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.     

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．     

Co-suppression of the <Emphasis Type="Italic">EIN2</Emphasis>-homology gene <Emphasis Type="Italic">LeEIN2</Emphasis> inhibits fruit ripening and reduces ethylene sensitivity in tomato

EIN2 (ethylene insensitive 2) is a very important component in the ethylene signal transduction pathway. Recently, the genomic DNA and full-length cDNA of LeEIN2 (tomato EIN2) have been isolated in our laboratory. To reveal the function of LeEIN2, transgenic tomato plants with reduced expression levels of LeEIN2 were produced. The fruit ripening and expressions of ripening-related genes encoding polygalacturonase and TomLoxB were inhibited in the LeEIN2-silenced transgenic plants compared to the wild-type Ailsa Craig. In the seedling ethylene response assay, the transgenic tomato plants with reduced LeEIN2 expression exhibited ethylene insensitivity. These results indicate that LeEIN2 plays a critical role in regulating tomato fruit ripening and is a positive regulator in ethylene signal transduction pathway.     

Signalling in Rhizobacteria-Induced Systemic Resistance in Arabidopsis thaliana

Abstract: To protect themselves from disease, plants have evolved sophisticated defence mechanisms in which the signal molecules salicylic acid, jasmonic acid and ethylene often play crucial roles. Elucidation of signalling pathways controlling disease resistance is a major objective in research on plant-pathogen interactions. The capacity of a plant to develop a broad spectrum, systemic acquired resistance (SAR) after primary infection with a necrotizing pathogen is well-known and its signal transduction pathway extensively studied. Plants of which the roots have been colonized by specific strains of non-pathogenic fluorescent Pseudomonas spp. develop a phenotypically similar form of protection that is called rhizobacteria-mediated induced systemic resistance (ISR). In contrast to pathogen-induced SAR, which is regulated by salicylic acid, rhizobacteria-mediated ISR is controlled by a signalling pathway in which jasmonic acid and ethylene play key roles. In the past eight years, the model plant species Arabidopsis thaliana was explored to study the molecular basis of rhizobacteria-mediated ISR. Here we review current knowledge of the signal transduction steps involved in the ISR pathway that leads from recognition of the rhizobacteria in the roots to systemic expression of broad-spectrum disease resistance in aboveground foliar tissues.     

The central role of PhEIN2 in ethylene responses throughout plant development in petunia

The plant hormone ethylene regulates many aspects of growth and development. Loss-of-function mutations in ETHYLENE INSENSITIVE2 (EIN2) result in ethylene insensitivity in Arabidopsis, indicating an essential role of EIN2 in ethylene signaling. However, little is known about the role of EIN2 in species other than Arabidopsis. To gain a better understanding of EIN2, a petunia (Petunia x hybrida cv Mitchell Diploid [MD]) homolog of the Arabidopsis EIN2 gene (PhEIN2) was isolated, and the role of PhEIN2 was analyzed in a wide range of plant responses to ethylene, many that do not occur in Arabidopsis. PhEIN2 mRNA was present at varying levels in tissues examined, and the PhEIN2 expression decreased after ethylene treatment in petals. These results indicate that expression of PhEIN2 mRNA is spatially and temporally regulated in petunia during plant development. Transgenic petunia plants with reduced PhEIN2 expression were compared to wild-type MD and ethylene-insensitive petunia plants expressing the Arabidopsis etr1-1 gene for several physiological processes. Both PhEIN2 and etr1-1 transgenic plants exhibited significant delays in flower senescence and fruit ripening, inhibited adventitious root and seedling root hair formation, premature death, and increased hypocotyl length in seedling ethylene response assays compared to MD. Moderate or strong levels of reduction in ethylene sensitivity were achieved with expression of both etr1-1 and PhEIN2 transgenes, as measured by downstream expression of PhEIL1. These results demonstrate that PhEIN2 mediates ethylene signals in a wide range of physiological processes and also indicate the central role of EIN2 in ethylene signal transduction.     

Members of the tomato LeEIL (EIN3-like) gene family are functionally redundant and regulate ethylene responses throughout plant development

The plant hormone ethylene regulates many aspects of growth, development and responses to the environment. The Arabidopsis ETHYLENE INSENSITIVE3 (EIN3) protein is a nuclear-localized component of the ethylene signal-transduction pathway with DNA-binding activity. Loss-of-function mutations in this protein result in ethylene insensitivity in Arabidopsis. To gain a better understanding of the ethylene signal-transduction pathway in tomato, we have identified three homologs of the Arabidopsis EIN3 gene (LeEILs). Each of these genes complemented the ein3-1 mutation in transgenic Arabidopsis, indicating that all are involved in ethylene signal transduction. Transgenic tomato plants with reduced expression of a single LeEIL gene did not exhibit significant changes in ethylene response; reduced expression of multiple tomato LeEIL genes was necessary to reduce ethylene sensitivity significantly. Reduced LeEIL expression affected all ethylene responses examined, including leaf epinasty, flower abscission, flower senescence and fruit ripening. Our results indicate that the LeEILs are functionally redundant and positive regulators of multiple ethylene responses throughout plant development.     

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．