A SHORT INTERNODES (SHI) family transcription factor gene regulates awn elongation and pistil morphology in barley

Abstract

The awn, an apical extension from the lemma of the spikelet, plays important roles in seed dispersal, burial, and photosynthesis. Barley typically has long awns, but short-awn variants exist. The short awn 2 (lks2) gene, which produces awns about 50% shorter than normal, is a natural variant that is restricted to Eastern Asia. Positional cloning revealed that Lks2 encodes a SHI-family transcription factor. Allelism tests showed that lks2 is allelic to unbranched style 4 (ubs4) and breviaristatum-d (ari-d), for which the phenotypes are very short awn and sparse stigma hairs. The gene identity was validated by 25 mutant alleles with lesions in the Lks2 gene. Of these, 17 affected either or both conserved regions: the zinc-binding RING-finger motif and the IGGH domain. Lks2 is highly expressed in awns and pistils. Histological observations of longitudinal awn sections showed that the lks2 short-awn phenotype resulted from reduced cell number. Natural variants of lks2 were classified into three types, but all shared a single-nucleotide polymorphism (SNP) that causes a proline-to-leucine change at position 245 in the IGGH domain. All three lks2 natural variants were regarded as weak alleles because their awn and pistil phenotypes are mild compared with those of the 25 mutant alleles. Natural variants of lks2 found in the east of China and the Himalayas had considerably different sequences in the regions flanking the critical SNP, suggesting independent origins. The available results suggest that the lks2 allele might have a selective advantage in the adaptation of barley to high-precipitation areas of Eastern Asia.

An-1 Encodes a Basic Helix-Loop-Helix Protein That Regulates Awn Development, Grain Size, and Grain Number in Rice

“…Recently, Lks2, which regulates awn length in barley, was cloned and natural variation in the conserved domain of Lks2 led to short awns in some varieties. The putative ortholog of Lks2 in rice is Os06g0712600, but no QTL for awn length has been mapped within this region in rice (Yuo et al, 2012). In our study, two QTLs, An-1 and An-2, were mapped on chromosome 4.…”

The MossPhyscomitrella patensReproductive Organ Development Is Highly Organized, Affected by the TwoSHI/STYGenes and by the Level of Active Auxin in theSHI/STYExpression Domain

“…In addition, they are required for the morphogenesis of both vegetative and reproductive organs. SHI/STY members in barley (Hordeum vulgare) have also been shown to be important for gynoecium morphogenesis (Yuo et al, 2012), suggesting that their function in female reproductive organ development may be conserved among angiosperms. We have shown that Arabidopsis SHI/STY family members act as DNA-binding transcriptional activators that control the expression of YUC genes Eklund et al, 2010a).…”

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.…”