棉花GhPIN3a调控纤维细胞中生长素积累的机理

Cotton fiber, which is derived from ovule epidermis, is the major natural fiber source for global textile industry. In our previous studies, it is demonstrated that auxin accumulation in fiber initials is a key stimulus to cotton fiber initiation. The accumulation of auxin is mainly imported from the ovule outside and then distributed to fiber cells, rather than in situ auxin biosynthesis. Auxin efflux carrier GhPIN3a that is expressed in ovule outer integument (containing fiber cells) probably mediates this biological process. However, how GhPIN3a regulates auxin accumulation in cotton fiber initials is still unknown. PINs, a type of transmembrane proteins, direct auxin transport through their polar plasma-membrane localization, of which establishment and maintenance require function of endomembrane trafficking. On base of our latest work, we hypothesize that the different auxin distribution within ovule epidermis is determined by polar localization of GhPIN3a protein in fiber and non-fiber cells, and vesicle trafficking as well as the corresponding small GTP-binding proteins are possibly involved in the regulation of GhPIN3a polar localization. Hence, in this program we plan to clarify the spatiotemporal characteristic of GhPIN3a expression and protein localization in ovule epidermis, and the possible relationship between GhPIN3a and other fiber-initiation regulators. Further we will study function of the screened small GTP-binding proteins, which showed higher expression level in fiber cells than in non-fiber cells, as well as their influence on GhPIN3a polar localization. This study will benefit the knowledge of auxin-gradient establishment in single-cell cotton fibers and promote elucidation of the developmental model of cotton fiber.

棉纤维是分化的胚珠表皮细胞。生长素在纤维起始细胞中积累促进纤维产生。GhPIN3a介导的生长素极性运输参与该过程的调控，但具体的调控方式尚不明确。工作基础显示，纤维细胞中GhPIN3a在质膜上的极性定位丧失，可能造成纤维细胞中生长素的积累。囊泡运动以及相关小GTP结合蛋白调控PIN的极性定位。为此，申请人拟研究GhPIN3a在纤维起始阶段胚珠中基因、蛋白表达和定位的时空变化，阐明GhPIN3a介导胚珠中生长素梯度建立的方式。以此为基础，研究多种纤维起始因子与GhPIN3a之间的调控关系。同时突变GhPIN3a蛋白中关键氨基酸位点，分析囊泡运输在生长素积累中的作用。并研究纤维较非纤维细胞优势表达的3个小GTP结合蛋白，探究它们对GhPIN3a极性定位的影响。该研究有助于明确单细胞纤维如何通过极性运输实现生长素积累，还能完善纤维起始调控的分子机理。

棉花为纺织工业提供了主要的天然纤维来源。棉纤维由胚珠表皮细胞分化发育而来的单细胞结构。生长素在棉花纤维细胞中高浓度积累促进了纤维突起进程。因此，棉纤维为研究细胞的分化、伸长，以及单细胞生长素积累调控提供了理想材料。运输蛋白GhPIN3a介导的生长素极性运输在棉花纤维胚珠表皮的生长素浓度梯度建立中发挥重要作用。本项目针对GhPIN3a的作用机制以及受到的调控关系开展研究发现，在开花当天纤维起始的时候，GhPIN3a一方面的胚珠表皮细胞极性定位在质膜，介导生长素在胚珠表皮从株柄向合点端的运输；一方面在纤维细胞中缺失定位特征，让生长素无法流出而造成胞内生长素含量的升高。而纤维细胞中GhPIN3a定位缺失是由于细胞特异性蛋白降解所致。GhROP6是一个在纤维细胞中优势表达且激活小GTP结合蛋白，通过正向调节细胞内吞进程，进一步促进GhPIN3a在纤维细胞中的降解。超量表达GhROP6激活态能显著促进棉花纤维的伸长。通过杂交整合生长素生物合成能大幅度提高纤维产量、总产量、同时纤维长度、强度和细度都得到明显改善。