Institute of Vegetable and Floriculture Science, National Agriculture and Food Research Organization (NARO), Kannondai, Tsukuba, Ibaraki, 305-8517, Japan.
Institute of Vegetable and Floriculture Science, National Agriculture and Food Research Organization (NARO), Kannondai, Tsukuba, Ibaraki, 305-8517, Japan; Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
Plant Sci. 2020 Apr;293:110417. doi: 10.1016/j.plantsci.2020.110417. Epub 2020 Jan 22.
Chrysanthemum is a typical short day (SD) flowering plant that requires a longer night period than a critical minimum duration to successfully flower. We identified FLOWERING LOCUS T-LIKE 3 (FTL3) and ANTI-FLORIGENIC FT/TFL1 FAMILY PROTEIN (AFT) as a florigen and antiflorigen, respectively, in a wild diploid chrysanthemum (Chrysanthemum seticuspe). Expression of the genes that produce these proteins, CsFTL3 and CsAFT, is induced in the leaves under SD or a noninductive photoperiod, respectively, and the balance between them determines the progression of floral transition and anthesis. However, how CsFTL3 and CsAFT are regulated to define the critical night length for flowering in chrysanthemum is unclear. In this study, we focused on the circadian clock-related gene GIGANTEA (GI) of C. seticuspe (CsGI) and generated transgenic C. seticuspe plants overexpressing CsGI (CsGI-OX). Under a strongly inductive SD (8 L/16D) photoperiod, floral transition occurred at almost the same time in both wild-type and CsGI-OX plants. However, under a moderately inductive (12 L/12D) photoperiod, the floral transition in CsGI-OX plants was strongly suppressed, suggesting that the critical night length for flowering was lengthened for CsGI-OX plants. Under the 12 L/12D photoperiod, CsAFT was upregulated in CsGI-OX plants. Giving a night break (NB) 10 h after dusk was the most effective time to inhibit flowering in wild-type plants, while the most effective time for NB was extended to dawn (12 and 14 h after dusk) in CsGI-OX plants. In wild-type plants, a red-light pulse delivered 8 or 10 h after dusk induced maximal CsAFT expression, but the length of the time period over which CsAFT could be induced by red light was extended until subjective dawn in CsGI-OX plants. Therefore, CsGI-OX plants required a longer dark period to maintain lower levels of CsAFT, and their critical night length for flowering was thus lengthened. These results suggested that CsGI has an important role in the control of photoperiodic flowering through shaping the gate for CsAFT induction by light in chrysanthemum.
菊花是一种典型的短日照（SD）开花植物，需要长于临界最短夜长才能成功开花。我们鉴定了 FLOWERING LOCUS T-LIKE 3（FTL3）和 ANTI-FLORIGENIC FT/TFL1 FAMILY PROTEIN（AFT）分别为开花促进因子和开花抑制因子，它们存在于野生二倍体菊花（Chrysanthemum seticuspe）中。CsFTL3 和 CsAFT 这两个基因的表达分别受 SD 或非诱导光周期下叶片的诱导，它们之间的平衡决定了花发育和开花的进程。然而，菊花中 CsFTL3 和 CsAFT 是如何被调控以定义临界夜长的机制仍不清楚。在这项研究中，我们关注 C. seticuspe 的生物钟相关基因 GIGANTEA（GI）（CsGI），并生成了过表达 CsGI 的转基因 C. seticuspe 植物（CsGI-OX）。在强诱导 SD（8 L/16D）光周期下，野生型和 CsGI-OX 植物的花发育几乎同时进行。然而，在中度诱导（12 L/12D）光周期下，CsGI-OX 植物的花发育受到强烈抑制，表明 CsGI-OX 植物的临界夜长变长。在 12 L/12D 光周期下，CsAFT 在 CsGI-OX 植物中上调表达。黄昏后给予 10 h 的夜间中断（NB）是抑制野生型植物开花的最有效时间，而 CsGI-OX 植物中最有效的 NB 时间延长到黎明（黄昏后 12 和 14 h）。在野生型植物中，黄昏后 8 或 10 h 给予红光脉冲可诱导最大的 CsAFT 表达，但 CsAFT 可被红光诱导的时间窗口在 CsGI-OX 植物中延长到主观黎明。因此，CsGI-OX 植物需要更长的黑暗期来维持较低水平的 CsAFT，从而延长了它们的临界夜长。这些结果表明，CsGI 通过塑造菊花中 CsAFT 诱导的光门，在光周期开花的控制中发挥重要作用。
