National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
Plant J. 2013 Oct;76(1):36-46. doi: 10.1111/tpj.12268. Epub 2013 Jul 25.
The alteration of photoperiod sensitivity has let breeders diversify flowering time in Oryza sativa (rice) and develop cultivars adjusted to a range of growing season periods. Map-based cloning revealed that the rice flowering-time quantitative trait locus (QTL) Heading date 16 (Hd16) encodes a casein kinase-I protein. One non-synonymous substitution in Hd16 resulted in decreased photoperiod sensitivity in rice, and this substitution occurred naturally in an old rice cultivar. By using near-isogenic lines with functional or deficient alleles of several rice flowering-time genes, we observed significant digenetic interactions between Hd16 and four other flowering-time genes (Ghd7, Hd1, DTH8 and Hd2). In a near-isogenic line with the weak-photoperiod-sensitivity allele of Hd16, transcription levels of Ehd1, Hd3a, and RFT1 increased under long-day conditions, and transcription levels of Hd3a and RFT1 decreased under short-day conditions. Expression analysis under continuous light and dark conditions showed that Hd16 was not likely to be associated with circadian clock regulation. Biochemical characterization indicated that the functional Hd16 recombinant protein specifically phosphorylated Ghd7. These results demonstrate that Hd16 acts as an inhibitor in the rice flowering pathway by enhancing the photoperiod response as a result of the phosphorylation of Ghd7.
光周期敏感性的改变使培育者能够在水稻（Oryza sativa）中多样化开花时间，并开发出适应一系列生长季节的品种。基于图谱的克隆表明，水稻开花时间数量性状位点（QTL）Heading date 16（Hd16）编码一种酪蛋白激酶-I 蛋白。Hd16 中的一个非同义替换导致水稻对光周期敏感性降低，并且这种替换在一个古老的水稻品种中自然发生。通过使用具有几种水稻开花时间基因的功能或缺失等位基因的近等基因系，我们观察到 Hd16 与其他四个开花时间基因（Ghd7、Hd1、DTH8 和 Hd2）之间存在显著的双基因相互作用。在具有 Hd16 弱光周期敏感性等位基因的近等基因系中，Ehd1、Hd3a 和 RFT1 的转录水平在长日照条件下增加，而 Hd3a 和 RFT1 的转录水平在短日照条件下降低。在连续光照和黑暗条件下的表达分析表明，Hd16 不太可能与生物钟调节有关。生化特性分析表明，功能正常的 Hd16 重组蛋白特异性地磷酸化 Ghd7。这些结果表明，Hd16 通过增强对 Ghd7 的磷酸化反应作为光周期响应的抑制剂，在水稻开花途径中起作用。
