A comparative genomic analysis of plant hormone related genes in different species

Plant hormones are small molecules that play important roles throughout the life span of a plant,known as auxin,gibberellin,cyto-kinin,abscisic acid,ethylene,jasmonic acid,salicylic acid,and brassinosteroid.Genetic and molecular studies in the model organism Arabidopsis thaliana have revealed the individual pathways of various plant hormone responses.In this study,we selected 479 genes that were convincingly associated with various hormone actions based on genetic evidence.By using these 479 genes as querie...     

Ethylene in mutualistic symbioses

Ethylene (ET) is a gaseous phytohormone that participates in various plant physiological processes and essentially contributes to plant immunity. ET conducts its functions by regulating the expression of ET-responsive genes or in crosstalk with other hormones. Several recent studies have shown the significance of ET in the establishment and development of plant-microbe interactions. Therefore, it is not surprising that pathogens and mutualistic symbionts target ET synthesis or signaling to colonize plants. This review introduces the significance of ET metabolism in plant-microbe interactions, with an emphasis on its role in mutualistic symbioses.     

Brassinosteroid signal transduction--choices of signals and receptors

Small signaling molecules that mediate cell-cell communication are essential for developmental regulation in multicellular organisms. Among them are the steroids and peptide hormones that regulate growth in both plants and animals. In plants, brassinosteroids (BRs) are perceived by the cell surface receptor kinase BRI1, which is distinct from the animal steroid receptors. Identification of components of the BR signaling pathway has revealed similarities to other animal and plant signal transduction pathways. Recent studies demonstrated that tomato BRI1 (tBRI1) perceives both BR and the peptide hormone systemin, raising new questions about the molecular mechanism and evolution of receptor-ligand specificity.     

Ligand–receptor interactions in plant hormone signaling

Small-molecule plant hormones principally control plant growth, development, differentiation, and environmental responses. Nine types of plant hormones are ubiquitous in angiosperms, and the molecular mechanisms of their hormone actions have been elucidated during the last two decades by genomic decoding of model plants with genetic mutants. In particular, the discovery of hormone receptors has greatly contributed to the understanding of signal transduction systems. The three-dimensional structure of the ligand–receptor complex has been determined for eight of the nine hormones by X-ray crystal structure analysis, and ligand perception mechanisms have been revealed at the atomic level. Collective research has revealed the molecular function of plant hormones that act as either molecular glue or an allosteric regulator for activation of receptors. In this review, we present an overview of the respective hormone signal transduction and describe the structural bases of ligand–receptor interactions.     

The divergence and positive selection of the plant‐specific BURP‐containing protein family

BURP domain‐containing proteins belong to a plant‐specific protein family and have diverse roles in plant development and stress responses. However, our understanding about the genetic divergence patterns and evolutionary rates of these proteins remain inadequate. In this study, 15 plant genomes were explored to elucidate the genetic origins, divergence, and functions of these proteins. One hundred and twenty‐five BURP protein‐encoding genes were identified from four main plant lineages, including 13 higher plant species. The absence of BURP family genes in unicellular and multicellular algae suggests that this family (1) appeared when plants shifted from relatively stable aquatic environments to land, where conditions are more variable and stressful, and (2) is critical in the adaptation of plants to adverse environments. Promoter analysis revealed that several responsive elements to plant hormones and external environment stresses are concentrated in the promoter region of BURP protein‐encoding genes. This finding confirms that these genes influence plant stress responses. Several segmentally and tandem‐duplicated gene pairs were identified from eight plant species. Thus, in general, BURP domain‐containing genes have been subject to strong positive selection, even though these genes have conformed to different expansion models in different species. Our study also detected certain critical amino acid sites that may have contributed to functional divergence among groups or subgroups. Unexpectedly, all of the critical amino acid residues of functional divergence and positive selection were exclusively located in the C‐terminal region of the BURP domain. In conclusion, our results contribute novel insights into the genetic divergence patterns and evolutionary rates of BURP proteins.     

Novel approaches for the study of vertebrate steroid hormone receptors

Steroid hormones are essential for the normal function of most organ systems in vertebrates. Reproductive activities in females and males, such as the differentiation, growth and maintenance of the reproductive system, require signaling by sex steroid hormones. Although extensively studied in mammals and a few fish and bird species, the evolution and molecular mechanisms associated with the nuclear steroid hormone receptors are still poorly understood in amphibians and reptiles. Given our interest in environmental signaling of sex determination as well as a major interest in environmental contaminants that can mimic steroid hormone signaling, we have established an approach to study the molecular function (ligand binding and trans-activation) of steroid hormone receptors cloned from reptiles. This approach involves molecular cloning and sequencing of steroid hormone receptors, phylogenic analysis and in vitro trans-activation assays using endogenous or exogenous ligands. Comparing the in vitro trans-activation induced by different ligands with receptors cloned from different species would develop additional functional relationships (classification) among steroid hormone receptors. This approach can provide insight into understanding why each species could have different responses to exogenous ligands. Further, we have developed a novel and less invasive approach to obtaining mRNA for molecular cloning and sequencing of steroid hormone receptors in reptiles and other non-mammalian species, using blood cells as a source of genetic material. For example, white blood cells (WBCs) and red blood cells (RBCs) of the American alligator both express steroid hormone receptors and have adequate amounts of mRNA for molecular cloning. This approach would allow us to analyze components of endocrine function of steroid hormones without sacrificing animals. Especially in endangered species, this approach could provide an understanding of endocrine functions, elucidate the phylogenic relationships of various receptors in vitro, such as the steroid hormone receptors, and determine possible effects of environmental contaminants in a minimally invasive manner.     

Two-component elements mediate interactions between cytokinin and salicylic acid in plant immunity

Recent studies have revealed an important role for hormones in plant immunity. We are now beginning to understand the contribution of crosstalk among different hormone signaling networks to the outcome of plant-pathogen interactions. Cytokinins are plant hormones that regulate development and responses to the environment. Cytokinin signaling involves a phosphorelay circuitry similar to two-component systems used by bacteria and fungi to perceive and react to various environmental stimuli. In this study, we asked whether cytokinin and components of cytokinin signaling contribute to plant immunity. We demonstrate that cytokinin levels in Arabidopsis are important in determining the amplitude of immune responses, ultimately influencing the outcome of plant-pathogen interactions. We show that high concentrations of cytokinin lead to increased defense responses to a virulent oomycete pathogen, through a process that is dependent on salicylic acid (SA) accumulation and activation of defense gene expression. Surprisingly, treatment with lower concentrations of cytokinin results in increased susceptibility. These functions for cytokinin in plant immunity require a host phosphorelay system and are mediated in part by type-A response regulators, which act as negative regulators of basal and pathogen-induced SA-dependent gene expression. Our results support a model in which cytokinin up-regulates plant immunity via an elevation of SA-dependent defense responses and in which SA in turn feedback-inhibits cytokinin signaling. The crosstalk between cytokinin and SA signaling networks may help plants fine-tune defense responses against pathogens.     

茶树诱导抗虫性的研究进展

为了抵御植食性昆虫的为害,植物在进化过程中形成了包括组成抗性和诱导抗性在内的复杂防御体系.在通过受体识别茶树害虫为害后,茶树会启动早期信号事件,继而激活茉莉酸、水杨酸、乙烯和赤霉素等植物激素信号通路,从而引起次生代谢物的积累,最终对害虫产生直接和间接抗性.基于近年来茶树害虫为害诱导的茶树防御反应及其相关调控机理的研究进...