拟南芥AtNHX5和AtNHX6调控生长发育的分子机理

Plant Na+,K+/H+ antiporters (NHX) are critical players in cellular pH and ion homoeostasis, and play essential roles in many aspects of growth and development in plants. AtNHX5 and AtNHX6 which localize in the Golgi/TGN are members of the endosomal antiporters. A recent report indicates that AtNHX5 and AtNHX6 control Arabidopsis growth and development; AtNHX5 and AtNHX6 are critical for cell expansion, cell proliferation, pH homeostasis, and protein trafficking in Arabidopsis (Bassil et al., 2011). However, the molecular mechanism underlying the function of AtNHX5 and AtNHX6 in regulating plant growth and development remains largely unknown. Meanwhile, a new type of the auxin efflux carrier PIN proteins, including PIN5, PIN6 and PIN8, is found to be localized in the endoplasmic reticulum. Currently, the ER-localized PIN proteins (ER-PINs) have been demonstrated to function in auxin homeostasis as well as in plant growth and development. But their mode of action and regulating mechanism are not clear (Adamowski and Friml, 2015). In this study, by linking plant NHXs with PINs, we aim to demonstrate that AtNHX5 and AtNHX6 control plant growth and development through regulating the cellular auxin homeostasis maintained by the ER-PINs. We plan to study the role of AtNHX5 and AtNHX6 in regulating the activity and function of ER-PINs using molecular genetics and cell biological methods and techniques. Our study will pave the way for the understanding of the mechanism underlying the function of AtNHX5 and AtNHX6 in regulating plant growth and development as well as the mode of action of ER-PINs and their regulating mechanism in plants.

植物Na+,K+/H+反向交换体是调节细胞pH和离子平衡的重要蛋白，在植物生长发育的许多方面起着重要的作用。近年研究发现，AtNHX5和AtNHX6调控着植物的生长发育过程；它们在细胞扩展、细胞增殖、pH平衡和蛋白质运输等过程中起着重要的作用。然而目前对于AtNHX5和AtNHX6调控植物生长发育的分子机理尚无任何报道。同时，拟南芥存在一类定位于内质网的生长素运输蛋白PIN蛋白（ER-PINs）。目前关于ER-PINs调节细胞生长素平衡和植物生长发育的功能已有报道，但是关于ER-PINs 的作用机制和调节机理还很不清楚。本项目将二者联系起来，试图证明AtNHX5和AtNHX6是通过调控ER-PINs调节细胞生长素的平衡，进而调节植物的生长发育过程。本项目的研究将为认识AtNHX5和AtNHX6调控植物生长发育的分子机理，阐明ER-PINs的作用机制和调节机理奠定理论基础。

植物Na+,K+/H+反向交换体是调节细胞pH和离子平衡的重要蛋白，在植物生长发育的许多方面起着重要的作用。近年研究发现，AtNHX5和AtNHX6调控着植物的生长发育过程；它们在细胞扩展、细胞增殖、pH平衡和蛋白质运输等过程中起着重要的作用。然而目前对于AtNHX5和AtNHX6调控植物生长发育的分子机理尚无任何报道。拟南芥存在一类定位于内质网的生长素运输蛋白PIN蛋白(ER-PINs)。目前关于ER-PINs调节细胞生长素平衡和植物生长发育的功能已有报道，但是关于ER-PINs的功能和调节机理还很不清楚。本项目试图证明AtNHX5和AtNHX6是通过调控ER-PINs调节细胞生长素的平衡，进而调节植物的生长发育过程。我们采用分子遗传学和细胞生物学技术方法，研究了AtNHX5和AtNHX6调节生长素转运蛋白ER-PIN蛋白PIN5，PIN6和PIN8的功能及机理。我们发现nhx5nhx6双突变体生长素平衡发生变化，表现出生长素缺陷的生长表型。遗传分析表明，PIN5的功能依赖于AtNHX5和AtNHX6。我们发现AtNHX5和AtNHX6与PIN5之间没有直接的相互作用；AtNHX5和AtNHX6通过其离子转运活性产生的pH调节PIN5的功能。PIN8在雄配子体中特异表达，调控着花粉的生长发育。我们发现nhx5nh6雄蕊生长素分布减少，花粉发育正常率降低，花粉萌发率降低，花粉管伸长减小，传粉率降低。遗传分析表明，PIN8的功能依赖于AtNHX5和AtNHX6，表明AtNHX5和AtNHX6可能通过调节PIN8的功能调节花粉的生长发育。我们的遗传分析结果显示，PIN6的功能依赖于AtNHX5和AtNHX6。我们还发现AtNHX5和AtNHX6与PIN6共同调控着细胞生长素的稳态平衡；AtNHX5和AtNHX6是通过其离子转运活性调节PIN6的功能。我们还分析了NHX的结构功能，离子转运特性以及调节蛋白质运输的功能；比较了NHX5/6与KEA4/5/6两类内膜系统Na+,K+/H+反向转运蛋白的离子转运特性及生物学功能。本项目的结果表明，AtNHX5和AtNHX6是通过调控ER-PINs调节细胞生长素的平衡，进而调节植物的生长发育过程。本项目的研究结果为认识AtNHX5和AtNHX6调控植物生长发育的分子机理，阐明ER-PINs的功能和调节机理奠定理论基础。