花衰老相关的乙烯信号转导基因研究进展

乙烯在许多切花衰老过程中起着重要的调节作用,不同的植物乙烯信号转导组分在花衰老过程中有不同的转录调节特性。根据乙烯信号转导标准模式,通过调节乙烯信号转导基因表达能够调控花对乙烯的敏感性,深入研究乙烯信号转导机制;可能有多条途径可延缓切花衰老。综述了香石竹和月季等几种观赏植物在花衰老过程中乙烯受体和乙烯信号转导基因表达及特性。     

Myo-Inositol-Dependent Sodium Uptake in Ice Plant

The phytohormone ethylene regulates many aspects of plant growth, development, and environmental responses. Much of the developmental regulation of ethylene responses in tomato (Lycopersicon esculentum) occurs at the level of hormone sensitivity. In an effort to understand the regulation of ethylene responses, we isolated and characterized tomato genes with sequence similarity to the Arabidopsis ETR1 (ethylene response 1) ethylene receptor. Previously, we isolated three genes that exhibit high similarity to ETR1 and to each other. Here we report the isolation of two additional genes, LeETR4 and LeETR5, that are only 42% and 40% identical to ETR1, respectively. Although the amino acids known to be involved in ethylene binding are conserved, LeETR5 lacks the histidine within the kinase domain that is predicted to be phosphorylated. This suggests that histidine kinase activity is not necessary for an ethylene response, because mutated forms of both LeETR4 and LeETR5 confer dominant ethylene insensitivity in transgenic Arabidopsis plants. Expression analysis indicates that LeETR4 accounts for most of the putative ethylene-receptor mRNA present in reproductive tissues, but, like LeETR5, it is less abundant in vegetative tissues. Taken together, ethylene perception in tomato is potentially quite complex, with at least five structurally divergent, putative receptor family members exhibiting significant variation in expression levels throughout development.     

Effect of salt and osmotic stress upon expression of the ethylene receptor ETR1 in Arabidopsis thaliana

In hormone perception, varying the concentrations of hormone, receptor, or downstream signaling elements can modulate signal transduction. Previous research has demonstrated that ethylene biosynthesis in plants is regulated by abiotic factors. Here we report that exposure of Arabidopsis plants to NaCl reduced expression of the ethylene receptor ETR1. The change in gene expression was reflected at the protein level based on immunoblot analysis. Further analysis supports a general effect of osmotic stress upon the expression level of ETR1. The reduction in ETR1 levels should cause increased sensitivity of the plant to ethylene. These results suggest that plant responses to abiotic stress are modulated by changes in the expression level of ethylene receptors.     

Control of ethylene-mediated processes in tomato at the level of receptors

The plant hormone ethylene controls many aspects of development and response to the environment. In tomato, ethylene is an essential component of flower senescence, organ abscission, adventitious root initiation, and fruit ripening. Responses to ethylene are also critical for aspects of biotic and abiotic stress responses. Clearly, much of the control of these events occurs at the level of hormone synthesis. However, it is becoming apparent that levels of the ethylene receptors are also highly regulated. The tomato ethylene receptors are encoded by a family of six genes. Levels of expression of these genes are spatially and temporally controlled throughout development. Further, a subset of the receptor genes respond to external stimuli. Genetic and biochemical evidence supports a model in which the ethylene receptors act as negative regulators of downstream responses; in the absence of ethylene, receptors actively suppress expression of ethylene responsive genes. Consistent with this model, a reduction in the overall level of receptor increases ethylene responsiveness of a tissue while higher expression of receptor decreases ethylene sensitivity. Evidence to support this model will be presented.     

The role of local biosynthesis of auxin and cytokinin in plant development

Plant hormones are tightly regulated in response to environmental and developmental signals. It has long been speculated that biosynthesis of hormones occurs broadly in plant organs and that intricate, spatiotemporal regulation of hormones in developing organ primordia is achieved through transport and signal perception. However, recent identification of genes crucial for biosynthesis of auxin and cytokinin reveals that localized hormone biosynthesis also plays an important role in organ growth and patterning.     

Antisense inhibition of the Nr gene restores normal ripening to the tomato Never-ripe mutant, consistent with the ethylene receptor-inhibition model

The hormone ethylene regulates many aspects of plant growth and development, including fruit ripening. In transgenic tomato (Lycopersicon esculentum) plants, antisense inhibition of ethylene biosynthetic genes results in inhibited or delayed ripening. The dominant tomato mutant, Never-ripe (Nr), is insensitive to ethylene and fruit fail to ripen. The Nr phenotype results from mutation of the ethylene receptor encoded by the NR gene, such that it can no longer bind the hormone. NR has homology to the Arabidopsis ethylene receptors. Studies on ethylene perception in Arabidopsis have demonstrated that receptors operate by a "receptor inhibition" mode of action, in which they actively repress ethylene responses in the absence of the hormone, and are inactive when bound to ethylene. In ripening tomato fruit, expression of NR is highly regulated, increasing in expression at the onset of ripening, coincident with increased ethylene production. This expression suggests a requirement for the NR gene product during the ripening process, and implies that ethylene signaling via the tomato NR receptor might not operate by receptor inhibition. We used antisense inhibition to investigate the role of NR in ripening tomato fruit and determine its mode of action. We demonstrate restoration of normal ripening in Nr fruit by inhibition of the mutant Nr gene, indicating that this receptor is not required for normal ripening, and confirming receptor inhibition as the mode of action of the NR protein.     

Involvement of ethylene biosynthesis and perception in the susceptibility of citrus fruits to Penicillium digitatum infection and the accumulation of defence-related mRNAs

Citrus fruits infected with the fungus Penicillium digitatum substantially increase the production of the plant hormone ethylene. In this study, the regulation of ethylene biosynthesis in Citrus sinensis-infected fruits and its putative involvement in an active defence response against P. digitatum infection is examined. Ethylene production is demonstrated as being the result of the co-ordinated and differential up-regulation of at least three ethylene biosynthetic genes: ACS1, ACS2, and ACO. Blocking ethylene perception by 1-MCP resulted in an increased ethylene production and ACS2 expression during infection and mechanical wounding, suggesting that this gene is negatively regulated by ethylene. ACO expression was induced by ethylene in the absence of wounding or infection, although further results indicate that its induction during the course of infection may not be primarily mediated by ethylene. Treatment with 1-MCP also increased susceptibility to Penicillium decay, showing an involvement of ethylene perception in promoting defence responses in citrus fruits. The changes in the expression of two defence-related genes up-regulated during infection were also studied: the ones coding for phenylalanine ammonia-lyase (PAL) and an acidic class II chitinase (ACR311). The onset of PAL expression after mechanical wounding or inoculation was not changed in 1-MCP-pretreated fruits, while its later increase during the course of infection was abolished. Chitinase gene induction was more related to mechanical damage and was partially repressed by ethylene. These studies indicate distinct possible regulatory mechanisms of plant fruit defence genes in the context of fungal infection and ethylene perception.     

Genetic mapping of ripening and ethylene-related loci in tomato

 The regulation of tomato fruit development and ripening is influenced by a large number of loci as demonstrated by the number of existing non-allelic fruit development mutations and a multitude of genes showing ripening-related expression patterns. Furthermore, analysis of transgenic and naturally occurring tomato mutants confirms the pivotal role of the gaseous hormone ethylene in the regulation of climacteric ripening. Here we report RFLP mapping of 32 independent tomato loci corresponding to genes known or hypothesized to influence fruit ripening and/or ethylene response. Mapped ethylene-response sequences fall into the categories of genes involved in either hormone biosynthesis or perception, while additional ripening-related genes include those involved in cell-wall metabolism and pigment biosynthesis. The placement of ripening and ethylene-response loci on the tomato RFLP map will facilitate both the identification and exclusion of candidate gene sequences corresponding to identified single gene and quantitative trait loci contributing to fruit development and ethylene response. Received: 26 October 1998 / Accepted: 13 November 1998     

Ethylene signalling is involved in regulation of phosphate starvation-induced gene expression and production of acid phosphatases and anthocyanin in Arabidopsis

? With the exception of root hair development, the role of the phytohormone ethylene is not clear in other aspects of plant responses to inorganic phosphate (Pi) starvation. ? The induction of AtPT2 was used as a marker to find novel signalling components involved in plant responses to Pi starvation. Using genetic and chemical approaches, we examined the role of ethylene in the regulation of plant responses to Pi starvation. ? hps2, an Arabidopsis mutant with enhanced sensitivity to Pi starvation, was identified and found to be a new allele of CTR1 that is a key negative regulator of ethylene responses. 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, increases plant sensitivity to Pi starvation, whereas the ethylene perception inhibitor Ag+ suppresses this response. The Pi starvation-induced gene expression and acid phosphatase activity are also enhanced in the hps2 mutant, but suppressed in the ethylene-insensitive mutant ein2-5. By contrast, we found that ethylene signalling plays a negative role in Pi starvation-induced anthocyanin production. ? These findings extend the roles of ethylene in the regulation of plant responses to Pi starvation and will help us to gain a better understanding of the molecular mechanism underlying these responses.     

番茄乙烯受体结构和功能研究进展

综述了近年来番茄乙烯受体研究方面的最新进展。以拟南芥的乙类受体为探针,从番茄加筛选得到Le-ETR1、Le-ETR2、Le-ETR3、Le-ETR4、Le-ETR55个有功能的乙烯受体基因。番茄乙类受体与细菌的双组分感受系统高度相似,同乙烯结合需要铜离子的协同作用。植物株发育期间通过激活某些受体基因的表达和（或）控制铜离子的转运调节乙烯敏感性。调节乙烯受体表达的基因工程显示了广阔的前景。但各个受体的功能及基因分析与活体标记的关系还需进一步研究。     

Top hits in contemporary JAZ: An update on jasmonate signaling

The phytohormone jasmonate (JA) regulates a wide range of growth, developmental, and defense-related processes during the plant life cycle. Identification of the JAZ family of proteins that repress JA responses has facilitated rapid progress in understanding how this lipid-derived hormone controls gene expression. Recent analysis of JAZ proteins has provided insight into the nature of the JA receptor, the chemical specificity of signal perception, and cross-talk between JA and other hormone response pathways. Functional diversification of JAZ proteins by alternative splicing, together with the ability of JAZ proteins to homo- and heterodimerize, provide mechanisms to enhance combinatorial diversity and versatility in gene regulation by JA.     

Ethylene in vegetative development: a tale with a riddle

The vegetative development of plants is strongly dependent on the action of phytohormones. For over a century, the effects of ethylene on plants have been studied, illustrating the profound impact of this gaseous hormone on plant growth, development and stress responses. Ethylene signaling is under tight self-control at various levels. Feedback regulation occurs on both biosynthesis and signaling. For its role in developmental processes, ethylene has a close and reciprocal relation with auxin, another major determinant of plant architecture. Here, we discuss, in view of novel findings mainly in the reference plant Arabidopsis, how ethylene is distributed and perceived throughout the plant at the organ, tissue and cellular levels, and reflect on how plants benefit from the complex interaction of ethylene and auxin, determining their shape. Furthermore, we elaborate on the implications of recent discoveries on the control of ethylene signaling.     

Role of ethylene receptors during senescence and ripening in horticultural crops

The past two decades have been rewarding in terms of deciphering the ethylene signal transduction and functional validation of the ethylene receptor and downstream genes involved in the cascade. Our knowledge of ethylene receptors and its signal transduction pathway provides us a robust platform where we can think of manipulating and regulating ethylene sensitivity by the use of genetic engineering and making transgenic. This review focuses on ethylene perception, receptor mediated regulation of ethylene biosynthesis, role of ethylene receptors in flower senescence, fruit ripening and other effects induced by ethylene. The expression behavior of the receptor and downstream molecules in climacteric and non climacteric crops is also elaborated upon. Possible strategies and recent advances in altering the ethylene sensitivity of plants using ethylene receptor genes in an attempt to modulate the regulation and sensitivity to ethylene have also been discussed. Not only will these transgenic plants be a boon to post-harvest physiology and crop improvement but, it will also help us in discovering the mechanism of regulation of ethylene sensitivity.     

Cooperative ethylene receptor signaling

The gaseous plant hormone ethylene is perceived by a family of five ethylene receptor members in the dicotyledonous model plant Arabidopsis. Genetic and biochemical studies suggest that the ethylene response is suppressed by ethylene receptor complexes, but the biochemical nature of the receptor signal is unknown. Without appropriate biochemical measures to trace the ethylene receptor signal and quantify the signal strength, the biological significance of the modulation of ethylene responses by multiple ethylene receptors has yet to be fully addressed. Nevertheless, the ethylene receptor signal strength can be reflected by degrees in alteration of various ethylene response phenotypes and in expression levels of ethylene-inducible genes. This mini-review highlights studies that have advanced our understanding of cooperative ethylene receptor signaling.     

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。     

Molecular analysis of early rice stamen development using organ-specific gene expression profiling

Elucidating the regulatory mechanisms of plant organ formation is an important component of plant developmental biology and will be useful for crop improvement applications. Plant organ formation, or organogenesis, occurs when a group of primordial cells differentiates into an organ, through a well-orchestrated series of events, with a given shape, structure and function. Research over the past two decades has elucidated the molecular mechanisms of organ identity and dorsalventral axis determinations. However, little is known about the molecular mechanisms underlying the successive processes. To develop an effective approach for studying organ formation at the molecular level, we generated organ-specific gene expression profiles (GEPs) reflecting early development in rice stamen. In this study, we demonstrated that the GEPs are highly correlated with early stamen development, suggesting that this analysis is useful for dissecting stamen development regulation. Based on the molecular and morphological correlation, we found that over 26 genes, that were preferentially up-regulated during early stamen development, may participate in stamen development regulation. In addition, we found that differentially expressed genes during early stamen development are clustered into two clades, suggesting that stamen development may comprise of two distinct phases of pattern formation and cellular differentiation. Moreover, the organ-specific quantitative changes in gene expression levels may play a critical role for regulating plant organ formation. Electronic Supplementary Material Supplementary material is available for this article at Xiao-Chun Lu, Hua-Qin Gong contributed equally to this work.