曾丹琦(1997生),女,博士研究生,从事铁皮石斛生物技术育种研究。E-mail:
WOX (WUSCHEL-related homeobox)转录因子与植物发育密切相关,包括植物胚胎发育和体胚发生、花和根发育、愈伤组织的形成和维持,以及干细胞维持等过程。越来越多的研究表明WOX在植物发育过程中扮演着极其重要的角色。WOX调控植物发育的机理研究在促进植物发育以及构建植物良好表型等研究提供了突破口。主要对WOX调控植物发育的相关研究进行综述,并结合表观遗传学调控,探讨了WOX调控植物发育的过程,以期为WOX转录因子调控植物的作用机制提供启示。
WOX (WUSCHEL-related homeobox) transcription factors (TFs) are closely associated with plant development, including embryogenesis, somatic embryogenesis, flower and root development, the initiation and maintenance of callus, and stem cell maintenance in plants. Increasing studies demonstrated that WOX TFs play a crucial role in plant development. Studied on the regulatory mechanisms of WOX in plant development provide a breakthrough in promoting plant development and constructing excellent plant phenotypes. The regulation of WOX TFs in plant development was reviewed, and the developmental processes by integrating WOX and epigenetic regulation were discussed, which aimed at providing inspiration for the mechanism of WOX TFs in regulating plant development.
转录因子(transcription factors, TFs)是指能结合基因启动子从而调控基因表达的一类蛋白质分子。转录因子的调节是一个十分复杂的过程,在调控真核生物生长发育中起着重要作用。1996年,Laux等[
WOX转录因子在植物发育过程中扮演的角色非常多样化,且其调控作用非常重要。以模式植物拟南芥为例,目前发现拟南芥共有15个WOX成员,功能涉及从干细胞的维持到胚胎模式的形成,包括枝条、花分生组织形成、根形成等生长发育过程[
在植物发育过程中,胚胎发育是保证植物正常生长发育的起源和核心[
关于WOX家族成员分类的研究主要集中在进化起源上。WOX家族成员的进化情况可以根据HB同源异形结构域蛋白序列的系统发育重建进行推测,有研究表明DNA-binding motif可能起源于真核生物分化之前[
拟南芥AtWOX家族蛋白结构示意图。同源域(HD)(黄色)是该家族最突出和最明确的特征;WUS box motif (红色)在严格意义上被定义为T-L-[DEQP]-L-F-P-[GITVL]-[GSKNTCV];酸性结构域(蓝色)位于WUS-box上游大约10个残基处;EAR结构域(绿色)位于羧基末端,其结构特征是[LVI]-X-[LVI]-X-[LVI];1个假定的锌指结构域(紫色)位于HD下游,是WOX2特有的。
Schematic domain structures of WOX family proteins in
WOX转录因子的表达模式具有组织特异性。具体表现为有些WOXs成员可能在某个特定器官中高表达,但在其他器官基本检测不到,如
WOX除了在重叠的表达模式下具有功能冗余外, 也存在表达模式不同但功能具有冗余性的成员。WUS clade具有特殊的WUS box,有研究表明
综上所述,WOX转录因子表达模式的不同或相似导致了它们在功能上的多样性或冗余性。同时,功能的多样性在不同植物不同发育过程所起的作用也得到了充分体现,进一步为WOX在植物发育扮演多样化角色奠定了基础;此外,功能的冗余性增加了WOX的稳定性,例如某个WOX转录因子突变导致的缺陷或许可以由其他具有相同或相似功能的WOX弥补,保障了植物的正常生长发育。
许多同源框基因在植物发育中发挥了重要作用。WOX家族作为植物特定的转录因子家族,在植物的生长发育扮演了许多重要的角色,如植物胚胎发育和体胚发生、花发育、根发育、愈伤组织的形成和维持以及干细胞维持等。
植物胚胎发育是一个十分复杂的过程。目前有关早期胚胎发生的分子机理的研究进展缓慢,早期胚胎小且被母体细胞包围导致难以跟踪观察[
大量研究表明,WOX转录因子在植物的胚胎发育中起着关键的调控作用[
WOX转录因子在植物体胚发生扮演着重要的角色。有研究表明,WUS同源异形结构域蛋白的异位表达可以促进幼苗的体细胞胚发育[
此外,关于胚胎发育的机理,有研究表明通过调控运输和局部生长素反应可以影响胚胎发育模式[
花作为植物的重要功能器官,在植物繁殖和植物进化过程中发挥着关键的作用。研究表明WOX在植物的器官发育尤其是花器官发育具有重要作用[
尽管不同的WOX家族成员在结构上差异很大, 但部分成员在功能上存在冗余。研究表明, WOX1在调控不同植物如矮牵牛、紫花苜宿、烟草和豌豆等的花发育中是功能冗余的[
根尖分生组织是根生长发育的细胞源泉[
高等植物的根发育过程由多种信号因子调控, 如光、植物激素、环境信号等多种信号调控。植物激素对根系的调节起着重要的作用,其中WOX家族成员从植物激素角度调控植物根系发育的相关研究[
植物具有强大的发育可塑性,愈伤组织可以使植物获得再生。WOX家族成员对植物愈伤组织的形成和维持起着关键的调控作用。研究表明,B型ARR-HD-ZIPⅢ复合体可以诱导
尽管对植物细胞全能性的研究历史很悠久,但其分子机制在很大程度上仍然是模糊的。目前关于WOX家族影响植物愈伤组织的研究不多,其中比较热门的是结合组学技术的研究。选择WOX转录因子作为切入点进行分析进而实现精准定位的组学技术,或许可以解析WOX在愈伤组织表达情况,进而揭示调控愈伤组织的相关机制。
干细胞是一类未分化和持续分裂的细胞群,植物干细胞实为茎尖分生组织(SAM)、根尖分生组织(RAM)等各类分生组织,可以高效率地利用生物反应器生产活性物质,在药品(下游制药)、食品(功能性食品)以及化妆品行业具有广阔的应用前景[
大量研究发现WOX家族成员在植物未分化细胞的发生和维持具有重要的作用。WUS是WOX家族的创始成员,可以促进干细胞的识别和维持[
植物中干细胞群体的自我更新是动态的,涉及了复杂的调控网络。WUS蛋白是调控植物茎端干细胞的核心因子,以WOX转录因子功能为中心的干细胞生态位的遗传机制的本质一直难以捉摸,目前有关干细胞生态位中保守的WOX功能的分子联系以及WOX如何与其他因子相关作用形成调控网络只有少量研究。因此,深入研究WOX蛋白及其互作因子,对于解析植物干细胞发育过程很关键。有研究表明,拟南芥
综上所述,WOX转录因子可以调控植物的干细胞命运。WOX具有保守性功能[
WOX转录因子基因在植物生长发育过程中的调控功能。Auxin: 生长素;CK: 细胞分裂素; ARRs: 拟南芥反应调节因子;LBD16: 侧器官边界-结构域16。实线箭头表示直接调节,虚线箭头表示间接调节,其机制尚不清楚。
Regulation functions of WOX TFs during plant growth and development. Auxin: Auxin; CK: Cytokinin; ARRS: ARABIDOPSIS RESPONSE REGULATORS; LBD16: LATERAL ORGAN BOUNDARIES-DOMAIN 16 (LBD16). Arrows with a solid line indicate direct regulation and arrows with dotted lines show indirect regulation, and its mechanism is not clear.
WOX转录因子参与植物的发育如胚胎发育、体胚发生,以及植物花、叶、根的发育,同时在愈伤组织形成中发挥重要作用。尽管大多数WOX亚家族的结构明显不同(如外显子数差异、每个亚家族特有的保守肽基序等),但这些亚家族中许多蛋白质确实存在共享一些祖先的共同功能现象,如功能重叠、功能互补等,这或许是研究WOX家族成员进化历程的突破口。其中,有些WOX家族成员尽管表达模式不同,但它们的蛋白质序列保持着相似的能力即功能重叠,说明了WOX家族成员功能的进化可能主要通过表达模式的改变。然而,WOX家族不同成员的功能互补主要通过功能多样性的多种成分调控元件实现,暗示WOX功能的进化可能是氨基酸序列变化起作用。
植物和动物最大的区别之一是植物不能移动, 因此,为了应对复杂多变的生长环境,植物必须进化出独特的信号机制来完成器官形成和发育,主要方式之一是通过胞间连丝进行细胞间运输,相关的移动分子包括蛋白、植物激素等。其中,蛋白大多数是非细胞自主性转录因子,植物中非细胞自主性转录因子参与了植物发育调控网络。在植物生长发育的过程中,WOX家族成员作为植物特有的转录因子家族,可以调控植物生长发育的多个环节,在调控过程中也涉及到了细胞分裂素、生长素等生长素的信号传导以及反应调节因子等多种因素,是一个极其复杂的调控网络。虽然前人已经进行了大量的相关研究,但是很多机理如这些因素在植物发育过程中“何时”、“何地”进行相互作用至今没有定论。
此外,从表观遗传角度研究
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