乙烯的生物合成与信号传递

乙烯是气体植物激素,它在植物的生长发育过程中有很多作用。所以了解乙烯的生物合成及其信号转导是非常重要的。二十年来,通过筛选有异于正常三重反应的突变体,人们发现了乙烯信号转导的粗略轮廓。在拟南芥中,有5个受体蛋白感受乙烯,ETR1、ERS1、ETR2、ERS2、EIN4。它们表现出功能冗余,是乙烯信号的负调控因子,在植物体内以二聚体的形式存在。ETR1的N端与乙烯结合时需要铜离子（Ⅰ）的参与。尽管已经发现ETR1有组氨酸激酶活性,而其它受体有丝氨酸/苏氨酸激酶活性,但受体参与乙烯信号转导的机制还不是很清楚。受体与Raf类蛋白激酶CTR1相互作用,CTR1是乙烯反应的负调控因子。CTR1蛋白失活使EIN2蛋白活化。EIN2的N端是跨膜结构域,与Nramp家族金属离子转运蛋白的跨膜结构域类似。EIN2的C端是一个新的未知结构域,与乙烯信号途径的下游组分相互作用。EIN3位于EIN2的下游,EIN3和EILs诱导ERF1和其它转录因子的表达,这些转录因子依次激活乙烯反应目的基因的表达,表现出乙烯的反应。EIN3受到蛋白酶体介导的蛋白降解途径的调节。由于乙烯是一种多功能的植物激素,其信号途径与其它信号途径有多重的交叉。     

乙烯信号转导的分子机制

气态植物激素乙烯在植物生长发育和应对生物及非生物胁迫过程中起着重要作用。在过去的十几年中,对模式植物拟南芥的分子遗传研究已建立从信号感知到转录调控的乙烯信号转导线性模型。拟南芥共有5个乙烯受体ETR1、ERS1、ETR2、ERS2和EIN4,目前已知ETR1定位在内质网上,与类似于Raf的蛋白激酶CTR1协同负调控乙烯反应。EIN2和EIN3／EILs位于CTR1下游,正调控乙烯反应。两个F-box蛋白EBF1和EBF2通过泛素／26S蛋白体降解途径调控EIN3的稳定性。5＇→3＇的外切核酸酶EIN5通过启动EBF1和EBF2 mRNA的降解,拮抗EBF1和EBF2对EIN3的负反馈调控。目前对于乙烯信号转导途径关键组分的生化功能和乙烯下游反应途径的了解甚少,乙烯信号转导途径与其它途径之间还存在着广泛的交叉反应,这些问题的解决将大大增加我们对乙烯信号转导途径的了解。     

乙烯信号转导的分子机制

气态植物激素乙烯在植物生长发育和应对生物及非生物胁迫过程中起着重要作用。在过去的十几年中, 对模式植物拟南芥的分子遗传研究已建立从信号感知到转录调控的乙烯信号转导线性模型。拟南芥共有5个乙烯受体ETR1、ERS1、ETR2、ERS2和EIN4, 目前已知ETR1定位在内质网上, 与类似于Raf的蛋白激酶CTR1协同负调控乙烯反应。EIN2和EIN3/EILs位于CTR1下游, 正调控乙烯反应。两个F-box蛋白EBF1和EBF2通过泛素/26S蛋白体降解途径调控EIN3的稳定性。5’→3’的外切核酸酶EIN5通过启动EBF1和EBF2 mRNA的降解, 拮抗EBF1和EBF2对EIN3的负反馈调控。目前对于乙烯信号转导途径关键组分的生化功能和乙烯下游反应途径的了解甚少, 乙烯信号转导途径与其它途径之间还存在着广泛的交叉反应, 这些问题的解决将大大增加我们对乙烯信号转导途径的了解。     

植物乙烯信号转导研究进展

过去10年,对模式植物拟南芥的分子遗传学研究建立了植物乙烯信号转导线性模型.乙烯结合到受体上,经一条MAPK级联反应和转录级联途径将信号转导而产生乙烯反应.拟南芥乙烯受体家族由5个成员构成,ETR1、ERS1、ETR2、ERS2和EIN4.乙烯受体包括三个结构域:乙烯结合结构域、组氨酸激酶结构域和反应调控结构域.乙烯受体定位于内质网,与CTR1协同负调控乙烯反应.ENI2、EIN3/EIL、ERF1依次位于CTR1下游,正调控乙烯反应.EIN3属于转录激活因子调控蛋白家族,受转录后调控.乙烯稳定EIN3结构,EBF1/EBF2促进EIN3分解.ERF1是转录调控因子家族成员之一,是EIN3/EIL的直接作用目标.     

植物激素乙烯作用机制的最新进展

气体植物激素乙烯在植物生长发育及应对胁迫的防御反应中起重要调控作用．通过20多年的研究,利用模式植物拟南芥,勾画出一条自内质网膜受体至细胞核内转录因子的线性乙烯信号转导通路．本文概述了研究乙烯信号转导的方法及乙烯信号转导的基本过程;阐述了最新发现的乙烯信号从内质网膜传递到细胞核的分子机制,即原本定位于内质网膜上的EIN2蛋白其C端被剪切之后进入细胞核,然后通过抑制EBF1／2而稳定转录因子EIN3／EIL1;根据最近多个小组报道EIN3／EIL1直接调控除乙烯响应基因之外的其他生物学过程相关基因,提出了EIN3／EIL1可以作为网络节点整合多条信号通路的新观点;通过分析不同信号通路调控EIN3／EIL1的方式,发现不仅EIN3／EIL1的蛋白稳定性受到调控,而且其转录活性还受到诸如JAZ,DELLA等转录调节因子的调控．本文展望了未来乙烯信号转导通路的研究方向与研究热点．     

乙烯受体差异性协作与Raf-like蛋白CTR1负调控的乙烯信号转导

以拟南芥为模式植物研究植物激素乙烯信号转导,在过去20年来取得了长足进展,并以遗传学与生物化学为基础建立了一个线性的信号转导途径模型．虽然这个模型基本上解释了乙烯信号组分参与的信号传递过程,但是,其中仍然存在若干问题亟待进一步研究．例如,上游的多个乙烯受体家族成员与CONSTITUTIVETRIPLE—RESPONSE1蛋白如何协同作用,下游的ETHYLENEINsENsITIVE2（EIN2）如何将乙烯信号传递给转录激活因子EIN3,以及是否存在其他的信号途径调控乙烯反应等．本文将着重阐述不同乙烯受体家族成员的协作对乙烯信号途径的差异性调控,植物利用多个乙烯受体感受乙烯的生物学意义,以及乙烯受体除了通过CTR1蛋白调节EIN2功能外,是否还存在其他的信号转导途径．     

植物SAR和ISR中的乙烯信号转导网络

乙烯作为重要的信号分子在植物SAR和ISR中发挥重要作用。受病原物和其它激发子处理后,植物体内乙烯被合成,为内质网上一个His激酶类受体家族(Ⅰ型和Ⅱ型)所感知,在铜离子的转运活性下,乙烯与受体的结合使Raf-类Ser/Thr激酶CTR1失活。在CTR1的下游,EIN2、EIN3、EIN5/AIN1、EIN6、EIN7是乙烯反应的正调节子,负责乙烯信号的传导。EIN2编码功能未知的新的膜整合蛋白,而EIN5/AIN1、EIN6和EIN7尚未从分子水平上进行鉴定。定位在核内的DNA结合蛋白EIN3,直接作用于ERF1,调节乙烯反应基因的转录,激活植物防御素和病程相关蛋白基因的表达,使植物建立抗病性反应。     

乙烯受体与信号转导成员的研究进展

综述了近几年有关乙烯受体和乙烯信号转导成员研究的最新进展,ETR1与其多基因家族的结构及在信号转导过程中的作用机理.乙烯与受体结合需要铜离子的协同作用.ETR1、CTR1、EIN2、EIN3、ERN1、ERF1等组成乙烯信号转导.     

高等植物EIN3/EILs转录因子研究进展

Ethylene-insensitive3(EIN3)和EIN3-like(EIL)蛋白是乙烯信号转导途径中重要的核转录因子。目前已经从多种高等植物中分离得到EIN3/EILs,其属于一个小的转录因子家族。这类转录因子在氨基酸序列N端高度保守,包括酸性氨基酸区、脯氨酸富集区、碱性氨基酸簇等涉及DNA结合的重要结构域,它们通过直接结合到初级乙烯反应元件(PERE)上来调节相关基因的表达。EIN3/EILs转录因子家族不同成员在不同物种间时空表达特性、表达调控模式等均有所差异,各成员主要参与调节植物对乙烯的反应,包括影响幼苗的"三重反应"、植株的生长发育等,并作为乙烯与其他信号间交叉点发挥重要作用。就近几年关于高等植物EIN3/EILs转录因子的研究进展进行综述,以期为后续研究提供理论依据。     

拟南芥乙烯信号转导机理的遗传学和化学生物学研究

乙烯信号途径的建立得益于一系列的突变体研究,EIN3是乙烯信号转导通路的核心转录因子,EIN3的蛋白质含量严格受F-BOX蛋白EBF1/EBF2的降解调控。为了进一步挖掘乙烯信号途径的新组分和深入研究EIN3及其下游的信号组分,作者筛选了四个不同来源的T-DNA库,并利用转基因植物EIN3ox作为遗传背景,进行了EIN3下游的抑制子筛选工作,还利用化学遗传学的方法筛选了四个小分子库。     

Histidine kinase activity of the ethylene receptor ETR1 facilitates the ethylene response in Arabidopsis

In Arabidopsis (Arabidopsis thaliana), ethylene is perceived by a receptor family consisting of five members. Subfamily 1 members ETHYLENE RESPONSE1 (ETR1) and ETHYLENE RESPONSE SENSOR1 (ERS1) have histidine kinase activity, unlike the subfamily 2 members ETR2, ERS2, and ETHYLENE INSENSITIVE4 (EIN4), which lack amino acid residues critical for this enzymatic activity. To resolve the role of histidine kinase activity in signaling by the receptors, we transformed an etr1-9;ers1-3 double mutant with wild-type and kinase-inactive versions of the receptor ETR1. Both wild-type and kinase-inactive ETR1 rescue the constitutive ethylene-response phenotype of etr1-9;ers1-3, restoring normal growth to the mutant in air. However, the lines carrying kinase-inactive ETR1 exhibit reduced sensitivity to ethylene based on several growth response assays. Microarray and real-time polymerase chain reaction analyses of gene expression support a role for histidine kinase activity in eliciting the ethylene response. In addition, protein levels of the Raf-like kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1), which physically associates with the ethylene receptor ETR1, are less responsive to ethylene in lines containing kinase-inactive ETR1. These data indicate that the histidine kinase activity of ETR1 is not required for but plays a modulating role in the regulation of ethylene responses. Models for how enzymatic and nonenzymatic regulation may facilitate signaling from the ethylene receptors are discussed.     

Possible modulation of Arabidopsis ETR1 N-terminal signaling by CTR1

The mitogen-activated protein kinase kinase kinase (MAPKKK) Constitutive Triple-Response1 (CTR1) plays a key role in mediating ethylene receptor signaling via its N-terminal interaction with the ethylene receptor C-terminal histidine kinase (HK) domain. Loss-of-function mutations of CTR1 prevent ethylene receptor signaling, and corresponding ctr1 mutants show a constitutive ethylene response phenotype. We recently reported in Plant Physiology that expression of the truncated ethylene receptor Ethylene Response1 (ETR1) isoforms etr11-349 and dominant ethylene-insensitive etr1-11-349, lacking the C-terminal HK and receiver domains, both suppressed the ctr1 mutant phenotype. Therefore, the ETR1 N terminus is capable of receptor signaling independent of CTR1. The constitutive ethylene response phenotype is stronger for ctr1-1 than ctr1-1 lines expressing the etr11-349 transgene, so N-terminal signaling by the full-length but not truncated ETR1 is inhibited by ctr1-1. We address possible modulations of ETR1 N-terminal signaling with docking of CTR1 on the ETR1 HK domain.     

EIN4 and ERS2 are members of the putative ethylene receptor gene family in Arabidopsis.

The Arabidopsis ethylene receptor gene ETR1 and two related genes, ERS1 and ETR2, were identified previously. These three genes encode proteins homologous to the two-component regulators that are widely used for environment sensing in bacteria. Mutations in these genes confer ethylene insensitivity to wild-type plants. Here, we identified two Arabidopsis genes, EIN4 and ERS2, by cross-hybridizing them with ETR2. Sequence analysis showed that they are more closely related to ETR2 than they are to ETR1 or ERS1. EIN4 previously was isolated as a dominant ethylene-insensitive mutant. ERS2 also conferred dominant ethylene insensitivity when certain mutations were introduced into it. Double mutant analysis indicated that ERS2, similar to ETR1, ETR2, ERS1, and EIN4, acts upstream of CTR1. Therefore, EIN4 and ERS2, along with ETR1, ETR2, and ERS1, are members of the ethylene receptor-related gene family of Arabidopsis. RNA expression patterns of members of this gene family suggest that they might have distinct as well as redundant functions in ethylene perception.     

Genetic Analysis of Ethylene Signal Transduction in Arabidopsis Thaliana: Five Novel Mutant Loci Integrated into a Stress Response Pathway

The response of Arabidopsis thaliana etiolated seedlings to the plant hormone ethylene is a conspicuous phenotype known as the triple response. We have identified genes that are required for ethylene perception and response by isolating mutants that fail to display a triple response in the presence of exogenous ethylene. Five new complementation groups have been identified. Four of these loci, designated ein4, ein5, ein6 and ein7, are insensitive to ethylene. The fifth complementation group, eir1, is defined by a novel class of mutants that have agravitropic and ethylene-insensitive roots. Double-mutant phenotypes have allowed the positioning of these loci in a genetic pathway for ethylene signal transduction. The ethylene-response pathway is defined by the following loci: ETR1, EIN4, CTR1, EIN2, EIN3, EIN5, EIN6, EIN7, EIR1, AUX1 and HLS1. ctr1-1 is epistatic to etr1-3 and ein4, indicating that CTR1 acts after both ETR1 and EIN4 in the ethylene-response pathway. Mutations at the EIN2, EIN3, EIN5, EIN6 and EIN7 loci are all epistatic to the ctr1 seedling phenotype. The EIR1 and AUX1 loci define a root-specific ethylene response that does not require EIN3 or EIN5 gene activity. HLS1 appears to be required for differential cell growth in the apical hook. The EIR1, AUX1 and HLS1 genes may function in the interactions between ethylene and other plant hormones that occur late in the signaling pathway of this simple gas.     

Heteromeric interactions among ethylene receptors mediate signaling in Arabidopsis

The gaseous hormone ethylene is perceived in Arabidopsis by a five member receptor family that consists of the subfamily 1 receptors ETR1 and ERS1 and the subfamily 2 receptors ETR2, ERS2, and EIN4. Previous work has demonstrated that the basic functional unit for the ethylene receptor, ETR1, is a disulfide-linked homodimer. We demonstrate here that ethylene receptors isolated from Arabidopsis also interact with each other through noncovalent interactions. Evidence that ETR1 associates with other ethylene receptors was obtained by co-purification of ETR1 with tagged versions of ERS1, ETR2, ERS2, and EIN4 from Arabidopsis membrane extracts. ETR1 preferentially associated with the subfamily 2 receptors compared with the subfamily 1 receptor ERS1, but ethylene treatment affected the interactions and relative composition of the receptor complexes. When transgenically expressed in yeast, ETR1 and ERS2 can form disulfide-linked heterodimers. In plant extracts, however, the association of ETR1 and ERS2 can be largely disrupted by treatment with SDS, supporting a higher order noncovalent interaction between the receptors. Yeast two-hybrid analysis demonstrated that the receptor GAF domains are capable of mediating heteromeric receptor interactions. Kinetic analysis of ethylene-insensitive mutants of ETR1 is consistent with their dominance being due in part to an ability to associate with other ethylene receptors. These data suggest that the ethylene receptors exist in plants as clusters in a manner potentially analogous to that found with the histidine kinase-linked chemoreceptors of bacteria and that interactions among receptors contribute to ethylene signal output.