica . A nonsynonymous nucleotide polymorphism (SNP) specific to H2 was identified as a causal mutation in thb1 . A test cross with thb1 carrier indicated that six accessions, including temperate japonica , tropical japonica , and indica , carried thb2 . These results suggest that thb1 has recently evolved in temperate japonica , whereas thb2 arose in an ancient japonica and introgressed into the present three subgroups. Furthermore, we developed a derived cleaved amplified polymorphic sequence (dCAPS) marker to detect causal SNP in THB1 . Our findings provide new insights into reproductive isolation and may benefit rice breeding.