Membrane Interactions of GET1 and GET2 Facilitate Fiber Cell Initiation through the Guided Entry of the TA Protein Pathway in Cotton

The guided entry of TA proteins (GET) pathway, which is responsible for the post-translational targeting and insertion of the tail-anchored (TA) protein into the endoplasmic reticulum (ER), plays an important role in physiological processes such as protein sorting, vesicle trafficking, cell apoptosis, and enzymatic reactions in which the GET1/2 complex is indispensable. However, a comprehensive study of the GET1 and GET2 genes and the GET pathway in cotton has not yet been carried out. Here, 12 GET1 and 21 GET2 genes were identified in nine representative plant species, and the phylogenetic relationships, gene structures, protein motifs, cis-regulatory elements (CREs), and temporal and spatial expression profiles were analyzed thoroughly. Our study indicated that GhGET1s and GhGET2s might be localized on ER membranes. According to expression profiling and CREs analysis, GhGET2-A02 was identified as a promising candidate for fiber cell development, interacting with two GhGET1s in the membrane, with a binding bias toward GhGET1-A06. Silencing of GhGET1-A06 or GhGET2-A02 reduced fiber initiation and elongation. In summary, our research provides important evidence for understanding the gene families and functions of GET1 and GET2 in cotton and provides clues for molecular breeding of high-quality cotton fiber varieties.尾锚定蛋白引导进入（guided entry of TA proteins, GET）通路负责将尾锚定蛋白（tail-anchored protein, TA）经翻译后靶向并插入至内质网（endoplasmic reticulum, ER），在蛋白质分选、囊泡运输、细胞凋亡及酶促反应等生理过程中发挥重要作用，其中GET1/2复合物为该通路不可或缺的核心组分。然而，目前尚未针对棉花中的GET1、GET2基因及GET通路开展系统性研究。本研究在9种代表性植物物种中鉴定得到12个GET1基因与21个GET2基因，并对其系统发育关系、基因结构、蛋白质基序、顺式调控元件（cis-regulatory elements, CREs）以及时空表达谱进行了全面深入的分析。研究结果表明，GhGET1与GhGET2家族基因可能定位于ER膜上。通过表达谱与顺式调控元件分析，本研究鉴定出GhGET2-A02可作为纤维细胞发育的潜在候选基因，其可与2个GhGET1家族蛋白在膜上相互作用，且对GhGET1-A06具有结合偏好性。沉默GhGET1-A06或GhGET2-A02会抑制纤维的起始与伸长过程。综上，本研究为解析棉花GET1、GET2基因家族及其功能提供了重要依据，同时为高品质棉花纤维品种的分子育种提供了研究线索。