Characterization of Domestication Loci Associated with Awn Development in Rice

Rice (Oryza sativa L.) is a widely studied domesticated model plant. Seed awning is an unfavorable trait during rice harvesting and processing. Hence, loss of awn was one of the target characters selected during domestication. However, the genetic mechanisms underlying awn development in rice are not well understood. In this study, we analyzed and characterized the genes for awn development using a mapping population derived from a cross between the Korean indica cultivar 'Milyang23' and a near-isogenic line NIL4/9 derived from a cross between 'Hwaseong' and Oryza minuta. Two quantitative trait loci (QTLs), qAwn4 and qAwn9, mapped on chromosomes 4 and 9, respectively, increased awn length in an additive manner. Through comparative sequencing analyses of the parental lines, LABA1 was determined as the causal gene underlying qAwn4. qAwn9 was mapped to a 199-kb physical region between markers RM24663 and RM24679. Within this interval, 27 annotated genes were identified, and five genes, including a basic leucine zipper transcription factor 76 (OsbZIP76), were considered as candidate genes for qAwn9 based on their functional annotations and sequence variations. Haplotype analysis using the candidate gene revealed tropical-japonica specific sequence variants in the qAwn9 region, which partly explains the non-detection of qAwn9 in previous studies that used progenies from interspecific crosses. This provides further evidence that OsbZIP76 is possibly a causal gene for qAwn9. The O. minuta qAwn9 allele was identified as a major QTL, providing an important molecular target for understanding the genetic control of awn development in rice. Our results lay the foundation for further cloning of the awn gene underlying qAwn9.