糖酵解途径中磷酸甘油酸激酶参与花粉管极性调控的研究

Pollen tube growth represents an attractive model system to study polarized cell growth. Polarized elongation of pollen tube requires intensive vesicle trafficking and dynamic signaling networks, which are high energy-demanding processes. So far,the understanding of pollen energy metabolism is limited to the maintanace of cell elongation, while little is known about their roles in polarity regulation.We have previously identified a pgk1 mutant of Arabidopsis with pollen tube polarity defects. PGK1 is a phosphoglycerate kinase, which is a key enzyme in glycolysis. Our results showed that the F-actin dynamic was not affected in pgk1 mutant, while vesicle trafficking was apparently disrupted. Furthermore, pgk1 mutant phenotype was enhanced by ren1 mutant, and REN1 protein localizaiton was affected in pgk1. These results indicated that PGK1 genetically interacts with ROP signaling pathway, the key regulator of pollen tube polarity.We proposed a hypothesis that PGK1, and the glycolysis pathway, not only functions in fundamental enerngy metablism, but also play a role in the pollen signaling network that coordinates the cellular processes required for polarity regulation. We have designed a series of experiments to further invastigate the molecular mechanism of PGK1 regulated pollen tube polarity.Our researches will provide new insights into the function of energy mechabolism in polarity regualtion.

植物花粉管是研究细胞极性生长的理想模式系统。花粉管的极性生长依赖于高度活跃的细胞转运系统和信号调控网络，因此对ATP能量供应具有很高的要求。目前对花粉管能量代谢途径的认识主要是基础代谢功能和维持生长，而对其如何参与极性信号调控尚不清楚。本课题组在前期研究中发现，拟南芥能量代谢糖酵解途径中一个关键酶PGK1的突变，会造成花粉管极性缺陷。进一步的研究结果表明PGK1可能影响囊泡运输，并与花粉管极性关键调控因子REN1有遗传互作。我们推测PGK1在花粉管中除了基础的代谢功能，还具有特异性的细胞转运调控功能。我们计划开展一系列细胞生物学和生物化学试验，以明确PGK1是否通过能量代谢调功能控花粉管极性，阐明pgk1突变体花粉管极性缺陷的细胞学原理，并探索糖酵解途径如何参与调控花粉管极性信号网络。本项目以糖酵解途径在花粉管中的新功能为研究对象，为植物极性调控机制研究提供了新的切入点。

细胞极性是所有真核生物的最基本的生命行为之一，细胞极性建立的模式也具有共通之处，首先是接收外界信号确立极性点，然后是放大信号并且维持极性点。虽然不同细胞在极性点的复合物差异很大，但有一共通之处，就是以Rho小G蛋白为核心的信号通路在其中发挥关键作用。细胞活动必须与能量代谢状态相适应，动物中能量代谢的感应因子5' AMP-activated protein kinase（AMPK）能够调节细胞极性，用糖酵解抑制剂2-脱氧葡萄糖抑制能量代谢能导致体外培养的非极性癌细胞极性化。体外实验证明糖酵解中间产物丰度能够影响AMPK活性。这里的问题是能量代谢和细胞极性这两种保守的细胞活动之间的联系是不是保守的？在本项目资助下，研究发现糖酵解酶活性缺陷的突变型mPGKc不能互补pgkc-1的花粉管极性表型，PGK上游的甘油醛-3-磷酸脱氢酶（Glyceraldehyde-3-phosphate dehydrogenase, GAPDH）的突变体gapc1-1/2-1以及GAPDH抑制剂处理的野生型花粉管也具有类似pgkc-1的花粉管表型，说明糖酵解能够调节花粉管细胞极性。pgkc-1突变体和GAPDH抑制剂处理的野生型花粉管中微丝和外排囊泡在顶端过度聚集，与此相对应，Rho小G蛋白ROP1在花粉管顶端被过度激活。然而作为ROP1 的GTP酶激活蛋白（RopGAP）的REN1却不能在花粉管顶端聚集以抑制ROP1的活性。说明该条负反馈调节通路被pgkc-1突变体和GAPDH抑制剂破坏，其具体机制还不清楚。本研究给出了遗传学证据说明糖酵解能够调节细胞极性，而且是通过调控在真核生物中保守的Rho 小G蛋白信号通途调控细胞极性。受项目资助，申请人以通讯作者第一标注发表PLoS Genetics1篇,Plant Journal1篇，多次参加国内外重要学术会议及参加学术交流，培养博士研究生2名，硕士研究生1名。