Domain Unknown Function DUF1668-Containing Genes in Multiple Lineages Are Responsible for F Pollen Sterility in Rice.

Postzygotic reproductive isolation maintains species integrity and uniformity and contributes to speciation by restricting the free gene flow between divergent species. In this study we identify causal genes of two Mendelian factors and on rice chromosome 2 inducing F pollen sterility in hybrids between japonica-type cultivar Taichung 65 (T65) and a wild relative of rice species . The causal gene of in T65 encodes a protein containing DUF1668 and gametophytically expressed in the anthers, designated . The allele , allelic to , possesses three non-synonymous substitutions and a 2-bp deletion, leading to a frameshifted translation at the S22B C-terminal region. Transcription level of and/or did not solely determine the fertility of pollen grains by genotypes at . Western blotting of S22B found that one major band with approximately 46 kDa appeared only at the mature stage and was reduced on semi-sterile heterozygotes at , implying that the 46 kDa band may associated in hybrid sterility. In addition, causal genes of in T65 were found to be and encoding DUF1668-containing protein. The allele of a wild rice species Ng at , designated , is a loss-of-function allele probably due to large deletion of the gene lacking DUF1668 domain and evolved from the different lineage of . Phylogenetic analysis of DUF1668 suggested that many gene duplications occurred before the divergence of current crops in Poaceae, and loss-of-function mutations of DUF1668-containing genes represent the candidate causal genetic events contributing to hybrid incompatibilities. The duplicated DUF1668-domain gene may provide genetic potential to induce hybrid incompatibility by consequent mutations after divergence.