棉花TERMINAL FLOWER1亚家族基因调控开花转变与株型发育的分子机制

Initiation of flowering is an important developmental process during life cycle of cotton. Flowering time and plant architecture have a significant correlation with yield and quality traits in cotton. Plant TERMINAL FLOWER1 (TFL1) is a key regulator of inflorescence architecture, by controlling shoot meristem identity and flowering time. TFL1 homologs in different plants have conserved functions, but also have specific functions. However, understanding of molecular mechanism of TFL1 is not clear, especially in polyploid plants. We have identified two TFL1 paralogs in upland cotton (G. hirsutum L.) by whole genome analysis, which were named as GhTFL1a and GhTFL1b respectively. Preliminary function analyses showed that TFL1 homologs in cotton significantly extended vegetative growth, delayed flowering, and altered branch types; there were functional differences between the two. In this project, we will generate mutants using gene edition technology to explore gene functions. We will screen the TFL1 interaction proteins of upstream and downstream to analyze the similarities and differences. By using molecular biology experiments, we will analyze the regulation ways of the two cotton TFL1 genes on flowering transition and plant architecture establishment, and investigate the mechanism of variation in cotton evolution, and explore the potential utilization of genes in cotton breeding. Our research will provide genetic support for the molecular breeding of cotton.

开花转变是棉花重要的发育过程，开花早晚、株型结构与纤维产量及品质显著相关。高等植物的TERMINAL FLOWER1 (TFL1)基因调控开花转变和分生组织的命运，对植物形态结构起着关键的调控作用。不同植物TFL1基因的功能既保守，又有物种特异性，但目前多倍体植物中TFL1亚家族基因的功能机制还不清楚。前期从陆地棉中克隆了2个TFL1同源基因GhTFL1a和GhTFL1b，初步的研究表明二者促进无限生长、延迟开花、改变分枝结构，但存在功能分化。本项目拟通过基因编辑技术创制基因突变体分析基因功能，筛选互作蛋白、探索TFL1上下游蛋白的异同，结合分子生物学实验分析2个TFL1基因在棉花开花转变及株型建立中的功能机制与调控方式，探讨基因在棉花育种中的潜在利用价值，本研究将对棉花的分子改良育种提供支持。

过量表达棉花3个反花素同源基因GhTFL1-1、GhTFL1-2和GhSP，均能够促进拟南芥的营养生长，抑制开花转变；基因沉默后促进棉花早花早熟，但GhSP基因沉默终止茎秆的无限生长，导致棉花主茎自封顶。海岛棉Gbsp113Ser突变产生零式型果枝，陆地棉Ghsp73Asn突变产生丛生铃，但是植株顶端仍然保持无限生长状态。GhTFL1-1、GhTFL1-2和GhSP均能与GhFD1、Gh14-3-3在细胞体内互作，但是Ghsp73Asn和Gbsp113Ser突变蛋白不能与GhFD1互作。基因编辑成花素基因GhFT植株表现出无限生长、顶端成簇和顶端叶片边缘锯齿状。通过酵母文库筛选鉴定了一个与GhFT/TFL1互作的蛋白Gh14-3-3，二者在细胞质和细胞核中均存在互作。棉花基因组中含有5个bZIP转录因子GhFD，进化中分为2个亚类，GhFD1/2与AtFD同源基因具有较高的相似性，GhFD3/4/5为锦葵属植物所特有。GhFT、Gh14-3-3和5个GhFD蛋白均能够在细胞核中互作，形成FAC复合体，依据GhFD的不同，参与调控棉花的开花时间和根系发育。在茎尖分生组织中GhFT–Gh14-3-3–GhFD1/2复合体能够激活花身份同源基因APETALA1表达，从而促进棉花开花转变；另一方面在根中GhFT–Gh14-3-3–GhFD3/4/5复合体激活植物侧根发育关键基因AUXIN RESPONSE FACTOR 19的表达，进而促进棉花侧根发育。此外全基因组鉴定了棉花82个14-3-3 (GRF)基因家族成员，Y2H和BiFC实验表明GhGRF3/6/9/14/15、GhFT、GhFD在细胞核中互作形成GhFT–GhGRF3/6/9/14/15–GhFD复合体。综上，本项目主要解析了陆地棉FT/TFL1基因调控棉花开花、株型调控中的分子功能。FT/TFL1会和不同FD、14-3-3蛋白形成不同的FAC，FAC的功能不仅取决于14-3-3也取决于招募的FD蛋白。GhFT–Gh14-3-3–GhFDs复合物调控模块的解析，从分子水平上揭示了棉花开花转变的内在机理以及FAC功能的多样性机制。本研究初步阐明了棉花开花调控和株型建立的分子调控机制，发现“成花素-反花素”系统分子模块能够精密调控棉花多方面的生长发育，为棉花分子育种提供理论基础和指导。