植物热激转录因子在非生物逆境中的作用

The Roles of Plant Heat Shock Transcription Factors in Abiotic Stress

非生物逆境通常导致生物体内蛋白变性。热激蛋白(Hsp)作为分子伴侣协助蛋白的重新折叠、稳定、胞内运输和降解,以阻止受损蛋白的累积,维护细胞内环境的稳定。而热激蛋白的表达是通过热激转录因子(Hsfs)结合于热激蛋白基因的启动子的热激元件上(heatshockelement,HSE),以募集其它转录因子而形成转录复合体,促进热激蛋白基因的表达。植物热激转录因子比动物系统更为多样性。根据其基本的结构域,植物热激转录因子可分为三类:HsfA、HsfB、HsfC。A类Hsfs已有大量深入的研究和报道,特别是在番茄方面。HsfB和HsfC的作用尚不清楚。在其复杂的网络中,每一热激转录因子均有其独特的作用,取决于其表达模式、亚细胞定位、聚合化、活性及与其他蛋白的相互作用。在非生物逆境,尤其是热激逆境下,A类热激转录因子在调节热激蛋白的表达起着重要作用。番茄的HsfA1起着主导作用,其缺失无法被其他相近的Hsfs所取代,但在持续热逆境下,在HsfA1的配合下,HsfA2可成为主要调节因子。B类热激转录因子可作为A类Hsfs的阻抑蛋白。然而,基于对不同的单个突变体的研究,以及对酵母Hsf1致死突变体的拯救恢复,一些热激转录因子的作用又是丰余的。此外,热激蛋白也对热激转录因子起负反馈调节作用。

Abiotic stress results in protein denaturation. Heat shock proteins function as molecular chaperones in preventing the accumulation of damaged proteins to maintain cellular homeostasis by refolding, stabilization, intracellular translocation and degradation of proteins. The expression of heat shock proteins （Hsps） is regulated by the heat shock transcription factors （Hsfs） via binding to the heat shock element （HSE） of Hsps genes to recruit other transcription factors, causing the accumulation of Hsps. The diversity of the Hsf system in plants is evidently much higher than that of animals. Based on their functional domain structures, plant Hsfs can be divided into three classes, HsfA, Hsf B, and HsfC. Class A Hsfs are well characterized, especially in tomato. The functions of class B and C are still not clear. In the complex network of Hsfs, each of Hsfs has its unique role, dependent on the expression pattern, subcellular localization, oligomerization, activation, and interaction with other proteins. Class A Hsfs play an important role in regulating the Hsp genes in abiotic stress, especially in heat stress. HsfA1 in tomato act as a master regulator. The deficiency of tomato HsfA1 can not be substituted by any of other closely related Hsfs. HsfA2 might become dominant regulator under prolonged heat stress condition, although its function requires cooperate with HsfA1. Class B Hsfs might function as repressor of class A of Hsfs. However, some Hsfs are also functionally redundant based on the studies on single mutant of individual Hsf and rescue of yeast Hsfl lethal mutant. In addition, Hsps also act as negative feedback regulation of Hsfe.