The DROOPING LEAF and OsETTIN2 genes promote awn development in rice

Abstract

SUMMARYThe 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 Oryza 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 OsETTIN2 (OsETT2) are involved in awn development in the awned indica strain Kasalath. Genetic analyses and RNA-silencing experiments indicate that DL and OsETT2 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. OsETT2 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 OsETT2 in the awn primordium is probably associated with the failure of awn formation in japonica strains.

Loss of function at RAE2 , a previously unidentified EPFL, is required for awnlessness in cultivated Asian rice

“…A similar phenomenon has been reported in Arabidopsis; AtEPFL4 and AtEPFL6 coordinate development of inflorescence architecture (28). In a previous mutant study, DL and OsETT2 were reported to be involved in rice awn development (39). DL is a YABBY gene, essential for forming leaf midribs by promoting cell proliferation, and OsETT2 is an auxinresponsive factor.…”

Fine mapping of a major QTL for awn length in barley using a multiparent mapping population

“…In addition, no direct orthologues of known awn-length related genes were identified within the QTL region. Awn length related genes in rice identified so far include: the zinc finger DROOPING LEAF ( OsDL ); the auxin response factor ETTIN2 ( OsETT2 ); awn - 1 ( an - 1 ) and an - 2 which encode, respectively a basic helix-loop-helix protein and the LONELY GUY LIKE PROTEIN 6 ( OsLOGL6 ), which catalyses the final step of cytokinin synthesis; and LONG AND BARBED AWN1 ( OsLABA1 ), which encodes a cytokinin-activating enzyme (Luo et al 2013; Toriba and Hirano 2014; Gu et al 2015, Hua et al 2015). Selection of the candidate genes was done based on the variant calling and expression analysis of the RNA sequencing.…”

“…Taken together, this MLOC_54434.1 appears to be a promising candidate gene for this major awn length QTL. Noteworthy, two awn length related genes Lks2 and DL also contain a zinc-finger domain (Yuo et al 2012; Toriba and Hirano 2014). However, phylogenetic analysis indicates that there is no strong homology with MLOC_54434.1 and these previously described awn length related genes.…”

LABA1, a Domestication Gene Associated with Long, Barbed Awns in Wild Rice

“…The derived allele, an-1, which confers loss of awns and an increase in grain yield, was selected by humans during rice domestication (Luo et al, 2013). In addition, molecular mechanisms underlying awn traits are recently being addressed (Yuo et al, 2012;Toriba and Hirano, 2014). In this study, we focus on the transition from long, barbed awns to short, barbless awns during rice domestication and elucidate the molecular basis for this critical change.…”