光信号与G蛋白信号互作调控植物光形态建成和气孔发育的分子机制研究

Light is an important environmental cue, and G protein acts as an important internal signal of plants, both of which are involved in the regulation of multiple critical plant developmental processes such as photomorphogenesis and stomatal development. To date, whether light and G protein signaling cross-talks, and how they cross-talks remain largely unknown. Our preliminary data indicate that the blue light photoreceptor CRY1 and red light photoreceptor phyB physically interact with the β subunit of G protein, AGB1, respectively, and that AGB1 physically interacts with the critical positive and negative regulators of photomorphogenesis, HY5 and PIFs, and the pivotal positive regulator of stomatal development, SPCH, respectively, all of which are transcriptional factors. Based on these findings, we are planning to utilize the combined approaches of plant genetics, physiology, biochemistry and molecular biology to explore: (1) whether light signaling represses G protein signaling through repression of AGB1 by CRY1 and phyB, respectively; (2) whether G protein signaling suppresses light signaling through suppression of HY5 transcriptional activity and/or its binding to the promoters of target genes by AGB1, and promotion of PIFs transcriptional activity and/or their binding to the promoters of target genes by AGB1, respectively; (3) whether light and G protein signaling integrate through CRY1/phyB-AGB1-SPCH pathway to regulate stomatal development. The antagonistic regulation mechanism of the internal and external signals of plants likely revealed through this study is in favor of plants to finetune their developmental status according to the dynamic changes of the internal and external signals, thus to better get adapted to the environment.

光信号和G蛋白信号分别是重要的环境信号和植物内在的重要信号，它们都调控光形态建成和气孔发育。目前对于这两种信号之间是否互作、如何互作的机制尚不清楚。我们前期的工作表明，光受体CRY1和phyB分别与G蛋白β亚基AGB1发生互作；AGB1分别与正调控光形态建成和负调控光形态建成的关键转录因子HY5和PIFs，以及促进气孔发育的关键转录因子SPCH存在互作。在此基础上，我们将进一步研究光信号是否通过CRY1和phyB与AGB1发生依赖于光的互作来抑制其功能，从而抑制G蛋白信号转导；G蛋白信号是否通过AGB1与HY5和PIFs的互作分别抑制HY5和促进PIFs的转录活性，来抑制光信号转导；光和G蛋白信号是否通过CRY1/phyB-AGB1-SPCH通路进行整合并调控气孔发育。这种植物内、外信号间相互“制衡”的机制有利于植物根据内、外信号的动态变化，来精细调控其生长发育状态，以更好地适应环境。

光不仅是光合作用的能量来源，也是调控植物生长发育的信号来源。光信号通过多个光受体介导的信号转导途径来实现对植物光形态建成的调控。一方面光信号可以通过蓝光受体CRY1和红光受体被光激活后与COP1/SPA复合体互作抑制COP1的E3泛素连接酶活性，促进光形态建成的正调控因子HY5的蛋白积累，从而促进光形态建成；另一方面，红光受体光敏素phyB被光激活后与关键的光形态建成的负调控因子PIFs互作，促进PIFs蛋白的磷酸化和泛素化降解，从而促进光形态建成；G蛋白是广泛存在于真核生物中的一类重要信号转导蛋白，由α、β和γ三个不同亚基组成。先前的研究发现拟南芥G蛋白β亚基AGB1负调控光形态建成。但光信号与植物G蛋白信号是否直接互作来优化对植物光形态建成的调控目前尚不清楚。通过该项目研究，揭示了拟南芥蓝光受体CRY1和红光受体phyB与G蛋白β亚基AGB1互作拮抗调控光形态建成的机制。发现AGB1通过与HY5的直接互作来抑制其DNA结合能力，以及与PIF的直接互作来抑制PIF的磷酸化和蛋白降解，来抑制光信号。发现蓝光信号通过CRY1与AGB1的直接互作促进AGB1与HY5的解离来抑制AGB1的功能，从而抑制G蛋白信号。揭示了G蛋白信号通过AGB1与PIF的互作，抑制phyB与PIF的互作而抑制PIF的磷酸化和蛋白降解，而phyB通过抑制AGB1与PIF的互作来解除AGB1对PIF的“保护”作用来促进PIF的磷酸化和蛋白降解，从而抑制G蛋白信号。该研究表明，在蓝光条件下，通过CRY1-AGB1-HY5信号通路，可以实现对CRY1介导的蓝光信号与AGB1介导的G蛋白信号的效应的平衡，从而优化其光形态建成；在红光条件下，通过phyB-AGB1-PIF信号通路，使phyB和AGB1通过拮抗彼此与PIF的结合来对PIF3的蛋白稳定性进行动态调控，使植物能够平衡光信号和G蛋白信号，从而优化其光形态建成。上述研究结果不仅具有重要的科学价值，还将为通过调控光信号和G蛋白信号动态平衡，来提高农作物对光信号和G蛋白信号的有效利用从而优化生长发育性状提供理论基础。