Ikeda-Kawakatsu Kyoko, Yasuno Naoko, Oikawa Tetsuo, Iida Shigeru, Nagato Yasuo, Maekawa Masahiko, Kyozuka Junko
Research Institute for Bioresources, Okayama University, Kurashiki, Okayama 710-0046, Japan.
Plant Physiol. 2009 Jun;150(2):736-47. doi: 10.1104/pp.109.136739. Epub 2009 Apr 22.
Two types of branches, rachis branches (i.e. nonfloral) and spikelets (i.e. floral), are produced during rice (Oryza sativa) inflorescence development. We previously reported that the ABERRANT PANICLE ORGANIZATION1 (APO1) gene, encoding an F-box-containing protein orthologous to Arabidopsis (Arabidopsis thaliana) UNUSUAL FLORAL ORGANS, suppresses precocious conversion of rachis branch meristems to spikelets to ensure generation of certain number of spikelets. Here, we identified four dominant mutants producing an increased number of spikelets and found that they are gain-of-function alleles of APO1. The APO1 expression levels are elevated in all four mutants, suggesting that an increase of APO1 activity caused the delay in the program shift to spikelet formation. In agreement with this result, ectopic overexpression of APO1 accentuated the APO1 gain-of-function phenotypes. In the apo1-D dominant alleles, the inflorescence meristem starts to increase in size more vigorously than the wild type when switching to the reproductive development phase. This alteration in growth rate is opposite to what is observed with the apo1 mutants that have a smaller inflorescence meristem. The difference in meristem size is caused by different rates of cell proliferation. Collectively, these results suggest that the level of APO1 activity regulates the inflorescence form through control of cell proliferation in the meristem.
在水稻（Oryza sativa）花序发育过程中会产生两种类型的分支，即穗轴分支（即非花分支）和小穗（即花分支）。我们之前报道过，异常穗部组织1（APO1）基因编码一种与拟南芥（Arabidopsis thaliana）异常花器官同源的含F-box蛋白，该基因可抑制穗轴分支分生组织过早转化为小穗，以确保产生一定数量的小穗。在此，我们鉴定出四个产生更多小穗的显性突变体，并发现它们是APO1的功能获得性等位基因。在所有四个突变体中，APO1的表达水平均升高，这表明APO1活性的增加导致了向小穗形成程序转变的延迟。与这一结果一致，APO1的异位过表达加剧了APO1功能获得性表型。在apo1-D显性等位基因中，当进入生殖发育阶段时，花序分生组织开始比野生型更剧烈地增大。这种生长速率的改变与在具有较小花序分生组织的apo1突变体中观察到的情况相反。分生组织大小的差异是由不同的细胞增殖速率引起的。总体而言，这些结果表明APO1活性水平通过控制分生组织中的细胞增殖来调节花序形态。
