Niwa Yusuke, Ito Shogo, Nakamichi Norihito, Mizoguchi Tsuyoshi, Niinuma Kanae, Yamashino Takafumi, Mizuno Takeshi
Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-8601 Japan.
Plant Cell Physiol. 2007 Jul;48(7):925-37. doi: 10.1093/pcp/pcm067. Epub 2007 May 31.
In Arabidopsis thaliana, the flowering time is regulated through the circadian clock that measures day-length and modulates the photoperiodic CO-FT output pathway in accordance with the external coincidence model. Nevertheless, the genetic linkages between the major clock-associated TOC1, CCA1 and LHY genes and the canonical CO-FT flowering pathway are less clear. By employing a set of mutants including an extremely early flowering toc1 cca1 lhy triple mutant, here we showed that CCA1 and LHY act redundantly as negative regulators of the photoperiodic flowering pathway. The partly redundant CCA1/LHY functions are largely, but not absolutely, dependent on the upstream TOC1 gene that serves as an activator. The results of examination with reference to the expression profiles of CO and FT in the mutants indicated that this clock circuitry is indeed linked to the CO-FT output pathway, if not exclusively. For this linkage, the phase control of certain flowering-associated genes, GI, CDF1 and FKF1, appears to be crucial. Furthermore, the genetic linkage between TOC1 and CCA1/LHY is compatible with the negative and positive feedback loop, which is currently believed to be a core of the circadian clock. The results of this study suggested that the circadian clock might open an exit for a photoperiodic output pathway during the daytime. In the context of the current clock model, these results will be discussed in connection with the previous finding that the same clock might open an exit for the early photomorphogenic output pathway during the night-time.
在拟南芥中，开花时间是通过生物钟来调控的，生物钟测量日照长度，并根据外部巧合模型调节光周期CO-FT输出途径。然而，主要的生物钟相关基因TOC1、CCA1和LHY与经典的CO-FT开花途径之间的遗传联系尚不清楚。通过使用一组突变体，包括一个极早开花的toc1 cca1 lhy三突变体，我们在此表明CCA1和LHY作为光周期开花途径的负调控因子发挥冗余作用。部分冗余的CCA1/LHY功能在很大程度上，但并非绝对地，依赖于作为激活因子的上游TOC1基因。对突变体中CO和FT表达谱的检测结果表明，这个生物钟回路确实与CO-FT输出途径相关联，即便不是唯一关联。对于这种关联，某些与开花相关基因GI、CDF1和FKF1的相位控制似乎至关重要。此外，TOC1与CCA1/LHY之间的遗传联系与负反馈和正反馈回路相一致，目前认为这是生物钟的核心。本研究结果表明，生物钟可能在白天为光周期输出途径打开一个出口。在当前生物钟模型的背景下，将结合之前的发现对这些结果进行讨论，即同一个生物钟可能在夜间为早期光形态建成输出途径打开一个出口。
