Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland.
Curr Biol. 2013 Oct 7;23(19):1934-8. doi: 10.1016/j.cub.2013.07.079. Epub 2013 Sep 26.
Phototropism is an adaptive response allowing plants to optimize photosynthetic light capture. This is achieved by asymmetric growth between the shaded and lit sides of the stimulated organ. In grass seedlings, the site of phototropin-mediated light perception is distinct from the site of bending; however, in dicotyledonous plants (e.g., Arabidopsis), spatial aspects of perception remain debatable. We use morphological studies and genetics to show that phototropism can occur in the absence of the root, lower hypocotyl, hypocotyl apex, and cotyledons. Tissue-specific expression of the phototropin1 (phot1) photoreceptor demonstrates that light sensing occurs in the upper hypocotyl and that expression of phot1 in the hypocotyl elongation zone is sufficient to enable a normal phototropic response. Moreover, we show that efficient phototropism occurs when phot1 is expressed from endodermal, cortical, or epidermal cells and that its local activation rapidly leads to a global response throughout the seedling. We propose that spatial aspects in the steps leading from light perception to growth reorientation during phototropism differ between grasses and dicots. These results are important to properly interpret genetic experiments and establish a model connecting light perception to the growth response, including cellular and morphological aspects.
向光性是一种适应性反应，使植物能够优化光合光捕获。这是通过刺激器官的受光侧和遮光侧之间的不对称生长来实现的。在草幼苗中，光受体介导的光感知部位与弯曲部位不同；然而，在双子叶植物（例如拟南芥）中，感知的空间方面仍然存在争议。我们使用形态学研究和遗传学表明，即使没有根、下胚轴、下胚轴顶端和子叶，也可以发生向光性。光受体 1（phot1）的组织特异性表达表明光感应发生在上胚轴，并且在胚轴伸长区表达 phot1 足以使正常的向光性反应发生。此外，我们表明，当 phot1 从内胚层、皮层或表皮细胞表达时，有效向光性发生，并且其在胚轴伸长区的局部激活迅速导致整个幼苗的全局反应。我们提出，在从光感知到向光性生长重定向的步骤中，光受体介导的空间方面在禾本科植物和双子叶植物之间存在差异。这些结果对于正确解释遗传实验和建立连接光感知与生长反应的模型（包括细胞和形态方面）非常重要。
