Toriba Taiyo, Hirano Hiro-Yuki
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-8657, Japan.
Plant J. 2014 Feb;77(4):616-26. doi: 10.1111/tpj.12411.
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 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.
芒是一种长针状附属物，在一些禾本科物种中，它形成于内稃上，内稃与外稃一起包裹着花器官。在水稻中，大多数野生种和大多数籼稻品种都会产生芒，而大多数粳稻品种则不会。在粳稻中，长芒特征似乎在驯化和育种过程中丢失了。在这里，我们发现下垂叶（DL）基因和水稻ETTIN2（OsETT2）基因参与了有芒籼稻品种Kasalath的芒发育。遗传分析和RNA沉默实验表明，DL和OsETT2在芒的形成过程中独立起作用，且单独一个基因不足以促进芒的发育。扫描电子显微镜显示，有芒小花的内稃顶部区域（假定的芒原基）比无芒小花的大。OsETT2在有芒籼稻小花的芒原基中表达，但在无芒粳稻小花中除了在原形成层束外不表达。DL在籼稻和粳稻小花的原基下方以相似水平表达，表明其作用是非细胞自主性的。我们推测，OsETT2在芒原基中表达缺失可能与粳稻品种芒形成失败有关。
