Plant MAP kinase pathways: how many and what for?

Mitogen activated protein kinases (MAPK) are important mediators in signal transmission, connecting the perception of external stimuli to cellular responses. MAPK cascades are involved in signalling various biotic and abiotic stresses, like wounding and pathogen infection, temperature stress or drought, but also some plant hormones, such as ethylene and auxin. Moreover, MAPKs have been implicated in cell cycle and developmental processes. In Arabidopsis mutant screens and in vivo assays several components of plant MAPK cascades have been identified. This review compares results obtained from functional analyses of MAPK cascades in plants with recent data obtained from searching the complete Arabidopsis genome. This analysis reveals that plants have an overall of 24 MAPK pathways of which only a small subset has been studied so far.     

Emerging MAP kinase pathways in plant stress signalling

Mitogen-activated protein kinase (MAPK) pathways transfer information from sensors to cellular responses in all eukaryotes. A surprisingly large number of genes encoding MAPK pathway components have been uncovered by analysing model plant genomes, suggesting that MAPK cascades are abundant players of signal transduction. Recent investigations have confirmed major roles of defined MAPK pathways in development, cell proliferation and hormone physiology, as well as in biotic and abiotic stress signalling. Latest insights and findings are discussed in the context of novel MAPK pathways in plant stress signalling.     

Roles of mitogen-activated protein kinase cascades in ABA signaling

Abscisic acid (ABA) is a universal hormone in higher plants and plays a major role in various aspects of plant stress, growth, and development. Mitogen-activated protein kinase (MAPK) cascades are key signaling modules for responding to various extracellular stimuli in plants. The available data suggest that MAPK cascades are involved in some ABA responses, including antioxidant defense, guard cell signaling, and seed germination. Some MAPK phosphatases have also been demonstrated to be implicated in ABA responses. The goal of this review is to piece together the findings concerning MAPK cascades in ABA signaling. Questions and further perspectives of the roles played by MAPK cascades in ABA signaling are also furnished.     

Rice MAPKs

Mitogen-activated protein kinase (MAPK) cascades are evolutionary conserved from unicellular to complex eukaryotic organisms, and constitute one of the major signalling pathways involved in regulating a wide range of cellular activities from growth and development to cell death. MAPKs of rice (Oryza sativa L.), the most important of all food crops and an established monocot plant research model, have seen considerable progress mainly on their identification and characterization during the past one year alone. These studies have provided new information on the response and regulation of rice MAPKs, in particular on their possible role/function in the rice self-defense pathways. It is believed that further work on MAPK cascades in rice will widen our understanding of the MAPK signalling pathways, and may lead to the establishment of a biological model on this critical early signalling event in monocots. In this review, we bring together all the recent developments in rice MAPKs and discuss their significance and future direction in light of the present data and the progress made in dicot model plants.     

植物MAPK级联途径参与调控ABA信号转导

促分裂原活化蛋白激酶(MAPK)级联途径信号通路在真核生物细胞信号的转换和放大过程中起重要作用。MAPK级联途径由三个成员组成,分别是MAPK、MAPKK及MAPKKK,此三个信号组分按照MAPKKK-MAPKK-MAPK的方式依次磷酸化将外源信号级联放大向下传递。大量研究表明,植物MAPK级联途径参与调控脱落酸(ABA)信号转导。因此,该文就ABA和MAPK的生物学功能、ABA信号转导中的磷酸化与去磷酸化以及MAPK级联途径与ABA信号转导之间的关系等方面的研究进展进行综述,以便进一步认识MAPK和ABA信号转导的分子机制。     

植物中的MAPK及其在信号传导中的作用

促分裂原活化蛋白激酶(MAPKs)是一类存在于真核生物中的丝氨酸/苏氨酸蛋白激酶。同动物和酵母中MAPKs类似,植物中的MAPK级联途径也是由MAPKs、MAPKKs、MAPKKKs三种类型的激酶组成。植物细胞内受体接受外界刺激信号,然后依次磷酸化激活MAPKKKs、MAPKKs和MAPKs,并影响相关基因表达。目前已经从植物中分离到一些MAPKs、MAPKKs和MAPKKKs,它们参与了植物激素、生物胁迫及非生物胁迫等过程的信号传导。介绍了植物响应外界环境胁迫过程中,不同机制和因子对MAPKs级联途径的调控。     

MAPK级联途径参与ABA信号转导调节的植物生长发育过程

植物激素ABA参与调控植物生长发育和生理代谢以及多种胁迫应答过程,促分裂原活化蛋白激酶（MAPK）级联途径应答于多种生物和非生物胁迫,广泛参与调控植物的生长发育。MAPK级联途径与ABA信号转导协同作用参与调控植物种子萌发、气孔运动和生长发育,本文主要归纳了植物中受ABA调控激活的MAPK级联途径成员,阐述了它们参与ABA信号转导调控植物生理反应和生长发育的过程,并对MAPK级联途径与ABA信号转导的研究方向作出了展望,指出对MAPK下游底物的筛选是完善MAPK级联途径的重要组成部分。     

From signal to cell polarity: mitogen-activated protein kinases as sensors and effectors of cytoskeleton dynamicity

Mitogen-activated protein kinases (MAPKs) are ubiquitous phosphorylation enzymes involved in signal transduction, gene expression and activation of diverse cytoskeletal proteins. MAPKs participate in the regulation of a broad range of crucial cellular processes including cell survival, division, polarization, stress responses, and metabolism. Phosphorylation of cytoskeletal proteins usually results in the rearrangement of cytoskeletal arrays leading to morphological changes and cell polarization. On the other hand, some cytoskeletal motor proteins, such as kinesins, could activate MAPK members and participate in signal delivery to the proper cellular destination (e.g. during cell division). Moreover, changes in the integrity of cytoskeletal elements have direct impacts on MAPK activity. Recent evidence suggests that there is bi-directional signalling between MAPK cascades and cytoskeleton. The focus here is on this cross-talk between MAPK signalling and the cytoskeleton in various eukaryotic systems including yeast, plants, and mammals and a role is proposed for MAPKs as sensors monitoring the cytoskeleton-dependent balance of forces within the cell.     

AtMPK4 is required for male-specific meiotic cytokinesis in Arabidopsis

Mitogen-activated protein kinase (MAPK) cascades have been implicated in regulating various aspects of plant development, including somatic cytokinesis. The evolution of expanded plant MAPK gene families has enabled the diversification of potential MAPK cascades, but functionally overlapping components are also well documented. Here we report that Arabidopsis MPK4, an MAPK that was previously described as a regulator of disease resistance, can interact with and be phosphorylated by the cytokinesis-related MAP kinase kinase, AtMKK6. In mpk4 mutant plants, anthers can develop normal microspore mother cells (MMCs) and peripheral supporting tissues, but the MMCs fail to form a normal intersporal callose wall after male meiosis, and thus cannot complete meiotic cytokinesis. Nevertheless, the multinucleate mpk4 microspores subsequently proceed through mitotic cytokinesis, resulting in enlarged mature pollen grains that possess increased sets of the tricellular structure. This pollen development phenotype is reminiscent of those observed in both atnack2/tes/stud and anq1/mkk6 mutants, and protein-protein interaction analysis defines a putative signalling module linking AtNACK2/TES/STUD, AtANP3, AtMKK6 and AtMPK4 together as a cascade that facilitates male-specific meiotic cytokinesis in Arabidopsis.     

Involvement of Potato (Solanum tuberosum L.) MKK6 in Response to Potato virus Y

Mitogen-activated protein kinase (MAPK) cascades have crucial roles in the regulation of plant development and in plant responses to stress. Plant recognition of pathogen-associated molecular patterns or pathogen-derived effector proteins has been shown to trigger activation of several MAPKs. This then controls defence responses, including synthesis and/or signalling of defence hormones and activation of defence related genes. The MAPK cascade genes are highly complex and interconnected, and thus the precise signalling mechanisms in specific plant–pathogen interactions are still not known. Here we investigated the MAPK signalling network involved in immune responses of potato (Solanum tuberosum L.) to Potato virus Y, an important potato pathogen worldwide. Sequence analysis was performed to identify the complete MAPK kinase (MKK) family in potato, and to identify those regulated in the hypersensitive resistance response to Potato virus Y infection. Arabidopsis has 10 MKK family members, of which we identified five in potato and tomato (Solanum lycopersicum L.), and eight in Nicotiana benthamiana. Among these, StMKK6 is the most strongly regulated gene in response to Potato virus Y. The salicylic acid treatment revealed that StMKK6 is regulated by the hormone that is in agreement with the salicylic acid-regulated domains found in the StMKK6 promoter. The involvement of StMKK6 in potato defence response was confirmed by localisation studies, where StMKK6 accumulated strongly only in Potato-virus-Y-infected plants, and predominantly in the cell nucleus. Using a yeast two-hybrid method, we identified three StMKK6 targets downstream in the MAPK cascade: StMAPK4_2, StMAPK6 and StMAPK13. These data together provide further insight into the StMKK6 signalling module and its involvement in plant defence.     

The role of radical burst via MAPK signaling in plant immunity

Plants rely on the innate immune system to defend themselves from pathogen attacks. Reactive oxygen species (ROS) and nitric oxide (NO) play key roles in the activation of disease resistance mechanisms in plants. The evolutionarily conserved mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes and have been implicated in the plant innate immunity. There have been many disputations about the relationship between the radicals (ROS and NO) and MAPK cascades. Recently, we found that MAPK cascades participate in the regulation of the radical burst. Here, we discuss the regulatory mechanisms of the oxidative and NO bursts in response to pathogen attacks, and crosstalk between MAPK signaling and the radical burst.Key words: oxidative burst, MAPK, NADPH oxidase, NO burst, plant immunity     

A MAP kinase cascade that controls plant cytokinesis

Several components of mitogen-activated protein kinase (MAPK) cascades have been identified in higher plants and have been implicated in cellular responses to a wide variety of abiotic and biotic stimuli. Our recent work has demonstrated that a MAP kinase cascade is involved in the regulation of cytokinesis in plant cells. The MAP kinase cascade in tobacco includes NPK1 MAPK kinase kinase, NQK1 MAPK kinase, and NRK1 MAPK, and its activation is triggered by the binding of NACK1/2 kinesin-like protein to the NPK1 MAPK kinase kinase at the late M-phase of the cell cycle. We refer to this cascade as the NACK-PQR pathway. In this review, we introduce a mechanism for the regulation of plant cytokinesis, focusing on the role of the NACK-PQR pathway.     

真核生物的MAPK级联信号传递途径

MAPK级联途径在真核生物细胞的信号传递过程中起着重要的作用.MAPK级联途径由MAPK、MAPKK和MAPKKK三类酶蛋白组成.这三类蛋白质的结构非常保守,通过磷酸化作用传递各种信号.在酵母和动、植物细胞中已经发现了一系列的MAPK级联途径成员,使真核生物的信号传递途径逐渐得到阐明.     

植物信号传导中的磷脂酶

20世纪 80年代早期人们意识到构成细胞膜的磷脂不只是一道将细胞物质与外界隔开的屏障,而且是细胞对外界环境刺激作出应答的物质基础。磷脂酰肌醇（ｐｈｏｓｐｈｏｔｉｄｙｌｉｎｏｓｉｔｏｌ,ＰＩ）不但是构成细胞膜的重要组分（约占细胞膜组分的 10 %）,在细胞内外环境信号的传递方面也起着重要的作用［1］。磷脂酶（ｐｈｏｓｐｈｏｌｉｐａｓｅ）水解磷脂后产生的三磷酸肌醇 （ｉｎｏｓ ｉｔｏｌｔｒｉｓｐｈｏｓｐｈａｔｅ,ＩＰ3 ）／二酰基甘油（ｄｉａｃｙｌｇｌｙｃｅｒｏｌ,ＤＡＧ）、磷脂酸（ｐｈｏｓｐｈａｔｉｄｉｃａｃｉ…     

Genome-Wide Identification and Analysis of Expression Profiles of Maize Mitogen-Activated Protein Kinase Kinase Kinase

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction model in animals, yeast and plants. Plant MAPK cascades have been implicated in development and stress responses. Although MAPKKKs have been investigated in several plant species including Arabidopsis and rice, no systematic analysis has been conducted in maize. In this study, we performed a bioinformatics analysis of the entire maize genome and identified 74 MAPKKK genes. Phylogenetic analyses of MAPKKKs from maize, rice and Arabidopsis have classified them into three subgroups, which included Raf, ZIK and MEKK. Evolutionary relationships within subfamilies were also supported by exon-intron organizations and the conserved protein motifs. Further expression analysis of the MAPKKKs in microarray databases revealed that MAPKKKs were involved in important signaling pathways in maize different organs and developmental stages. Our genomics analysis of maize MAPKKK genes provides important information for evolutionary and functional characterization of this family in maize.     

Wound signalling in plants

Plants undergoing the onslaught of wound-causing agents activate mechanisms directed to healing and further defence. Responses to mechanical damage are either local or systemic or both and hence involve the generation, translocation, perception, and transduction of wound signals to activate the expression of wound-inducible genes. Although the central role for jasmonic acid in plant responses to wounding is well established, other compounds, including the oligopeptide systemin, oligosaccharides, and other phytohormones such as abscisic acid and ethylene, as well as physical factors such as hydraulic pressure or electrical pulses, have also been proposed to play a role in wound signalling. Different jasmonic acid-dependent and -independent wound signal transduction pathways have been identified recently and partially characterized. Components of these signalling pathways are mostly similar to those implicated in other signalling cascades in eukaryotes, and include reversible protein phosphorylation steps, calcium/calmodulin-regulated events, and production of active oxygen species. Indeed, some of these components involved in transducing wound signals also function in signalling other plant defence responses, suggesting that cross-talk events may regulate temporal and spatial activation of different defences.     

Roles of MAP kinase cascades in Caenorhabditis elegans

Mitogen-activated protein kinases (MAPKs) are serine/threonine protein kinases that are activated by diverse stimuli such as growth factors, cytokines, neurotransmitters and various cellular stresses. MAPK cascades are generally present as three-component modules, consisting of MAPKKK, MAPKK and MAPK. The precise molecular mechanisms by which these MAPK cascades transmit signals is an area of intense research, and our evolving understanding of these signal cascades has been facilitated in great part by genetic analyses in model organisms. One organism that has been commonly used for genetic manipulation and physiological characterization is the nematode Caenorhabditis elegans. Genes sequenced in the C. elegans genome project have furthered the identification of components involved in several MAPK pathways. Genetic and biochemical studies on these components have shed light on the physiological roles of MAPK cascades in the control of cell fate decision, neuronal function and immunity in C. elegans.