Signal convergence through the lenses of MAP kinases: paradigms of stress and hormone signaling in plants

Common mechanisms plants use to translate the external stimuli into cellular responses are the activation of mitogen-activated protein kinase (MAPK) cascade. These MAPK cascades are highly conserved in eukaryotes and consist of three subsequently acting protein kinases, MAP kinase kinase kinase (MAPKKK), MAP kinase kinase (MAPKK) and MAP kinase (MAPK) which are linked in various ways with upstream receptors and downstream targets. Plant MAPK cascades regulate numerous processes, including various environmental stresses, hormones, cell division and developmental processes. The number of MAPKKs in Arabidopsis and rice is almost half the number of MAPKs pointing important role of MAPKKs in integrating signals from several MAPKKKs and transducing signals to various MAPKs. The cross talks between different signal transduction pathways are concentrated at the level of MAPKK in the MAPK cascade. Here we discussed the insights into MAPKK mediated response to environmental stresses and in plant growth and development.     

Mitogen-activated protein kinase signaling in plants under abiotic stress

Mitogen-activated protein kinase cascade is evolutionarily conserved signal transduction module involved in transducing extracellular signals to the nucleus for appropriate cellular adjustment. This cascade consists essentially of three components, a MAPK kinase kinase (MAPKKK), a MAPK kinase (MAPKK) and a MAPK connected to each other by the event of phosphorylation. These kinases play various roles in intra- and extra-cellular signaling in plants by transferring the information from sensors to responses. Signaling through MAP kinase cascade can lead to cellular responses including cell division, differentiation as well as responses to various stresses. MAPK signaling has also been associated with hormonal responses. In plants, MAP kinases are represented by multigene families and are involved in efficient transmission of specific stimuli and also involved in the regulation of the antioxidant defense system in response to stress signaling. In the current review we summarize and investigate the participation of MAPKs as possible mediators of various abiotic stresses in plants.Key words: abiotic stress, cross talk, mitogen-activated protein kinases, heat map, MAPK signaling, signal transduction, stress signaling     

植物MAP激酶级联途径研究进展

MAP激酶(促分裂原活化蛋白激酶)级联途径可以将不同的细胞膜感受器与细胞应答联系起来,响应各种生物以及非生物胁迫,在植物激素信号以及细胞分裂和发育过程中发挥着重要的作用.为有效地传递各种特异信号,MAP激酶级联相互交叉形成复杂的信号传递网络.近年来,随着功能获得型突变体、功能缺失型突变体的获得以及其它一些新技术的应用,进一步阐明了MAP激酶级联途径在信号传导过程中的功能和作用.本文主要对植物MAPK级联途径在信号传导过程中交叉串通以及复杂性的最新研究结果进行综述.     

植物丝裂原活化蛋白激酶级联信号转导通路研究进展

丝裂原活化蛋白激酶(MAPK)是酵母、动物和植物等真核生物中普遍存在和高度保守的一类信号转导通路,由MAPKKK、MAPKK和MAPK等3部分组成,在应对生物非生物胁迫、激素、细胞分裂调控及植物生长发育等过程中发挥重要作用。该文对近年来国内外有关MAPK级联通路的组成、在植株体内的生物学功能以及MAPK通路的失活进行了概述,旨在为今后MAPK通路介导的信号转导机制的研究提供参考依据。     

环境胁迫下植物MAPK多叠级联响应(英文)

Plant mitogen-activated protein kinases(MAPKs) are involved in growth,evelopment and responses to endogenous and environmental cues．which link stimuli that areactivated by external sensors to cellular responses．In Arabidopsis,as amodel,all of MAP kinase genes have been listed and classified．Based on the Arabidopsis MAPK families．a number of MAPk inase genes in other plant species have been recently isolated and classified．Most of the cloned MAPk inase genes can be activated by avariety of stresss timuli including pathogen infection．wounding．temperature,drought．salinity．osmolarity．UV irradiation．ozone and reactive oxygen species．Some tools and strategies are used to investigate their functions and signal pathways under different environmental stresses．indicating complexity and crosstalk of plant MAPk inase signaling pathways．It is still necessary to explore more novel tools and strategies to clarify MAPK signaling pathways,and how to apply the MAPK cascade to improve the resistance of crop to abiotic and biotic stress     

拟南芥AtMPK6的信号转导功能和参与发育调控的研究进展

促分裂原活化蛋白激酶（MAPK）级联途径主要MAPKKK、MAPKK和MAPK三个组分构成,彼此逐级磷酸化进而传递细胞信号。这些激酶可以将信息从感应器传递到效应器,并在胞内外信号传递中起多种作用。同时,MAPK级联途径通过相互“交谈”形成复杂的信号传递网络,从而有效地传递各种特异信号。迄今为止,拟南芥AtMPK3、AtMPK4和AtMPK6是研究最多的MAPKs。本文综述AtMPK6参与调控植物对逆境胁迫的响应,以及在生长发育过程中的作用,并介绍AtMPK6与蛋白磷酸酶之间的关系。     

Redox signaling and the MAP kinase pathways

The mitogen-activated protein (MAP) kinases are a large family of proline-directed, serine/threonine kinases that require tyrosine and threonine phosphorylation of a TxY motif in the activation loop for activation through a phosphorylation cascade involving a MAPKKK, MAPKK and MAPK, often referred to as the MAP kinase module. Three separate such modules have been identified, based on the TxY motif of the MAP kinase and the dual-specificity kinases that strictly phosphorylate their specific TxY sequence. They are the extracellular signal regulated kinases (ERKs), c-jun N-terminal kinases (JNKs) and p38 MAPKs. The ERKs are mainly associated with proliferation and differentiation while the JNKs and p38MAP kinases regulate responses to cellular stresses. Redox homeostasis is critical for proper cellular function. While reactive oxygen species (ROS) and oxidative stress have been implicated in injury, a rapidly growing literature suggests that a transient increase in ROS levels is an important mediator of proliferation and results in activation of various signaling molecules and pathways, among which the MAP kinases. This review will summarize the role of ROS in MAP kinase activation in various systems, including in macrophages, cells of myeloid origin that play an essential role in inflammation and express a multi-component NADPH oxidase that catalyzes the receptor-regulated production of ROS.     

Modeling of the MAPK machinery activation in response to various abiotic and biotic stresses in plants by a system biology approach

Mitogen-Activated Protein Kinases (MAPKs) cascade plays an important role in regulating plant growth and development, generating cellular responses to the extracellular stimuli. MAPKs cascade mainly consist of three sub-families i.e. mitogen-activated protein kinase kinase kinase (MAPKKK), mitogen-activated protein kinase kinase (MAPKK) and mitogen activated protein kinase (MAPK), several cascades of which are activated by various abiotic and biotic stresses. In this work we have modeled the holistic molecular mechanisms essential to MAPKs activation in response to several abiotic and biotic stresses through a system biology approach and performed its simulation studies. As extent of abiotic and biotic stresses goes on increasing, the process of cell division, cell growth and cell differentiation slow down in time dependent manner. The models developed depict the combinatorial and multicomponent signaling triggered in response to several abiotic and biotic factors. These models can be used to predict behavior of cells in event of various stresses depending on their time and exposure through activation of complex signaling cascades.     

环境胁迫下植物MAPK多叠级联响应

植物MAP(mitogen-activated protein)激酶涉及植物的生长发育、对内源和外界环境刺激的反应.MAP激酶能将胞外感受器引起的刺激传递到胞内引起细胞的反应.拟南芥(Arabidopsis thaliana)作为模式植物,其全部的MAP激酶已经列出并进行了分类.根据已分类的拟南芥MAP激酶家族,已经分离出大量的MAP激酶基因,并将它们进行分类,发现它们大多能被包括病原、创伤、温度、干旱、盐、渗透、紫外线辐射、臭氧和活性氧等胁迫刺激激活.通过研究在不同环境胁迫下的功能和信号路径,发现植物MAP激酶信号传递系统是复杂且相互交错的.需要开发一些新的工具和策略去阐明MAPK信号传递路径,以及如何利用MAPK系统去改善农作物对生物和非生物胁迫的抗性.     

植物MAPK信号转导组分的细胞定位与选择性剪接

促分裂原活化蛋白激酶(MAPK)级联途径在真核生物中是高度保守的,由MAPKs,MAPKKs,MAPKKKs组成,通过MAPKKK→MAPKK→MAPK逐级磷酸化传递细胞信号.已有大量研究表明,MAPK在植物响应生物与非生物胁迫,以及植物激素和细胞周期的信号转导中起重要作用.在植物响应各种逆境过程中激活的MAPK基因,细胞内的定位发生动态变化.选择性剪接是真核生物中调节基因表达的重要模式,能够影响蛋白的结合特性、胞内定位、酶的活性、蛋白的稳定性和翻译后的修饰.MAPK基因的选择性剪接能产生不同的转录异型并具有不同的亚细胞定位.本文综述这方面的研究进展.     

MAPK信号通路在辐射应答中的作用

丝裂原活化蛋白激酶（MAPK）超家族是介导细胞反应的重要信号系统,主要由MAPK、MAPK激酶（MAPKK）、MAPKK激酶（MAPKKK）等3类保守的蛋白激酶组成,通过级联反应不断磷酸化下游靶蛋白而参与细胞的增殖、分化、衰老、凋亡。辐射损伤使细胞膜受体和其他感应分子激活细胞内的MAPK信号通路,产生一系列应答反应。简要介绍MAPK家族中各条通路在辐射应答中的作用。     

Deciphering the MAP kinase pathway

MAP kinases (MAPK) are serine/threonine kinases which are activated by a dual phosphorylation on threonine and tyrosine residues. Their specific upstream activators, called MAP kinase kinases (MAPKK), constitute a new family of dual-specific threonine/tyrosine kinases, which in turn are activated by upstream MAP kinase kinase kinases (MAPKKK). These three kinase families are successively stimulated in a cascade of activation described in various species such as mammals, frog, fly, worm or yeast.In mammals, the MAP kinase module lies on the signaling pathway triggered by numerous agonists such as growth factors, hormones, lymphokines, tumor promoters, stress factors, etc. Targets of MAP kinase have been characterize tin all subcellular compartments. In yeast, genetic epistasis helped to characterize the presence of several MAP kinase modules in the same system. By complementation tests, the relationships existing between phylogenetically distant members of each kinase family have been described. The roles of the MAP kinase cascade have been analyzed by engineering various mutations in the kinases of the module. The MAP kinase cascade has thus been implicated in higher eukaryotes in cell growth, cell fate and differentiation, and in low eukaryotes, in conjugation, osmotic stress, cell wall constrct and mitosis.     

Conserved docking site is essential for activation of mammalian MAP kinase kinases by specific MAP kinase kinase kinases

Mammalian mitogen-activated protein kinase (MAPK) cascades control various cellular events, ranging from cell growth to apoptosis, in response to external stimuli. A conserved docking site, termed DVD, is found in the mammalian MAP kinase kinases (MAPKKs) belonging to the three major subfamilies, namely MEK1, MKK4/7, and MKK3/6. The DVD sites bind to their specific upstream MAP kinase kinase kinases (MAPKKKs), including MTK1 (MEKK4), ASK1, TAK1, TAO2, MEKK1, and Raf-1. DVD site is a stretch of about 20 amino acids immediately on the C-terminal side of the MAPKK catalytic domain. Mutations in the DVD site strongly inhibited MAPKKs from binding to, and being activated by, their specific MAPKKKs, both in vitro and in vivo. DVD site mutants could not be activated by various external stimuli in vivo. Synthetic DVD oligopeptides inhibited specific MAPKK activation, both in vitro and in vivo, demonstrating the critical importance of the DVD docking in MAPK signaling.     

OMTK1, a novel MAPKKK, channels oxidative stress signaling through direct MAPK interaction

In common with other eukaryotes, plants utilize mitogen-activated protein kinase (MAPK) cascades to mediate responses to a wide variety of stimuli. In contrast to other eukaryotes, plants have an unusually large number of MAPK components, such as more than 20 MAPKs, 10 MAPK kinases (MAPKKs), and 60 MAPKK kinases (MAPKKKs) in Arabidopsis (MAPK Group (2002) Trends Plant Sci. 7, 301-308). Presently it is mostly unknown how MAPK signaling specificity is generated in plants. Here we have isolated OMTK1 (oxidative stress-activated MAP triple-kinase 1), a novel MAPKKK from alfalfa (Medicago sativa). In plant protoplasts, OMTK1 showed basal kinase activity and was found to induce cell death. Among a panel of hormones and stresses tested, only H(2)O(2) was found to activate OMTK1. Out of four MAPKs, OMTK1 specifically activated MMK3 resulting in an increased cell death rate. Pull-down analysis between recombinant proteins indicated that OMTK1 directly interacts with MMK3 and that OMTK1 and MMK3 are part of a protein complex in vivo. These results indicate that OMTK1 plays a MAPK scaffolding role and functions in activation of H(2)O(2) -induced cell death in plants.     

Diverse signals converge at MAPK cascades in plant.

Mitogen-activated protein kinases (MAPKs) are important signal transducing enzymes that connects diverse receptors/sensors to a wide range of cellular responses in mammals, yeasts and plants. In recent years, a large number of different components of plant MAPK cascades were isolated. Molecular and biochemical studies have revealed that plant MAPKs play important role in the response to a broad variety of biotic and abiotic stresses, including wounding, pathogen infection, temperature, drought, salinity, but also in the signaling of plant hormones and the cell division. This review briefly summaries the recent research results about the cross-talk and complexity of MAP kinase cascades in plant obtained from functional analyses.     

Mitogen-activated protein kinase cascades in plants: a new nomenclature

Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes, including yeasts, animals and plants. These protein phosphorylation cascades link extracellular stimuli to a wide range of cellular responses. In plants, MAPK cascades are involved in responses to various biotic and abiotic stresses, hormones, cell division and developmental processes. Completion of the Arabidopsis genome-sequencing project has revealed the existence of 20 MAPKs, 10 MAPK kinases and 60 MAPK kinase kinases. Here, we propose a simplified nomenclature for Arabidopsis MAPKs and MAPK kinases that might also serve as a basis for standard annotation of these gene families in all plants.