Graduate School of Integrated Science for Life, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 Japan.
RIKEN Center for Sustainable Resource Science, RIKEN, Yokohama, Kanagawa 230-0045, Japan.
Plant Physiol. 2020 Feb;182(2):1114-1129. doi: 10.1104/pp.19.00535. Epub 2019 Nov 20.
Exposure of dark-grown (etiolated) seedlings to light induces the heterotrophic-to-photoautotrophic transition (de-etiolation) processes, including the formation of photosynthetic machinery in the chloroplast and cotyledon expansion. Phytochrome is a red (R)/far-red (FR) light photoreceptor that is involved in the various aspects of de-etiolation. However, how phytochrome regulates metabolic dynamics in response to light stimulus has remained largely unknown. In this study, to elucidate the involvement of phytochrome in the metabolic response during de-etiolation, we performed widely targeted metabolomics in Arabidopsis () wild-type and phytochrome A and B double mutant seedlings de-etiolated under R or FR light. The results revealed that phytochrome had strong impacts on the primary and secondary metabolism during the first 24 h of de-etiolation. Among those metabolites, sugar levels decreased during de-etiolation in a phytochrome-dependent manner. At the same time, phytochrome upregulated processes requiring sugars. Triacylglycerols are stored in the oil bodies as a source of sugars in Arabidopsis seedlings. Sugars are provided from triacylglycerols through fatty acid β-oxidation and the glyoxylate cycle in glyoxysomes. We examined if and how phytochrome regulates sugar production from oil bodies. Irradiation of the etiolated seedlings with R and FR light dramatically accelerated oil body mobilization in a phytochrome-dependent manner. Glyoxylate cycle-deficient mutants not only failed to mobilize oil bodies but also failed to develop thylakoid membranes and expand cotyledon cells upon exposure to light. Hence, phytochrome plays a key role in the regulation of metabolism during de-etiolation.
黑暗生长（黄化）的幼苗暴露在光照下会诱导异养到光合自养的转变（去黄化）过程，包括叶绿体和子叶中光合机器的形成。光敏色素是一种参与去黄化各个方面的红光（R）/远红光（FR）光受体。然而，光敏色素如何调节代谢动力学以响应光刺激在很大程度上仍然未知。在这项研究中，为了阐明光敏色素在去黄化过程中的代谢反应中的作用，我们对在 R 或 FR 光下去黄化的拟南芥（）野生型和光敏色素 A 和 B 双突变体幼苗进行了广泛的靶向代谢组学分析。结果表明，光敏色素在去黄化的前 24 小时对初级和次级代谢有很强的影响。在这些代谢物中，糖水平在去黄化过程中以光敏色素依赖的方式下降。与此同时，光敏色素上调了需要糖的过程。三酰基甘油作为拟南芥幼苗中糖的来源储存在油体中。糖通过脂肪酸β-氧化和乙醛酸循环从油体中的三酰基甘油提供。我们检查了光敏色素是否以及如何调节油体中的糖产生。用 R 和 FR 光照射黄化幼苗会以光敏色素依赖的方式显著加速油体的动员。乙醛酸循环缺陷突变体不仅不能动员油体，而且在暴露于光下时也不能发育类囊体膜和扩大子叶细胞。因此，光敏色素在去黄化过程中代谢调节中起着关键作用。
