Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki 710-0046, Japan.
J Exp Bot. 2012 Sep;63(14):5223-32. doi: 10.1093/jxb/ers182. Epub 2012 Jul 12.
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.
芒，小穗颖片的顶端延伸物，在种子传播、埋藏和光合作用中起着重要作用。大麦通常具有长芒，但也存在短芒变体。短芒 2（lks2）基因产生的芒大约比正常的短 50%，是一种自然变体，仅存在于东亚。定位克隆表明，Lks2 编码一个 SHI 家族转录因子。等位基因测试表明，lks2 与不分枝的风格 4（ubs4）和短芒-稀疏柱头毛（ari-d）等位，这些表型是非常短的芒和稀疏的柱头毛。通过 25 个具有 Lks2 基因损伤的突变等位基因验证了基因同一性。其中，17 个影响或同时影响两个保守区域：锌结合 RING-指结构域和 IGGH 结构域。Lks2 在芒和雌蕊中高度表达。对纵向芒切片的组织学观察表明，lks2 短芒表型是由于细胞数量减少所致。lks2 的自然变体被分为三种类型，但都共享一个单核苷酸多态性（SNP），导致 IGGH 结构域第 245 位的脯氨酸到亮氨酸变化。所有三种 lks2 自然变体都被认为是弱等位基因，因为它们的芒和雌蕊表型与 25 个突变等位基因相比较为温和。在中国东部和喜马拉雅山脉发现的 lks2 自然变体在关键 SNP 侧翼区域的序列有很大差异，表明它们是独立起源的。现有的结果表明，在大麦适应东亚高降水地区的过程中，lks2 等位基因可能具有选择优势。
