Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.
IFEVA, Facultad de Agronomia, Universidad de Buenos Aires and CONICET, Av. San Martin 4453, 1417 Buenos Aires, Argentina.
Curr Biol. 2016 Dec 19;26(24):3280-3287. doi: 10.1016/j.cub.2016.10.001. Epub 2016 Nov 23.
Phototropism is an asymmetric growth response enabling plants to optimally position their organs. In flowering plants, the phototropin (phot) blue light receptors are essential to detect light gradients. In etiolated seedlings, the phototropic response is enhanced by the red/far-red (R/FR)-sensing phytochromes (phy) with a predominant function of phyA. In this study, we analyzed the influence of the phytochromes on phototropism in green (de-etiolated) Arabidopsis seedlings. Our experiments in the laboratory and outdoors revealed that, in open environments (high R/FR ratio), phyB inhibits phototropism. In contrast, under foliar shade, where access to direct sunlight becomes important, the phototropic response was strong. phyB modulates phototropism, depending on the R/FR ratio, by controlling the activity of three basic-helix-loop-helix (bHLH) transcription factors of the PHYTOCHROME INTERACTING FACTORs (PIFs) family. Promotion of phototropism depends on PIF-mediated induction of several members of the YUCCA gene family, leading to auxin production in the cotyledons. Our study identifies PIFs and YUCCAs as novel molecular players promoting phototropism in photoautotrophic, but not etiolated, seedlings. Moreover, our findings reveal fundamental differences in the phytochrome-phototropism crosstalk in etiolated versus green seedlings. We propose that in natural conditions where the light environment is not homogeneous, the uncovered phytochrome-phototropin co-action is important for plants to adapt their growth strategy to optimize photosynthetic light capture.
向光性是一种不对称生长反应，使植物能够最佳地定位其器官。在开花植物中，光受体（phot）蓝光照体对于检测光梯度至关重要。在黄化幼苗中，光的向光性反应增强了红光/远红光（R/FR）感知的光敏色素（phy），phyA 的功能主要是 phyA。在这项研究中，我们分析了光敏色素对绿色（去黄化）拟南芥幼苗向光性的影响。我们在实验室和户外进行的实验表明，在开放环境（高 R/FR 比）中，phyB 抑制向光性。相比之下，在叶子遮荫下，直接阳光变得重要，向光性反应强烈。phyB 通过控制 PHYTOCHROME INTERACTING FACTORS（PIFs）家族的三个基本螺旋-环-螺旋（bHLH）转录因子的活性，根据 R/FR 比来调节向光性。向光性的促进取决于 PIF 介导的几个 YUCCA 基因家族成员的诱导，导致子叶中生长素的产生。我们的研究确定了 PIFs 和 YUCCAs 作为促进光自养但非黄化幼苗向光性的新的分子参与者。此外，我们的发现揭示了黄化与绿色幼苗中光敏色素-向光性相互作用的基本差异。我们提出，在光环境不均匀的自然条件下，未被掩盖的光敏色素-光受体协同作用对于植物适应其生长策略以优化光合光捕获非常重要。
