Max Planck Institute for Plant Breeding Research, D-50829 Cologne, Germany;
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, 46022 Valencia, Spain; and.
Proc Natl Acad Sci U S A. 2014 Jul 1;111(26):E2760-9. doi: 10.1073/pnas.1409567111. Epub 2014 Jun 16.
In Arabidopsis thaliana environmental and endogenous cues promote flowering by activating expression of a small number of integrator genes. The MADS box transcription factor SHORT VEGETATIVE PHASE (SVP) is a critical inhibitor of flowering that directly represses transcription of these genes. However, we show by genetic analysis that the effect of SVP cannot be fully explained by repressing known floral integrator genes. To identify additional SVP functions, we analyzed genome-wide transcriptome data and show that GIBBERELLIN 20 OXIDASE 2, which encodes an enzyme required for biosynthesis of the growth regulator gibberellin (GA), is upregulated in svp mutants. GA is known to promote flowering, and we find that svp mutants contain elevated levels of GA that correlate with GA-related phenotypes such as early flowering and organ elongation. The ga20ox2 mutation suppresses the elevated GA levels and partially suppresses the growth and early flowering phenotypes of svp mutants. In wild-type plants, SVP expression in the shoot apical meristem falls when plants are exposed to photoperiods that induce flowering, and this correlates with increased expression of GA20ox2. Mutations that impair the photoperiodic flowering pathway prevent this downregulation of SVP and the strong increase in expression of GA20ox2. We conclude that SVP delays flowering by repressing GA biosynthesis as well as integrator gene expression and that, in response to inductive photoperiods, repression of SVP contributes to the rise in GA at the shoot apex, promoting rapid induction of flowering.
在拟南芥中，环境和内源性信号通过激活少数整合基因的表达来促进开花。MADS 盒转录因子短日植物（SVP）是开花的关键抑制剂，它直接抑制这些基因的转录。然而，我们通过遗传分析表明，SVP 的作用不能仅仅通过抑制已知的花整合基因来解释。为了鉴定 SVP 的其他功能，我们分析了全基因组转录组数据，结果表明，编码生长调节剂赤霉素（GA）生物合成所需酶的 GA20 氧化酶 2（GA20ox2）在 svp 突变体中上调。GA 已知能促进开花，我们发现 svp 突变体中含有升高的 GA 水平，与 GA 相关表型如早花和器官伸长相关。ga20ox2 突变抑制了升高的 GA 水平，并部分抑制了 svp 突变体的生长和早花表型。在野生型植物中，当植物暴露于诱导开花的光周期时，SVP 在茎尖分生组织中的表达下降，这与 GA20ox2 的表达增加相关。破坏光周期开花途径的突变阻止了 SVP 的这种下调和 GA20ox2 的强烈上调。我们得出结论，SVP 通过抑制 GA 生物合成以及整合基因的表达来延迟开花，并且，作为对诱导性光周期的响应，SVP 的抑制有助于在茎尖处 GA 的增加，从而促进开花的快速诱导。
