植物蔗糖转运蛋白（SUT4）调节叶绿体光系统I的生理活性

Sucrose, the crucial sugar of the products of photosynthesis, plays an important role in transporting and distribution of assimilation in higher plant, which involved in forming yield and quality of trees. To date, the pathway concerning regulation of sucrose transporter including especially sucrose-dependent sensing and signaling remains nearly unknown. It is important scientific value to improve yield and quality of trees that study the sucrose-specific signaling pathway and then reveal the molecular mechanism of sucrose transporting and metabolism. Based on previous research results, this project mainly study the biological function involved in feedback regulation of SUT4 to photosystem I (PSI), and explore the molecular mechanism between plant sucrose perceiving and photosynthesis signaling of chloroplast. The main research contents include: 1) The molecular evidences of universal sub-cellular localization of SUT4 in chloroplast. 2) The biological function of interaction partner between SUT4 and PsaL. 3) The biological and biochemical evidences which SUT4 feedback regulates activity of photosystem I. 4) The sucrose or glucose signaling pathway initated by SUT4, etc. It is this research aim to prove the universal localization of SUT4 in chloroplast and clarify the biological value of SUT4-PsaL interaction partner and further preliminary establish the work model of PSI activity regulated by SUT4. Finally, our goal is to establish the theory foundation for organ or tissue development and genetic improvement in trees or economic forest.

蔗糖作为光合产物运输的主要形式，是形成树木生物产量和品质的物质基础。蔗糖转运蛋白(SUT)在植物光合产物的运输和分配中扮演着重要角色。然而人们对其介导的蔗糖信号感知和信号传导几乎是一无所知。所以加强蔗糖特异性的信号路径研究，对实现林木产量和品质的遗传改良具有重大科学意义。本项目在我们研究工作的基础上，以小桐子、黄粱木和拟南芥为试材，重点研究SUT4调节叶绿体PsaL活性的生理功能，探索植物蔗糖信号感知和叶绿体光系统信号关联的分子机理。主要内容包括：SUT4叶绿体亚细胞定位普遍性的分子证据；SUT4和PsaL蛋白质互作的生理功能；SUT4反馈调节PSI活性的生理生化证据；SUT4介导的蔗糖或葡萄糖信号路径等。试图证明SUT4叶绿体定位机制的普遍性规律，阐释SUT4-PsaL互作的生物学意义，构建SUT4调节PSI活性的工作模型，为树木特别是经济林器官或组织的发育和品质的遗传改良奠定理论基础。

项目围绕拟南芥、小桐子和黄梁木SUT4的蛋白定位、SUT4与PsaL的蛋白质功能互作、SUT4与PsaL互作的生理功能以及AtSUC4介导的蔗糖或葡萄糖信号反应等内容开展研究，运用植物遗传学、植物生理学及生物化学的方法从分子水平探究SUT4在蔗糖代谢尤其是蔗糖信号对植物生长发育的调节机制。我们发现，SUT4定位于叶绿体被膜，并与光系统I（PSI）亚基PsaL发生功能性互作形成SUC4-PsaL复合体共同调节PSI的光合电子传递效率。SUT4的缺失影响叶绿体发育导致基粒片层变薄，PSI电子传递效率（ETR）和P700光量子产量（Y(I)）显著下降。SUT4的mRNA转录受蔗糖或葡糖糖诱导，说明SUT4不仅能够行使蔗糖分子的转运功能，还有可能感知胞质中蔗糖浓度的变化及蔗糖的sensor的功能。此外，模式植物（拟南芥，草本）、木本油料植物（小桐子，灌木）和木本植物（黄梁木，乔木）的SUT4及SUT4s家族成员的表达模式和蛋白定位存在差异。通过本项目的实施，我们基本上可以提出叶绿体SUT4介导的蔗糖转运或蔗糖感知与调节工作模型，这为进一步探索和证明蔗糖的sensor及其信号路径奠定了坚实的基础，也为揭示植物光合效率的有效调节机制提供了一个全新的视野。