植物地上部通过光合作用固定碳源的过程与根系从土壤中摄取水分和养分的过程二者之间既相互促进、相互依赖，又相互矛盾、相互制约，以达到整体的协调与平衡，进而维持植物的生长发育，所以“树大根深，根深叶茂”。然而，人们对于植物如何实现地上部与根系之间协调的分子调控机制还不是十分清楚。
中国科学院遗传与发育生物学研究所傅向东课题组研究发现，拟南芥光信号途径的bZIp转录因子——HY5蛋白能够从植物地上部长距离移动至根系，自激活根系HY5基因表达，同时激活高亲和性硝酸根转运蛋白基因NRT2.1的表达，进而促进根系生长和氮吸收。进一步研究发现，地上部HY5通过增强TpS1、SWEETs等基因的表达，既促进了光合固碳又促进了光合产物从地上部运输到根系；而运输到根系的光合产物增强了HY5蛋白激活根系NRT2.1表达和氮吸收，进而维持植物碳-氮平衡。研究还发现，植物根系生长发育和氮吸收利用是受光强调控的，长距离移动的HY5蛋白整合了碳、氮代谢信号以维持植物整体在可变光照环境下的碳-氮动态平衡，保证植物生长发育的可塑性和环境适应性。该项研究揭示了植物地上部和根系间远程协调生长发育和碳-氮平衡调控的分子机制，为提高农作物氮肥利用效率提供了一种新策略。
该项研究成果于2月11日在线发表在Current Biology 杂志上，傅向东课题组陈祥彬为该论文的第一作者。该研究得到国家“973”计划和国家自然科学基金委项目的资助。
长距离运输HY5蛋白在维持植物碳-氮平衡和适应可变光环境中的作用模式图
原文摘要：
Shoot-to-Root Mobile Transcription Factor HY5 Coordinates plant Carbon and Nitrogen Acquisition
Coordination of shoot photosynthetic carbon fixation with root inorganic nitrogen uptake optimizes plant performance in a fluctuating environment [ 1 ]. However, the molecular basis of this long-distance shoot-root coordination is little understood. Here we show that Arabidopsis ELONGATED HYpOCOTYL5 (HY5), a bZIp transcription factor that regulates growth in response to light [ 2, 3 ], is a shoot-to-root mobile signal that mediates light promotion of root growth and nitrate uptake. Shoot-derived HY5 auto-activates root HY5 and also promotes root nitrate uptake by activating NRT2.1, a gene encoding a high-affinity nitrate transporter [ 4 ]. In the shoot, HY5 promotes carbon assimilation and translocation, whereas in the root, HY5 activation of NRT2.1 expression and nitrate uptake is potentiated by increased carbon photoassimilate (sucrose) levels. We further show that HY5 function is fluence-rate modulated and enables homeostatic maintenance of carbon-nitrogen balance in different light environments. Thus, mobile HY5 coordinates light-responsive carbon and nitrogen metabolism, and hence shoot and root growth, in a whole-organismal response to ambient light fluctuations.