Blázquez M A, Weigel D
Plant Biology Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.
Plant Physiol. 1999 Aug;120(4):1025-32. doi: 10.1104/pp.120.4.1025.
Phytochromes and gibberellins (GAs) coordinately regulate multiple aspects of Arabidopsis development. Phytochrome B (PHYB) promotes seed germination by increasing GA biosynthesis, but inhibits hypocotyl elongation by decreasing the responsiveness to GAs. Later in the life cycle of the plant, PHYB and GAs have opposite effects on flowering. PHYB delays flowering, while GAs promote flowering, particularly under noninductive photoperiods. To learn how PHYB and GAs interact in the control of flowering, we have analyzed the effect of a phyB mutation on flowering time and on the expression of the floral meristem-identity gene LFY (LEAFY). We show that the early flowering caused by phyB correlated with an increase in LFY expression, which complements our previous finding that GAs are required for activation of LFY under noninductive photoperiods (M.A. Blázquez, R. Green, O. Nilsson, M.R. Sussman, D. Weigel [1998] Plant Cell 10: 791-800). Since phyB did not change the GA responsiveness of the LFY promoter and suppressed the lack of flowering of severe GA-deficient mutants under short days, we propose that PHYB modulates flowering time at least partially through a GA-independent pathway. Interestingly, the effects of PHYB on flowering do not seem to be mediated by transcriptional up-regulation of genes such as CO (CONSTANS) and FT (Flowering locus T), which are known to mediate the effects of the photoperiod-dependent floral-induction pathway.
光敏色素和赤霉素（GAs）协同调控拟南芥发育的多个方面。光敏色素B（PHYB）通过增加赤霉素生物合成来促进种子萌发，但通过降低对赤霉素的响应性来抑制下胚轴伸长。在植物生命周期的后期，PHYB和赤霉素对开花有相反的影响。PHYB延迟开花，而赤霉素促进开花，特别是在非诱导光周期条件下。为了了解PHYB和赤霉素在开花控制中是如何相互作用的，我们分析了phyB突变对开花时间和花分生组织特征基因LFY（LEAFY）表达的影响。我们发现，phyB导致的早花与LFY表达增加相关，这补充了我们之前的发现，即在非诱导光周期条件下，赤霉素是激活LFY所必需的（M.A. Blázquez、R. Green、O. Nilsson、M.R. Sussman、D. Weigel [1998] 《植物细胞》10: 791 - 800）。由于phyB没有改变LFY启动子对赤霉素的响应性，并且在短日照条件下抑制了严重赤霉素缺陷突变体不开花的现象，我们提出PHYB至少部分地通过一条不依赖赤霉素的途径来调节开花时间。有趣的是，PHYB对开花的影响似乎不是由CO（CONSTANS）和FT（Flowering locus T）等基因的转录上调介导的，已知这些基因介导光周期依赖的成花诱导途径的作用。
