The DROOPING LEAF and O s ETTIN 2 genes promote awn development in rice

Summary The awn is a long needle‐like appendage that, in some grass species, is formed on the lemma that encloses floral organs together with the palea. In rice, most wild species and most strains of O ryza sativa ssp. indica generate an awn, whereas most strains of O . sativa ssp. japonica do not. In japonica , the long‐awn characteristic appears to have been lost during domestication and breeding programs. Here, we found that the genes DROOPING LEAF ( DL ) and O s ETTIN 2 ( O s ETT 2 ) are involved in awn development in the awned indica strain K asalath. Genetic analyses and RNA ‐silencing experiments indicate that DL and O s ETT 2 act independently in awn formation, and that either gene alone is not sufficient for awn development. Scanning electron microscopy revealed that the top region of the lemma (a putative awn primordium) is larger in an awned floret than in an awnless floret. O s ETT 2 is expressed in the awn primordium in the awned indica floret, but not in the awnless japonica floret except in the provascular bundle. DL is expressed underneath the primordium at similar levels in both indica and japonica florets, suggesting non‐cell‐autonomous action. We hypothesize that loss of expression of O s ETT 2 in the awn primordium is probably associated with the failure of awn formation in japonica strains.