Dominant Awn Inhibitor, which encodes an ALOG protein in sorghum, suppresses awn formation in rice

The awn, a needle-like structure that extends from the tip of the lemma in grass species, is believed to play a role in environmental adaptation and fitness. Wild species of cereal crops tend to have longer awns, whereas modern cultivars display a variety of awn lengths and morphologies. Awns in some crops seem to have been eliminated during domestication, and genes controlling awn formation have been reported. Interestingly, a few single dominant factors that eliminate awns are already known; in sorghum (Sorghum bicolor), for example, the dominant awn inhibitor has been known for a century, though its molecular identity remains uncharacterized. In this study, we conducted quantitative trait locus (QTL) analysis and a genome-wide association study of awn-related traits in sorghum. Among the three QTLs controlling awn presence and length, one of them, mapped on chromosome 3, had an extraordinary effect on eliminating awns. We provide a line of evidence demonstrating that this QTL corresponds to Dominant Awn Inhibitor (DAI), encoding an ALOG family protein that potentially acts as a transcription factor. Detailed analysis of the ALOG protein family in cereals revealed that DAI was considered to originate from a gene duplication of its twin paralogue on chromosome 10. Interestingly, heterologous expression of DAI with its own promoter in rice inhibited awn formation in the awned cultivar Kasalath. Our finding that DAI was born by gene duplication provides an interesting example of gain-of-function, which occurs only in sorghum but shares its functionality with rice and sorghum.