水稻中新ABA转运蛋白的转录调控机制
复旦大学生命科学学院葛晓春教授课题组在水稻中发现了一种新的ABA转运蛋白，并揭示了该转运蛋白的转录调控机制，为了解水稻应对干旱胁迫的机制提供了新的线索。4月30日，研究成果以“The AWPM-19 Family Protein OsPM1 Mediates Abscisic Acid Influx and Drought Response in Rice”为题在线发表于《植物细胞》（Plant Cell）。
脱落酸（ABA）是重要的植物激素分子，其pKa值在4.7左右。在正常生长条件下，只有不到一半的ABA可以通过自由扩散的方式进行跨膜运输；在干旱等逆境胁迫下，细胞外和木质部液发生碱化，pH值上升到7.0左右，99%以上的ABA会发生解离，变成带电荷的ABA-，ABA转运蛋白对于ABA信号在体内的运输和扩散至关重要。目前，研究界已有多个ABA转运蛋白在拟南芥中被克隆，其中大部分属于ABC转运蛋白家族。
葛晓春教授课题组首次在水稻中发现了一个不同以往报道的ABA转运蛋白OsPM1, 它属于AWPM-19家族成员，在膜上能以多聚体的形式存在。研究人员发现，OsPM1对干旱和ABA处理响应非常迅速，通过表达可以增强植物的抗旱性及种子萌发对ABA的敏感性，而RNAi和KO株系则表现相反。OsPM1影响了水稻在干旱胁迫下气孔的响应性以及ABA信号传递过程。体外及体内实验均表明OsPM1可以向细胞内转运ABA，且ABA的生理活性形式（+）ABA是其底物。
进一步深入研究OsPM1的转录调控机制发现，干旱胁迫信号途径的主要转录因子OsbZIP46结合在OsPM1的启动子上，调控其在干旱胁迫下的表达。该研究系统地揭示了OsPM1的功能及调控机制，同时也表明“胁迫激素”ABA在体内的跨膜运输可能与生长素类似，存在多种结构不同的膜转运载体。
复旦大学生命科学学院葛晓春教授为本文的通讯作者，复旦大学生命科学学院博士研究生姚玲娅为本文的第一作者。相关研究工作得到了国家自然科学基金委、科技部973项目和转基因专项的资助。（来源：复旦大学生命科学学院）
The AWPM-19 Family Protein OsPM1 Mediates Abscisic Acid Influx and Drought Response in Rice
Abstract Abscisic acid (ABA) regulates plant stress responses and development. However, how the ABA signal is transmitted in response to stresses remains largely unclear, especially in monocots. In this study, we found that rice (Oryza sativa) OsPM1 (PLASMA MEMBRANE PROTEIN 1), encoded by a gene of AWPM-19 like family, mediates ABA influx through the plasma membrane. OsPM1 is predominantly expressed in vascular tissues, guard cells and mature embryos. Phenotypic analysis of overexpression, RNA interference (RNAi), and knock out (KO) lines showed that OsPM1 is involved in drought responses and seed germination regulation. 3H-(±)ABA transport activity and FRET (Fluorescence Resonance Energy Transfer) assays both demonstrated that OsPM1 facilitates ABA uptake into cells. The physiological isomer of ABA, (+)-ABA, is the preferred substrate of OsPM1. Higher ABA accumulation and faster stomatal closure in response to ABA treatment were observed in the overexpression lines compared to the wild-type control. Many ABA-responsive genes were up-regulated more in the OsPM1-overexpression lines but less in the RNAi lines compared to wild-type plants. Further investigation revealed that OsPM1 expression is regulated by the AREB/ABF family transcription factor OsbZIP46. Our results thus revealed that OsPM1 is an ABA influx carrier that plays an important role in drought responses.
原文链接：http://www.plantcell.org/content/plantcell/early/2018/04/30/tpc.17.00770.full.pdf
