Gene regulation by MAP kinase cascades

Tomato SlMAPK3 Modulates Cold Resistance by Regulating the Synthesis of Raffinose and the Expression of SlWRKY46

Mitogen-activated protein kinase (MAPK) cascades and raffinose have been observed to increase in plants exposed to cold. However, it remains elusive whether and how MAPK regulates raffinose synthesis under cold stress. Here, overexpression of SlMAPK3 promoted the accumulation of galactinol and raffinose under cold stress, while CRISPR/Cas9-mediated mutants showed the opposite results. Moreover, SlMAPK3 promoted the expression of SlWRKY46 at low temperatures and interacted with SlWRKY46 protein. Overexpression of SlWRKY46 enhanced cold resistance. Furthermore, SlWRKY46 directly bound to the promoter of SlGols1 to enhance its expression and promoted the accumulation of raffinose. Virus-induced gene-silencing (VIGS)-mediated knockdown of SlGols1 remarkably elevated cold sensitivity and reduced raffinose content. Meanwhile, exogenous supplementation of raffinose could improve the cold tolerance of tomato plants. Thus, our data indicates that SlMAPK3 modulates cold resistance by regulating raffinose content and SlWRKY46 expression. SlWRKY46 also promotes the accumulation of raffinose by inducing the expression of SlGols1.

Genome-wide identification of the mitogen-activated kinase gene family from Limonium bicolor and functional characterization of LbMAPK2 under salt stress

BACKGROUND

Mitogen-activated protein kinases (MAPKs) are ubiquitous signal transduction components in eukaryotes. In plants, MAPKs play an essential role in growth and development, phytohormone regulation, and abiotic stress responses. The typical recretohalophyte Limonium bicolor (Bunge) Kuntze has multicellular salt glands on its stems and leaves; these glands secrete excess salt ions from its cells to mitigate salt damage. The number, type, and biological function of L. bicolor MAPK genes are unknown.

RESULTS

We identified 20 candidate L. bicolor MAPK genes, which can be divided into four groups. Of these 20 genes, 17 were anchored to 7 chromosomes, while LbMAPK18, LbMAPK19, and LbMAPK20 mapped to distinct scaffolds. Structure analysis showed that the predicted protein LbMAPK19 contains the special structural motif TNY in its activation loop, whereas the other LbMAPK members harbor the conserved TEY or TDY motif. The promoters of most LbMAPK genes carry cis-acting elements related to growth and development, phytohormones, and abiotic stress. LbMAPK1, LbMAPK2, LbMAPK16, and LbMAPK20 are highly expressed in the early stages of salt gland development, whereas LbMAPK4, LbMAPK5, LbMAPK6, LbMAPK7, LbMAPK11, LbMAPK14, and LbMAPK15 are highly expressed during the late stages. These 20 LbMAPK genes all responded to salt, drought and ABA stress. We explored the function of LbMAPK2 via virus-induced gene silencing: knocking down LbMAPK2 transcript levels in L. bicolor resulted in fewer salt glands, lower salt secretion ability from leaves, and decreased salt tolerance. The expression of several genes [LbTTG1 (TRANSPARENT TESTA OF GL1), LbCPC (CAPRICE), and LbGL2 (GLABRA2)] related to salt gland development was significantly upregulated in LbMAPK2 knockdown lines, while the expression of LbEGL3 (ENHANCER OF GL3) was significantly downregulated.

CONCLUSION

These findings increase our understanding of the LbMAPK gene family and will be useful for in-depth studies of the molecular mechanisms behind salt gland development and salt secretion in L. bicolor. In addition, our analysis lays the foundation for exploring the biological functions of MAPKs in an extreme halophyte.

Regulation of photosynthesis by mitogen-activated protein kinase in rice: antagonistic adjustment by OsMPK3 and OsMPK6

Photosynthesis is the basis of almost all life on earth and is the main component of crop yield that contributes to the carbohydrate partitioning to the grains. Maintaining the photosynthetic efficiency of plants in challenging environmental conditions by regulating the associated factors is a potential research arena which will help in the improvement of crop yield. Phosphorylation is known to play a pivotal role in the regulation of photosynthesis. Mitogen Activated Protein Kinases (MAPKs) cascade although known to regulate a diverse range of processes does not have any exact reported function in the regulation of photosynthesis. To elucidate the regulatory role of MAPKs in photosynthesis we investigated the changes in net photosynthesis rate and related parameters in DEX inducible over-expressing (OE) lines of two members of MAPK gene family namely, OsMPK3 and OsMPK6 in rice. Interestingly, significant changes were found in net photosynthesis rate and related physiological parameters in OsMPK3 and OsMPK6-OE lines compared to its wild-type relatives. OsMPK3 and OsMPK6 have regulatory effects on nuclear-encoded photosynthetic genes. Untargeted metabolite profiling reveals a higher accumulation of sugars and their derivatives in MPK6 overexpressing plants and a lower accumulation of sugars and organic acids in MPK3 overexpressing plants. The accumulation of amino acids was found in abundance in both MPK3 and MPK6 overexpressing plants. Understanding the effects of MPK3 and MPK6 on the CO2 assimilation of rice plants under normal growth conditions, will help in devising strategies that can be extended for crop improvement.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01383-9.

Comparative analysis of two kinds of garlic seedings: qualities and transcriptional landscape

BACKGROUND

Facility cultivation is widely applied to meet the increasing demand for high yield and quality, with light intensity and light quality being major limiting factors. However, how changes in the light environment affect development and quality are unclear in garlic. When garlic seedlings are grown, they can also be exposed to blanching culture conditions of darkness or low-light intensity to ameliorate their appearance and modify their bioactive compounds and flavor.

RESULTS

In this study, we determined the quality and transcriptomes of 14-day-old garlic and blanched garlic seedlings (green seedlings and blanched seedlings) to explore the mechanisms by which seedlings integrate light signals. The findings revealed that blanched garlic seedlings were taller and heavier in fresh weight compared to green garlic seedlings. In addition, the contents of allicin, cellulose, and soluble sugars were higher in the green seedlings. We also identified 3,872 differentially expressed genes between green and blanched garlic seedlings. The Kyoto Encyclopedia of Genes and Genomes analysis suggested enrichment for plant-pathogen interactions, phytohormone signaling, mitogen-activated protein kinase signaling, and other metabolic processes. In functional annotations, pathways related to the growth and formation of the main compounds included phytohormone signaling, cell wall metabolism, allicin biosynthesis, secondary metabolism and MAPK signaling. Accordingly, we identified multiple types of transcription factor genes involved in plant-pathogen interactions, plant phytohormone signaling, and biosynthesis of secondary metabolites among the differentially expressed genes between green and blanched garlic seedlings.

CONCLUSIONS

Blanching culture is one facility cultivation mode that promotes chlorophyll degradation, thus changing the outward appearance of crops, and improves their flavor. The large number of DEGs identified confirmed the difference of the regulatory machinery under two culture system. This study increases our understanding of the regulatory network integrating light and darkness signals in garlic seedlings and provides a useful resource for the genetic manipulation and cultivation of blanched garlic seedlings.

Identification and Expression Analysis of MPK and MKK Gene Families in Pecan (Carya illinoinensis)

Mitogen-activated protein kinases consist of three kinase modules composed of MPKs, MKKs, and MPKKKs. As members of the protein kinase (PK) superfamily, they are involved in various processes, such as developmental programs, cell division, hormonal progression, and signaling responses to biotic and abiotic stresses. In this study, a total of 18 MPKs and 10 MKKs were annotated on the pecan genome, all of which could be classified into four subgroups, respectively. The gene structures and conserved sequences of family members in the same branch were relatively similar. All MPK proteins had a conserved motif TxY, and D(L/I/V)K and VGTxxYMSPER existed in all MKK proteins. Duplication events contributed largely to the expansion of the pecan MPK and MKK gene families. Phylogenetic analysis of protein sequences from six plants indicated that species evolution occurred in pecan. Organ-specific expression profiles of MPK and MKK showed functional diversity. Ka/Ks values indicated that all genes with duplicated events underwent strong negative selection. Seven CiPawMPK and four CiPawMKK genes with high expression levels were screened by transcriptomic data from different organs, and these candidates were validated by qRT-PCR analysis of hormone-treated and stressed samples.

Jasmonate regulates plant resistance to Pectobacterium brasiliense by inducing indole glucosinolate biosynthesis

Pectobacterium brasiliense (P. brasiliense) is a necrotrophic bacterium that causes the soft rot disease in Brassica rapa. However, the mechanisms underlying plant immune responses against necrotrophic bacterial pathogens with a broad host range are still not well understood. Using a flg22-triggered seedling growth inhibition (SGI) assay with 455 Brassica rapa inbred lines, we selected six B. rapa flagellin-insensitive lines (Brfin2-7) and three B. rapa flagellin-sensitive lines (Brfs1-3). Brfin lines showed compromised flg22-induced immune responses (oxidative burst, mitogen-activated protein kinase (MAPK) activation, and seedling growth inhibition) compared to the control line R-o-18; nevertheless, they were resistant to P. brasiliense. To explain this, we analyzed the phytohormone content and found that most Brfin lines had higher P. brasiliense-induced jasmonic acid (JA) than Brfs lines. Moreover, MeJA pretreatment enhanced the resistance of B. rapa to P. brasiliense. To explain the correlation between the resistance of Brfin lines to P. brasiliense and activated JA signaling, we analyzed pathogen-induced glucosinolate (GS) content in B. rapa. Notably, in Brfin7, the neoglucobrassicin (NGBS) content among indole glucosinolates (IGS) was significantly higher than that in Brfs2 following P. brasiliense inoculation, and genes involved in IGSs biosynthesis were also highly expressed. Furthermore, almost all Brfin lines with high JA levels and resistance to P. brasiliense had higher P. brasiliense-induced NGBS levels than Brfs lines. Thus, our results show that activated JA-mediated signaling attenuates flg22-triggered immunity but enhances resistance to P. brasiliense by inducing indole glucosinolate biosynthesis in Brassica rapa. This study provides novel insights into the role of JA-mediated defense against necrotrophic bacterial pathogens within a broad host range.

Genome-wide identification and characterization of the MAPKKK, MKK, and MPK families in Chinese elite maize inbred line Huangzaosi

Mitogen-activated protein kinase (MAPK or MPK) cascades consist of three protein kinase components, MAPK kinase kinases (MAPKKKs), MAPK kinases (MKKs and MPKs), which are indispensable for various plant physiological processes. The functions of MAPK families have been extensively studied in maize (Zea mays L.) and other plant species, but little is known about MAPK families in the elite Chinese maize line Huangzaosi (hzs). In this study, we observed that overall performance of Huangzaosi was substantially better than that of B73 under drought conditions at the seedling and V16 stages with a favorable root/canopy ratio. In silico analyses identified 72, 10, and 24 MAPKKKs, MKKs, and MPKs, respectively, in Huangzaosi. Examinations of phylogenetic relationships among Arabidopsis thaliana (L.) Heynh., rice (Oryza sativa L.), and maize (lines B73 and hzs), gene structures, conserved protein motifs, and chromosomal locations revealed their evolutionary relationships. The basal gene expression levels and tissue specificities of all three MAPK families in hzs reflected the diversity in the MAPK functions related to growth and development. The quantitative real-time polymerase chain reaction (qPCR) assay indicated that certain MAPK genes with high basal expression levels in the primary and crown roots responded differentially to drought between B73 and hzs, suggesting that these genes may contribute to their distinct drought tolerance at different developmental stages. The important information regarding the evolution and expression of hzs MAPK family members generated in this study provides a new avenue for the better understanding on the regulatory mechanism of MAPK cascade in the core inbred line hzs, which may be useful to guide the development of new maize cultivars with desirable traits (e.g., drought resistance).

MdMKK9-Mediated the Regulation of Anthocyanin Synthesis in Red-Fleshed Apple in Response to Different Nitrogen Signals

The mitogen-activated protein kinase (MAPK) signaling cascade is a widely existing signal transduction system in eukaryotes, and plays an important role in the signal transduction processes of plant cells in response to environmental stress. In this study, we screened MdMKK9, a gene in the MAPK family. This gene is directly related to changes in anthocyanin synthesis in the ‘Daihong’ variety of red-fleshed apple (Malus sieversii f neidzwetzkyana (Dieck) Langenf). MdMKK9 expression was up-regulated in ‘Daihong’ tissue culture seedlings cultured at low levels of nitrogen. This change in gene expression up-regulated the expression of genes related to anthocyanin synthesis and nitrogen transport, thus promoting anthocyanin synthesis and causing the tissue culture seedlings to appear red in color. To elucidate the function of MdMKK9, we used the CRISPR/Cas9 system to construct a gene editing vector for MdMKK9 and successfully introduced it into the calli of the ‘Orin’ apple. The MdMKK9 deletion mutants (MUT) calli could not respond to the low level of nitrogen signal, the expression level of anthocyanin synthesis-related genes was down-regulated, and the anthocyanin content was lower than that of the wild type (WT). In contrast, the MdMKK9-overexpressed calli up-regulated the expression level of anthocyanin synthesis-related genes and increased anthocyanin content, and appeared red in conditions of low level of nitrogen or nitrogen deficiency. These results show that MdMKK9 plays a role in the adaptation of red-fleshed apple to low levels of nitrogen by regulating the nitrogen status and anthocyanin accumulation.

The Protein Phosphatase GhAP2C1 Interacts Together with GhMPK4 to Synergistically Regulate the Immune Response to Fusarium oxysporum in Cotton

The plant mitogen-activated protein kinase (MAPK) cascade plays an important role in mediating responses to biotic and abiotic stresses and is the main pathway through which extracellular stimuli are transduced intracellularly as signals. Our previous research showed that the GhMKK6-GhMPK4 cascade signaling pathway plays an important role in cotton immunity. To further analyze the role and regulatory mechanism of the GhMKK6-GhMPK4 cascade signaling pathway in cotton resistance to Fusarium wilt, we functionally analyzed GhMPK4. Our results show that silencing GhMPK4 reduces cotton tolerance to Fusarium wilt and reduces the expression of several resistance genes. Further experiments revealed that GhMPK4 is similar to GhMKK6, both of whose overexpression cause unfavorable cotton immune response characteristics. By using a yeast two-hybrid screening library and performing a bioinformatics analysis, we screened and identified a negative regulator of the MAPK kinase-protein phosphatase AP2C1. Through the functional analysis of AP2C1, it was found that, after being silenced, GhAP2C1 increased resistance to Fusarium wilt, but GhAP2C1 overexpression caused sensitivity to Fusarium wilt. These findings show that GhAP2C1 interacts together with GhMPK4 to regulate the immune response of cotton to Fusarium oxysporum, which provides important data for functionally analyzing and studying the feedback regulatory mechanism of the MAPK cascade and helps to clarify the regulatory mechanism through which the MAPK cascade acts in response to pathogens.

Genomic and Transcriptomic Analysis Provide Insights Into Root Rot Resistance in Panax notoginseng

Panax notoginseng (Panax notoginseng (Burk.) F.H. Chen), a plant of high medicinal value, is severely affected by root rot during cultivation. Here, we generated a reference genome of P. notoginseng, with a contig N50 size of 241.268 kb, and identified 66 disease-resistance genes (R-genes) as candidate genes for breeding disease-resistant varieties. We then investigated the molecular mechanism underlying the responses of resistant and susceptible P. notoginseng genotypes to Fusarium oxysporum infection at six time points by RNA-seq. Functional analysis of the genes differentially expressed between the two genotypes indicated that genes involved in the defense response biological process like hormone transduction and plant-pathogen interaction are continuously and highly expressed in resistant genotype during infection. Moreover, salicylic acid and jasmonic acid levels gradually increased during infection in the resistant genotype. Coexpression analysis showed that PnWRKY22 acts as a hub gene in the defense response of the resistant genotype. Finally, transiently overexpressing PnWRKY22 increased salicylic acid levels in P. notoginseng leaves. Our findings provide a theoretical basis for studying root rot resistance in P. notoginseng.

Effects of MPK3 and MPK6 kinases on the chloroplast architecture and function induced by cold acclimation in Arabidopsis

Exposure to low, non-freezing temperatures develops freezing tolerance in many plant species. Such process is called cold acclimation. Molecular changes undergone during cold acclimation are orchestrated by signalling networks including MAP kinases. Structure and function of chloroplasts are affected by low temperatures. The aim of this work was to study how the MAP kinases MPK3 and MPK6 are involved in the chloroplast performance upon a long period of cold acclimation. We used Arabidopsis thaliana wild type and mpk3 and mpk6 mutants. Adult plants were acclimated during 7 days at 4 °C and then measurements of PSII performance and chloroplast ultrastructure were carried out. Only the mpk6 acclimated plants showed a high freezing sensitivity. No differences in the PSII function were observed in the plants from the three genotypes exposed to non-acclimated or acclimated conditions. The acclimation of wild-type plants produced severe alterations in the ultrastructure of chloroplast and thylakoids, which was more accentuated in the mpk plants. However, only the mpk6 mutant was unable to internalize the damaged chloroplasts into the vacuole. These results indicate that cold acclimation induces alterations in the chloroplast architecture leading to preserve an optimal performance of PSII. MPK3 and MPK6 are necessary to regulate these morphological changes, but besides, MPK6 is needed to the vacuolization of the damaged chloroplasts, suggesting a role in the chloroplast recycling during cold acclimation. The latter could be quite relevant, since it could explain why this mutant is the only one showing an extremely low freezing tolerance.

Mitogen-Activated Protein Kinase Expression Profiling Revealed Its Role in Regulating Stress Responses in Potato (Solanum tuberosum)

Mitogen-activated protein kinase (MAPK) cascades are the universal signal transduction networks that regulate cell growth and development, hormone signaling, and other environmental stresses. However, their essential contribution to plant tolerance is very little known in the potato (Solanum tuberosum) plant. The current study carried out a genome-wide study of StMAPK and provided a deep insight using bioinformatics tools. In addition, the relative expression of StMAPKs was also assessed in different plant tissues. The similarity search results identified a total of 22 StMAPK genes in the potato genome. The sequence alignment also showed conserved motif TEY/TDY in most StMAPKs with conserved docking LHDXXEP sites. The phylogenetic analysis divided all 22 StMAPK genes into five groups, i.e., A, B, C, D, and E, showing some common structural motifs. In addition, most of the StMAPKs were found in a cluster form at the terminal of chromosomes. The promoter analysis predicted several stress-responsive Cis-acting regulatory elements in StMAPK genes. Gene duplication under selection pressure also indicated several purifying and positive selections in StMAPK genes. In potato, StMAPK2, StMAPK6, and StMAPK19 showed a high expression in response to heat stress. Under ABA and IAA treatment, the expression of the total 20 StMAPK genes revealed that ABA and IAA played an essential role in this defense process. The expression profiling and real-time qPCR (RT-qPCR) exhibited their high expression in roots and stems compared to leaves. These results deliver primary data for functional analysis and provide reference data for other important crops.

Molecular characterization, expression and interaction of MAPK, MAPKK and MAPKKK genes in upland cotton

Mitogen-activated protein kinase (MAPK) signaling cascades, consisting of three types of sequentially phosphorylated kinases (MAPKKK, MAPKK, and MAPK), play vital roles in various processes including plant development and stress response. In this study, 52 GhMAPKs, 23 GhMAPKKs, and 166 GhMAPKKKs were identified in upland cotton. Chromosomal locations, gene duplication and structure, motifs, cis-regulatory elements, and protein subcellular localization were further analyzed. With the identified MAPK cascade genes in G. arboretum and G. raimondii, a syntenic diagram of three cotton species was constructed. The interactions of seven GhMAPK cascade genes were investigated. Two complete signaling modules were defined: The GhMEKK24/GhMEKK31-GhMAPKK9-GhMAPK10 and GhMEKK3/GhMEKK24/GhMEKK31-GhMAPKK16-GhMAPK10/GhMAPK11 cascades. Moreover, interaction networks and the interaction pairs were combined with their expression patterns and demonstrated that the network mediated by the MAPK signaling cascade participates in abiotic stress signaling. Our research provides a foundation for studying the molecular mechanism of the MAPK signaling pathway under abiotic stress.

Transcriptome-IPMS analysis reveals a tissue-dependent miR156/SPL13 regulatory mechanism in alfalfa drought tolerance

Background

We previously reported on the interplay between miR156/SPL13 and WD40–1/DFR to improve response to drought stress in alfalfa (Medicago sativa L.). Here we aimed to investigate whether the role of miR156/SPL13 module in drought response is tissue-specific, and to identify SPL13-interacting proteins. We analyzed the global transcript profiles of leaf, stem, and root tissues of one-month old RNAi-silenced SPL13 (SPL13RNAi) alfalfa plants exposed to drought stress and conducted protein-protein interaction analysis to identify SPL13 interacting partners.

Result

Transcript analysis combined with weighted gene co-expression network analysis showed tissue and genotype-specific gene expression patterns. Moreover, pathway analysis of stem-derived differentially expressed genes (DEG) revealed upregulation of genes associated with stress mitigating primary and specialized metabolites, whereas genes associated with photosynthesis light reactions were silenced in SPL13RNAi plants. Leaf-derived DEG were attributed to enhanced light reactions, largely photosystem I, II, and electron transport chains, while roots of SPL13RNAi plants upregulated transcripts associated with metal ion transport, carbohydrate, and primary metabolism. Using immunoprecipitation combined with mass spectrometry (IPMS) we showed that SPL13 interacts with proteins involved in photosynthesis, specialized metabolite biosynthesis, and stress tolerance.

Conclusions

We conclude that the miR156/SPL13 module mitigates drought stress in alfalfa by regulating molecular and physiological processes in a tissue-dependent manner.

Scaffold protein GhMORG1 enhances the resistance of cotton to Fusarium oxysporum by facilitating the MKK6-MPK4 cascade

In eukaryotes, MAPK scaffold proteins are crucial for regulating the function of MAPK cascades. However, only a few MAPK scaffold proteins have been reported in plants, and the molecular mechanism through which scaffold proteins regulate the function of the MAPK cascade remains poorly understood. Here, we identified GhMORG1, a GhMKK6-GhMPK4 cascade scaffold protein that positively regulates the resistance of cotton to Fusarium oxysporum. GhMORG1 interacted with GhMKK6 and GhMPK4, and the overexpression of GhMORG1 in cotton protoplasts dramatically increased the activity of the GhMKK6-GhMPK4 cascade. Quantitative phosphoproteomics was used to clarify the mechanism of GhMORG1 in regulating disease resistance, and thirty-two proteins were considered as the putative substrates of the GhMORG1-dependent GhMKK6-GhMPK4 cascade. These putative substrates were involved in multiple disease resistance processes, such as cellular amino acid metabolic processes, calcium ion binding and RNA binding. The kinase assays verified that most of the putative substrates were phosphorylated by the GhMKK6-GhMPK4 cascade. For functional analysis, nine putative substrates were silenced in cotton, respectively. The resistance of cotton to F. oxysporum was decreased in the substrate-silenced cottons. These results suggest that GhMORG1 regulates several different disease resistance processes by facilitating the phosphorylation of GhMKK6-GhMPK4 cascade substrates. Taken together, these findings reveal a new plant MAPK scaffold protein and provide insights into the mechanism of plant resistance to pathogens.

The MAP3K-Coding QUI-GON JINN (QGJ) Gene Is Essential to the Formation of Unreduced Embryo Sacs in Paspalum

Apomixis is a clonal mode of reproduction via seeds, which results from the failure of meiosis and fertilization in the sexual female reproductive pathway. In previous transcriptomic surveys, we identified a mitogen-activated protein kinase kinase kinase (N46) displaying differential representation in florets of sexual and apomictic Paspalum notatum genotypes. Here, we retrieved and characterized the N46 full cDNA sequence from sexual and apomictic floral transcriptomes. Phylogenetic analyses showed that N46 was a member of the YODA family, which was re-named QUI-GON JINN (QGJ). Differential expression in florets of sexual and apomictic plants was confirmed by qPCR. In situ hybridization experiments revealed expression in the nucellus of aposporous plants' ovules, which was absent in sexual plants. RNAi inhibition of QGJ expression in two apomictic genotypes resulted in significantly reduced rates of aposporous embryo sac formation, with respect to the level detected in wild type aposporous plants and transformation controls. The QGJ locus segregated independently of apospory. However, a probe derived from a related long non-coding RNA sequence (PN_LNC_QGJ) revealed RFLP bands cosegregating with the Paspalum apospory-controlling region (ACR). PN_LNC_QGJ is expressed in florets of apomictic plants only. Our results indicate that the activity of QGJ in the nucellus of apomictic plants is necessary to form non-reduced embryo sacs and that a long non-coding sequence with regulatory potential is similar to sequences located within the ACR.

CaSK23, a Putative GSK3/SHAGGY-Like Kinase of Capsicum annuum, Acts as a Negative Regulator of Pepper's Response to Ralstonia solanacearum Attack

GSK3-like kinases have been mainly implicated in the brassinosteroids (BR) pathway and, therefore, in plant growth, development, and responses to abiotic stresses; however, their roles in plant immunity remain poorly understood. Herein, we present evidence that CaSK23, a putative GSK3/SHAGGY-like kinase in pepper, acts as a negative regulator in pepper’s response to Ralstonia solanacearum (R. solanacearum) inoculation (RSI). Data from quantitative RT-PCR (qRT-PCR) showed that the constitutively-expressed CaSK23 in pepper leaves was down-regulated by RSI, as well as by exogenously-applied salicylic acid (SA) or methyl jasomonate (MeJA). Silencing of CaSK23 by virus-induced gene silencing (VIGS) decreased the susceptibility of pepper plants to RSI, coupled with up-regulation of the tested genes encoding SA-, JA-, and ethylene (ET)-dependent pathogenesis-related (PR) proteins. In contrast, ectopic overexpression (OE) of CaSK23 conferred a compromised resistance of tobacco plants to RSI, accompanied by down-regulation of the tested immunity-associated SA-, JA-, and ET-dependent PR genes. In addition, transient overexpression of CaSK23 in pepper plants consistently led to down-regulation of the tested SA-, JA-, and ET-dependent PR genes. We speculate that CaSK23 acts as a negative regulator in pepper immunity and its constitutive expression represses pepper immunity in the absence of pathogens. On the other hand, its decreased expression derepresses immunity when pepper plants are attacked by pathogens.

Transcriptomics comparison reveals the diversity of ethylene and methyl-jasmonate in roles of TIA metabolism in Catharanthus roseus

Background

The medicinal plant, Catharanthus roseus (C. roseus), accumulates a wide range of terpenoid indole alkaloids (TIAs). Ethylene (ET) and methyl-jasmonate (MeJA) were previously reported as effective elicitors for the production of various valuable secondary metabolites of C. roseus, while a few ET or MeJA induced transcriptomic research is yet reported on this species. In this study, the de-novo transcriptome assembly of C. roseus is performed by using the next-generation sequencing technology.

Results

The result shows that phenolic biosynthesis genes respond specifically to ET in leaves, monoterpenoid biosynthesis genes respond specifically to MeJA in roots. By screening the database, 23 ATP-binding cassette (ABC) transporter partial sequences are identified in C. roseus. On this basis, more than 80 key genes that encode key enzymes (namely TIA pathway, transcriptional factor (TF) and candidate ABC transporter) of alkaloid synthesis in TIA biosynthetic pathways are chosen to explore the integrative responses to ET and MeJA at the transcriptional level. Our data indicated that TIA accumulation is strictly regulated by the TF ethylene responsive factor (ERF) and bHLH iridoid synthesis 1 (BIS1). The heatmap, combined with principal component analysis (PCA) of C. roseus, shows that ERF co-expression with ABC2 and ABC8 specific expression in roots affect the root-specific accumulation of vinblastine in C. roseus. On the contrast, BIS1 activities follow a similar pattern of ABC3 and CrTPT2 specific expression in leaves, which affects the leaf-specific accumulation of vindoline in C. roseus.

Conclusions

Results presented above illustrate that ethylene has a stronger effect than MeJA on TIA induction at both transcriptional and metabolite level. Furthermore, meta-analysis reveals that ERF and BIS1 form a positive feedback loop connecting two ABC transporters respectively and are actively involved in TIAs responding to ET and MeJA in C. roseus.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4879-3) contains supplementary material, which is available to authorized users.

Mitogen activated protein kinase 6 and MAP kinase phosphatase 1 are involved in the response of Arabidopsis roots to L-glutamate

The function and components of L-glutamate signaling pathways in plants have just begun to be elucidated. Here, using a combination of genetic and biochemical strategies, we demonstrated that a MAPK module is involved in the control of root developmental responses to this amino acid. Root system architecture plays an essential role in plant adaptation to biotic and abiotic factors via adjusting signal transduction and gene expression. L-Glutamate (L-Glu), an amino acid with neurotransmitter functions in animals, inhibits root growth, but the underlying genetic mechanisms are poorly understood. Through a combination of genetic analysis, in-gel kinase assays, detailed cell elongation and division measurements and confocal analysis of expression of auxin, quiescent center and stem cell niche related genes, the critical roles of L-Glu in primary root growth acting through the mitogen-activated protein kinase 6 (MPK6) and the dual specificity serine-threonine-tyrosine phosphatase MKP1 could be revealed. In-gel phosphorylation assays revealed a rapid and dose-dependent induction of MPK6 and MPK3 activities in wild-type Arabidopsis seedlings in response to L-Glu. Mutations in MPK6 or MKP1 reduced or increased root cell division and elongation in response to L-Glu, possibly modulating auxin transport and/or response, but in a PLETHORA1 and 2 independent manner. Our data highlight MPK6 and MKP1 as components of an L-Glu pathway linking the auxin response, and cell division for primary root growth.

Activation of MAP kinases by green leaf volatiles in grasses

Objective

Previously we have shown that mechanical wounding and volatiles released from cut grass, activated a 46 and 44 kDa mitogen-activated protein kinase (MAPK) in the model grass species Lolium temulentum (Lt). MAPKs play an important role as signal relays that connect incoming stress signals and stress responses. Since green leaf volatiles (GLV) are released during wounding, we wanted determine if specific compounds contained in the GLV mixture or if GLV generated from other plant species could activate these Lt MAPKs.

Results

Our analysis found that just a 1-min exposure to GLV was enough to activate the Lt 46 kDa MAPK within 3 min and the 44 kDa MAPK within 15 min. This activation pattern showed similar kinetics to those observed after wounding, and the GLV and wound activated bands associated with these MAPKs displayed identical migration on sodium dodecyl sulfate polyacrylamide gels. Thirteen different commercially available plant volatiles (alcohols, aldehydes and ketones) were tested and all thirteen volatile compounds were able to activate these same Lt MAPKs. Furthermore, GLV derived from three other grass species as well as tomato, a dicot, were also shown to activate these MAPKs in Lt.

Electronic supplementary material

The online version of this article (10.1186/s13104-017-3076-9) contains supplementary material, which is available to authorized users.

Genome-Wide Identification of Mitogen-activated Protein Kinase Cascade Genes and Transcriptional Profiling Analysis during Organ Development in Eucommia ulmoides

The mitogen-activated protein kinase (MAPK) cascades, which play crucial roles in plant development processes, are universal modules of signal transduction in eukaryotes and consist of a core module of three sequentially phosphorylated kinases: MAPK, MAPK kinase (MAPKK), and MAPKK kinase (MAPKKK). This is the first report on the identification and analysis of MAPK cascades in Eucommia ulmoides. We conducted a genome-wide screening and identified 13 EuMAPKs, five EuMAPKKs, and 57 EuMAPKKKs. The construction of phylogenetic trees revealed that EuMAPKs and EuMAPKKs were divided into four groups (A, B, C, and D), and EuMAPKKKs were divided into three subfamilies (MEKK, RAF, and ZIK). These subfamilies were further confirmed by conserved domain/motif analysis and gene structure analysis. Based on the expression profiles of all identified EuMAPK cascades in various organs at different developmental stages, three genes (EuRAF22-2, EuRAF34-1, and EuRAF33-2) with stable expression patterns at all stages of fruit or leaf development, three genes (EuRAF2-3, EuMPK11, and EuMEKK21) with differential expression patterns, and two highly expressed genes (EuZIK1 and EuMKK2) were screened and validated by qRT-PCR. Overall, our results could be used for further research on the precise role of MAPK cascades during organ development in E. ulmoides.

Transcriptome analysis of Crossostephium chinensis provides insight into the molecular basis of salinity stress responses

Soil salinization is becoming a limitation to the utilization of ornamental plants worldwide. Crossostephium chinensis (Linnaeus) Makino is often cultivated along the southeast coast of China for its desirable ornamental qualities and high salt tolerance. However, little is known about the genomic background of the salt tolerance mechanism in C. chinensis. In the present study, we used Illumina paired-end sequencing to systematically investigate leaf transcriptomes derived from C. chinensis seedlings grown under normal conditions and under salt stress. A total of 105,473,004 bp of reads were assembled into 163,046 unigenes, of which 65,839 (40.38% of the total) and 54,342 (33.32% of the total) were aligned in Swiss-Prot and Nr protein, respectively. A total of 11,331 (6.95%) differentially expressed genes (DEGs) were identified among three comparisons, including 2,239 in ‘ST3 vs ST0’, 5,880 in ‘ST9 vs ST3’ and 9,718 in ‘ST9 vs ST0’, and they were generally classified into 26 Gene Ontology terms and 58 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway terms. Many genes encoding important transcription factors (e.g., WRKY, MYB, and AP2/EREBP) and proteins involved in starch and sucrose metabolism, arginine and proline metabolism, plant hormone signal transduction, amino acid biosynthesis, plant-pathogen interactions and carbohydrate metabolism, among others, were substantially up-regulated under salt stress. These genes represent important candidates for studying the salt-response mechanism and molecular biology of C. chinensis and its relatives. Our findings provide a genomic sequence resource for functional genetic assignments in C. chinensis. These transcriptome datasets will help elucidate the molecular mechanisms responsible for salt-stress tolerance in C. chinensis and facilitate the breeding of new stress-tolerant cultivars for high-saline areas using this valuable genetic resource.

Activation of ZmMKK10, a maize mitogen-activated protein kinase kinase, induces ethylene-dependent cell death

Mitogen-activated protein kinase (MAPK) cascades play important roles in regulating plant growth, development and stress responses. Here, we report that ZmMKK10, a maize MAP kinase kinase, positively regulates cell death. Sequence comparison to Arabidopsis MKKs has led to ZmMKK10 being classified as a group D MKK. Kinase activity analysis of recombinant ZmMKK10 showed that the Mg²⁺ ion was required for its kinase activity. Transient expression of ZmMKK10^WT or ZmMKK10^DD (the active form of ZmMKK10) in maize mesophyll protoplast significantly increased the cell death rate. Inducible expression of ZmMKK10^WT or ZmMKK10^DD in Arabidopsis transgenic plants caused rapid HR-like cell death, whereas induction of ZmMKK10^KR (the inactive form of ZmMKK10) expression in transgenic plants did not yield the same phenotype. Genetic and pharmacological analysis revealed that ZmMKK10-induced cell death in transgenic plants requires the activation of Arabidopsis MPK3 and MPK6 and that it partially depended on ethylene biosynthesis. ZmMPK3 and ZmMPK7, the orthologues of Arabidopsis MPK3 and MPK6, interacted with ZmMKK10 in yeast and ZmMKK10 phosphorylated them both in vitro. Our results demonstrate that ZmMKK10 induces cell death in an ethylene-dependent manner. Furthermore, ZmMPK3 and ZmMPK7 may be the downstream MAPKs in this process.

Global Identification, Classification, and Expression Analysis of MAPKKK genes: Functional Characterization of MdRaf5 Reveals Evolution and Drought-Responsive Profile in Apple

Mitogen-activated protein kinase kinase kinases (MAPKKKs) are pivotal components of Mitogen-activated protein kinase (MAPK) cascades, which play a significant role in many biological processes. Although genome-wide analysis of MAPKKKs has been conducted in many species, extant results in apple are scarce. In this study, a total of 72 putative MdMAPKKKs in Raf-like group, 11 in ZIK-like group and 37 in MEEK were identified in apple firstly. Predicted MdMAPKKKs were located in 17 chromosomes with diverse densities, and there was a high-level of conservation in and among the evolutionary groups. Encouragingly, transcripts of 12 selected MdMAPKKKs were expressed in at least one of the tested tissues, indicating that MdMAPKKKs might participate in various physiological and developmental processes in apple. Moreover, they were found to respond to drought stress in roots and leaves, which suggested a possible conserved response to drought stress in different species. Overexpression of MdRaf5 resulted in a hyposensitivity to drought stress, which was at least partially due to the regulation of stomatal closure and transpiration rates. To the best of our knowledge, this is the first genome-wide functional analysis of the MdMAPKKK genes in apple, and it provides valuable information for understanding MdMAPKKKs signals and their putative functions.

Expression Profiling of Mitogen-Activated Protein Kinase Genes Reveals Their Evolutionary and Functional Diversity in Different Rubber Tree (Hevea brasiliensis) Cultivars

Rubber tree (Heveabrasiliensis) is the only commercially cultivated plant for producing natural rubber, one of the most essential industrial raw materials. Knowledge of the evolutionary and functional characteristics of kinases in H. brasiliensis is limited because of the long growth period and lack of well annotated genome information. Here, we reported mitogen-activated protein kinases in H. brasiliensis (HbMPKs) by manually checking and correcting the rubber tree genome. Of the 20 identified HbMPKs, four members were validated by proteomic data. Protein motif and phylogenetic analyses classified these members into four known groups comprising Thr-Glu-Tyr (TEY) and Thr-Asp-Tyr (TDY) domains, respectively. Evolutionary and syntenic analyses suggested four duplication events: HbMPK3/HbMPK6, HbMPK8/HbMPK9/HbMPK15, HbMPK10/HbMPK12 and HbMPK11/HbMPK16/HbMPK19. Expression profiling of the identified HbMPKs in roots, stems, leaves and latex obtained from three cultivars with different latex yield ability revealed tissue- and variety-expression specificity of HbMPK paralogues. Gene expression patterns under osmotic, oxidative, salt and cold stresses, combined with cis-element distribution analyses, indicated different regulation patterns of HbMPK paralogues. Further, Ka/Ks and Tajima analyses suggested an accelerated evolutionary rate in paralogues HbMPK10/12. These results revealed HbMPKs have diverse functions in natural rubber biosynthesis, and highlighted the potential possibility of using MPKs to improve stress tolerance in future rubber tree breeding.

Molecular and biochemical characterization of a Vigna mungo MAP kinase associated with Mungbean Yellow Mosaic India Virus infection and deciphering its role in restricting the virus multiplication

Yellow Mosaic Disease caused by the begomovirus Mungbean Yellow Mosaic India Virus (MYMIV) severely affects many economically important legumes. Recent investigations in Vigna mungo - MYMIV incompatible interaction identified a MAPK homolog in the defense signaling pathway. An important branch of immunity involves phosphorylation by evolutionary conserved Mitogen-activated protein kinases (MAPK) that transduce signals of pathogen invasion to downstream molecules leading to diverse immune responses. However, most of the knowledge of MAPKs is derived from model crops, and functions of these versatile kinases are little explored in legumes. Here we report characterization of a MAP kinase (VmMAPK1), which was induced upon MYMIV-inoculation in resistant V. mungo. Phylogenetic analysis revealed that VmMAPK1 is closely related to other plant-stress-responsive MAPKs. Both mRNA and protein of VmMAPK1 were accumulated upon MYMIV infection. The VmMAPK1 protein localized in the nucleus as well as cytoplasm and possessed phosphorylation activity in vitro. A detailed biochemical characterization of purified recombinant VmMAPK1 demonstrated an intramolecular mechanism of autophosphorylation and self-catalyzed phosphate incorporation on both threonine and tyrosine residues. The V_max and K_m values of recombinant VmMAPK1 for ATP were 6.292nmol/mg/min and 0.7978μM, respectively. Furthermore, the ability of VmMAPK1 to restrict MYMIV multiplication was validated by its ectopic expression in transgenic tobacco. Importantly, overexpression of VmMAPK1 resulted in the considerable upregulation of defense-responsive marker PR genes. Thus, the present data suggests the critical role of VmMAPK1 in suppressing MYMIV multiplication presumably through SA-mediated signaling pathway and inducing PR genes establishing the significant implications in understanding MAP kinase gene function during Vigna-MYMIV interaction; and hence paves the way for introgression of resistance in leguminous crops susceptible to MYMIV.

Chitin and Stress Induced Protein Kinase Activation

The assays described here are pertinent to protein kinase studies in any plant. They include an immunoblot phosphorylation/activation assay and an in-gel activity assay for MAP kinases (MPKs) using the general protein kinase substrate myelin basic protein. They also include a novel in-gel peptide substrate assay for Snf1-related kinase family 2 members (SnRK2s). This kinase family-specific assay overcomes some limitations of in-gel assays and permits the identification of different types of kinase activities in total protein extracts.

WRKY transcription factors in plant responses to stresses

The WRKY gene family is among the largest families of transcription factors (TFs) in higher plants. By regulating the plant hormone signal transduction pathway, these TFs play critical roles in some plant processes in response to biotic and abiotic stress. Various bodies of research have demonstrated the important biological functions of WRKY TFs in plant response to different kinds of biotic and abiotic stresses and working mechanisms. However, very little summarization has been done to review their research progress. Not just important TFs function in plant response to biotic and abiotic stresses, WRKY also participates in carbohydrate synthesis, senescence, development, and secondary metabolites synthesis. WRKY proteins can bind to W-box (TGACC (A/T)) in the promoter of its target genes and activate or repress the expression of downstream genes to regulate their stress response. Moreover, WRKY proteins can interact with other TFs to regulate plant defensive responses. In the present review, we focus on the structural characteristics of WRKY TFs and the research progress on their functions in plant responses to a variety of stresses.

Adaptation Mechanisms in the Evolution of Moss Defenses to Microbes

Bryophytes, including mosses, liverworts and hornworts are early land plants that have evolved key adaptation mechanisms to cope with abiotic stresses and microorganisms. Microbial symbioses facilitated plant colonization of land by enhancing nutrient uptake leading to improved plant growth and fitness. In addition, early land plants acquired novel defense mechanisms to protect plant tissues from pre-existing microbial pathogens. Due to its evolutionary stage linking unicellular green algae to vascular plants, the non-vascular moss Physcomitrella patens is an interesting organism to explore the adaptation mechanisms developed in the evolution of plant defenses to microbes. Cellular and biochemical approaches, gene expression profiles, and functional analysis of genes by targeted gene disruption have revealed that several defense mechanisms against microbial pathogens are conserved between mosses and flowering plants. P. patens perceives pathogen associated molecular patterns by plasma membrane receptor(s) and transduces the signal through a MAP kinase (MAPK) cascade leading to the activation of cell wall associated defenses and expression of genes that encode proteins with different roles in plant resistance. After pathogen assault, P. patens also activates the production of ROS, induces a HR-like reaction and increases levels of some hormones. Furthermore, alternative metabolic pathways are present in P. patens leading to the production of a distinct metabolic scenario than flowering plants that could contribute to defense. P. patens has acquired genes by horizontal transfer from prokaryotes and fungi, and some of them could represent adaptive benefits for resistance to biotic stress. In this review, the current knowledge related to the evolution of plant defense responses against pathogens will be discussed, focusing on the latest advances made in the model plant P. patens.

Divergent evolutionary patterns of the MAPK cascade genes in Brassica rapa and plant phylogenetics

Mitogen-activated protein kinase (MAPK) cascade signal transduction modules play crucial roles in regulating many biological processes in plants. These cascades are composed of three classes of hierarchically organized protein kinases, MAPKKKs, MAPKKs and MAPKs. Here, we analyzed gene retention, phylogenetic, evolution and expression patterns of MAPK cascade genes in Brassica rapa. We further found that the MAPK branches, classes III and IV, appeared after the split of bryophytes and green algae after analyzing the MAPK cascade genes in 8 species, and their rapid expansion led to the great size of the families of MAPKs. In contrast, the ancestral class I subfamily of MAPKK gene families have been highly conserved from algae to angiosperms. For the MAPKKK family, the MEKK and Raf subfamily share a common evolutionary origin, and Raf plays a major role in the expansion of the MAPKKK gene family. The cis-elements and interaction network analyses showed the important function of MAPK cascade genes in development and stress responses in B. rapa. This study provides a solid foundation for molecular evolution analyses of MAPK cascade genes.

Molecular characterization of biotic and abiotic stress-responsive MAP kinase genes, IbMPK3 and IbMPK6, in sweetpotato

Plants are continually exposed to numerous environmental stresses. To decrease damage caused by these potentially detrimental factors, various stress-related signaling cascades are activated in plants. One such stress-responsive signaling pathway, the mitogen-activated protein kinase (MAPK) module, plays a critical role in diverse plant stress responses. Here, we functionally characterized biotic and abiotic stress-responsive MAPK genes, IbMPK3 and IbMPK6, from sweetpotato. IbMPK3/6 contain totally 11 MAPK conserved subdomains and the phosphorylating motif TEY. Bacterially expressed IbMPK3/6 could be autophosphorylated in vitro, and these proteins phosphorylated universal kinase substrate, such as myelin basic protein. IbMPK3/6 transcripts were expressed in leaf, stem, and root of sweetpotato cultivars with storage roots of various colors. IbMPK3 and IbMPK6 were induced by various biotic/abiotic stress treatments. Furthermore, the kinase activity of IbMPK3/6 was induced during early NaCl, SA, H2O2, and ABA treatment. IbMPK3/6 were predominantly localized to the nucleus. To determine the biological functions of IbMPK3/6, we transiently expressed the IbMPK genes in tobacco (Nicotiana benthamiana) leaves, which resulted in enhanced tolerance to bacterial pathogen and increased expression of pathogenesis-related (PR) genes. These data demonstrate that IbMPK3 and IbMPK6 play significant roles in plant responses to environmental stress.

Genome-wide identification, phylogeny and expressional profiles of mitogen activated protein kinase kinase kinase (MAPKKK) gene family in bread wheat (Triticum aestivum L.)

BACKGROUND

Mitogen-activated protein kinase kinase kinases (MAPKKKs) are the important components of MAPK cascades, which play the crucial role in plant growth and development as well as in response to diverse stresses. Although this family has been systematically studied in many plant species, little is known about MAPKKK genes in wheat (Triticum aestivum L.), especially those involved in the regulatory network of stress processes.

RESULTS

In this study, we identified 155 wheat MAPKKK genes through a genome-wide search method based on the latest available wheat genome information, of which 29 belonged to MEKK, 11 to ZIK and 115 to Raf subfamily, respectively. Then, chromosome localization, gene structure and conserved protein motifs and phylogenetic relationship as well as regulatory network of these TaMAPKKKs were systematically investigated and results supported the prediction. Furthermore, a total of 11 homologous groups between A, B and D sub-genome and 24 duplication pairs among them were detected, which contributed to the expansion of wheat MAPKKK gene family. Finally, the expression profiles of these MAPKKKs during development and under different abiotic stresses were investigated using the RNA-seq data. Additionally, 10 tissue-specific and 4 salt-responsive TaMAPKKK genes were selected to validate their expression level through qRT-PCR analysis.

CONCLUSIONS

This study for the first time reported the genome organization, evolutionary features and expression profiles of the wheat MAPKKK gene family, which laid the foundation for further functional analysis of wheat MAPKKK genes, and contributed to better understanding the roles and regulatory mechanism of MAPKKKs in wheat.

Plastid-nucleus communication involves calcium-modulated MAPK signalling

Chloroplast retrograde signals play important roles in coordinating the plastid and nuclear gene expression and are critical for proper chloroplast biogenesis and for maintaining optimal chloroplast functions in response to environmental changes in plants. Until now, the signals and the mechanisms for retrograde signalling remain poorly understood. Here we identify factors that allow the nucleus to perceive stress conditions in the chloroplast and to respond accordingly by inducing or repressing specific nuclear genes encoding plastid proteins. We show that ABI4, which is known to repress the LHCB genes during retrograde signalling, is activated through phosphorylation by the MAP kinases MPK3/MPK6 and the activity of these kinases is regulated through 14-3-3ω-mediated Ca(2+)-dependent scaffolding depending on the chloroplast calcium sensor protein CAS. These findings uncover an additional mechanism in which chloroplast-modulated Ca(2+) signalling controls the MAPK pathway for the activation of critical components of the retrograde signalling chain.

Benzoylsalicylic acid isolated from seed coats of Givotia rottleriformis induces systemic acquired resistance in tobacco and Arabidopsis

Systemic acquired resistance (SAR), a whole plant defense response to a broad spectrum of pathogens, is characterized by a coordinated expression of a large number of defense genes. Plants synthesize a variety of secondary metabolites to protect themselves from the invading microbial pathogens. Several studies have shown that salicylic acid (SA) is a key endogenous component of local and systemic disease resistance in plants. Although SA is a critical signal for SAR, accumulation of endogenous SA levels alone is insufficient to establish SAR. Here, we have identified a new acyl derivative of SA, the benzoylsalicylic acid (BzSA) also known as 2-(benzoyloxy) benzoic acid from the seed coats of Givotia rottleriformis and investigated its role in inducing SAR in tobacco and Arabidopsis. Interestingly, exogenous BzSA treatment induced the expression of NPR1 (Non-expressor of pathogenesis-related gene-1) and pathogenesis related (PR) genes. BzSA enhanced the expression of hypersensitivity related (HSR), mitogen activated protein kinase (MAPK) and WRKY genes in tobacco. Moreover, Arabidopsis NahG plants that were treated with BzSA showed enhanced resistance to tobacco mosaic virus (TMV) as evidenced by reduced leaf necrosis and TMV-coat protein levels in systemic leaves. We, therefore, conclude that BzSA, hitherto unknown natural plant product, is a new SAR inducer in plants.

An Innate Immunity Pathway in the Moss Physcomitrella patens

MAP kinase (MPK) cascades in Arabidopsis thaliana and other vascular plants are activated by developmental cues, abiotic stress, and pathogen infection. Much less is known of MPK functions in nonvascular land plants such as the moss Physcomitrella patens Here, we provide evidence for a signaling pathway in P. patens required for immunity triggered by pathogen associated molecular patterns (PAMPs). This pathway induces rapid growth inhibition, a novel fluorescence burst, cell wall depositions, and accumulation of defense-related transcripts. Two P. patens MPKs (MPK4a and MPK4b) are phosphorylated and activated in response to PAMPs. This activation in response to the fungal PAMP chitin requires a chitin receptor and one or more MAP kinase kinase kinases and MAP kinase kinases. Knockout lines of MPK4a appear wild type but have increased susceptibility to the pathogenic fungi Botrytis cinerea and Alternaria brassisicola Both PAMPs and osmotic stress activate some of the same MPKs in Arabidopsis. In contrast, abscisic acid treatment or osmotic stress of P. patens does not activate MPK4a or any other MPK, but activates at least one SnRK2 kinase. Signaling via MPK4a may therefore be specific to immunity, and the moss relies on other pathways to respond to osmotic stress.

Genome-Wide Identification, Evolution, and Co-expression Network Analysis of Mitogen-Activated Protein Kinase Kinase Kinases in Brachypodium distachyon

Mitogen-activated protein kinase (MAPK) cascades are the conserved and universal signal transduction modules in all eukaryotes, which play the vital roles in plant growth, development, and in response to multiple stresses. In this study, we used bioinformatics methods to identify 86 MAPKKK protein encoded by 73 MAPKKK genes in Brachypodium. Phylogenetic analysis of MAPKKK family from Arabidopsis, rice, and Brachypodium has classified them into three subfamilies, of which 28 belonged to MEKK, 52 to Raf, and 6 to ZIK subfamily, respectively. Conserved protein motif, exon-intron organization, and splicing intron phase in kinase domains supported the evolutionary relationships inferred from the phylogenetic analysis. And gene duplication analysis suggested the chromosomal segment duplication happened before the divergence of the rice and Brachypodium, while all of three tandem duplicated gene pairs happened after their divergence. We further demonstrated that the MAPKKKs have evolved under strong purifying selection, implying the conservation of them. The splicing transcripts expression analysis showed that the splicesome translating longest protein tended to be adopted. Furthermore, the expression analysis of BdMAPKKKs in different organs and development stages as well as heat, virus and drought stresses revealed that the MAPKKK genes were involved in various signaling pathways. And the circadian analysis suggested there were 41 MAPKKK genes in Brachypodium showing cycled expression in at least one condition, of which seven MAPKKK genes expressed in all conditions and the promoter analysis indicated these genes possessed many cis-acting regulatory elements involved in circadian and light response. Finally, the co-expression network of MAPK, MAPKK, and MAPKKK in Brachypodium was constructed using 144 microarray and RNA-seq datasets, and ten potential MAPK cascades pathway were predicted. To conclude, our study provided the important information for evolutionary and functional characterization of MAPKKK family in Brachypodium, which will facilitate the functional analysis of BdMAPKKK genes, and also will facilitate better understanding the MAPK signal pathway in Brachypodium and beyond.

Salt stress sensing and early signalling events in plant roots: Current knowledge and hypothesis

Soil salinity is a major environmental constraint to crop production. While the molecular identity and functional expression of Na(+) transport systems mediating Na(+) exclusion from the cytosol has been studied in detail, far less is known about the mechanisms by which plants sense high Na(+) levels in the soil and the rapid signalling events that optimise plant performance under saline conditions. This review aims to fill this gap. We first discuss the nature of putative salt stress sensors, candidates which include Na(+) transport systems, mechanosensory proteins, proteins with regulatory Na(+) binding sites, sensing mediated by cyclic nucleotide-gated channels, purine receptors, annexin and voltage gating. We suggest that several transport proteins may be clustered together to form a microdomain in a lipid raft, allowing rapid changes in the activity of an individual protein to be translated into stress-induced Ca(2+) and H2O2 signatures. The pathways of stress signalling to downstream targets are discussed, and the kinetics and specificity of salt stress signalling between glycophytes and halophytes is compared. We argue that these sensing mechanisms operate in parallel, providing plants with a robust system for decoding information about the specific nature and severity of the imposed salt stress.

OsMAPK6, a mitogen-activated protein kinase, influences rice grain size and biomass production

Grain size is an important agronomic trait in determining grain yield. However, the molecular mechanisms that determine the final grain size are not well understood. Here, we report the functional analysis of a rice (Oryza sativa L.) mutant, dwarf and small grain1 (dsg1), which displays pleiotropic phenotypes, including small grains, dwarfism and erect leaves. Cytological observations revealed that the small grain and dwarfism of dsg1 were mainly caused by the inhibition of cell proliferation. Map-based cloning revealed that DSG1 encoded a mitogen-activated protein kinase (MAPK), OsMAPK6. OsMAPK6 was mainly located in the nucleus and cytoplasm, and was ubiquitously distributed in various organs, predominately in spikelets and spikelet hulls, consistent with its role in grain size and biomass production. As a functional kinase, OsMAPK6 interacts strongly with OsMKK4, indicating that OsMKK4 is likely to be the upstream MAPK kinase of OsMAPK6 in rice. In addition, hormone sensitivity tests indicated that the dsg1 mutant was less sensitive to brassinosteroids (BRs). The endogenous BR levels were reduced in dsg1, and the expression of several BR signaling pathway genes and feedback-inhibited genes was altered in the dsg1 mutant, with or without exogenous BRs, indicating that OsMAPK6 may contribute to influence BR homeostasis and signaling. Thus, OsMAPK6, a MAPK, plays a pivotal role in grain size in rice, via cell proliferation, and BR signaling and homeostasis.

Signaling mechanisms in pattern-triggered immunity (PTI)

In nature, plants constantly have to face pathogen attacks. However, plant disease rarely occurs due to efficient immune systems possessed by the host plants. Pathogens are perceived by two different recognition systems that initiate the so-called pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), both of which are accompanied by a set of induced defenses that usually repel pathogen attacks. Here we discuss the complex network of signaling pathways occurring during PTI, focusing on the involvement of mitogen-activated protein kinases.

The pearl millet mitogen-activated protein kinase PgMPK4 is involved in responses to downy mildew infection and in jasmonic- and salicylic acid-mediated defense

Plant mitogen-activated protein kinases (MPKs) transduce signals required for the induction of immunity triggered by host recognition of pathogen-associated molecular patterns. We isolated a full-length cDNA of a group B MPK (PgMPK4) from pearl millet. Autophosphorylation assay of recombinant PgMPK4 produced in Escherichia coli confirmed it as a kinase. Differential accumulation of PgMPK4 mRNA and kinase activity was observed between pearl millet cultivars 852B and IP18292 in response to inoculation with the downy mildew oomycete pathogen Sclerospora graminicola. This increased accumulation of PgMPK4 mRNA, kinase activity as well as nuclear-localization of PgMPK protein(s) was only detected in the S. graminicola resistant cultivar IP18292 with a ~tenfold peak at 9 h post inoculation. In the susceptible cultivar 852B, PgMPK4 mRNA and immuno-detectable nuclear PgMPK could be induced by application of the chemical elicitor β-amino butyric acid, the non-pathogenic bacteria Pseudomonas fluorescens, or by the phytohormones jasmonic acid (JA) or salicylic acid (SA). Furthermore, kinase inhibitor treatments indicated that PgMPK4 is involved in the JA- and SA-mediated expression of three defense genes, lipoxygenase, catalase 3 and polygalacturonase-inhibitor protein. These findings indicate that PgMPK/s contribute to pearl millet defense against the downy mildew pathogen by activating the expression of defense proteins.

Chitosan-induced antiviral activity and innate immunity in plants

Immunity represents a trait common to all living organisms, and animals and plants share some similarities. Therefore, in susceptible host plants, complex defence machinery may be stimulated by elicitors. Among these, chitosan deserves particular attention because of its proved efficacy. This survey deals with the antiviral activity of chitosan, focusing on its perception by the plant cell and mechanism of action. Emphasis has been paid to benefits and limitations of this strategy in crop protection, as well as to the potential of chitosan as a promising agent in virus disease control.

Capsicum annuum transcription factor WRKYa positively regulates defense response upon TMV infection and is a substrate of CaMK1 and CaMK2

Plants are constantly exposed to pathogens and environmental stresses. To minimize damage caused by these potentially harmful factors, plants respond by massive transcriptional reprogramming of various stress-related genes via major transcription factor families. One of the transcription factor families, WRKY, plays an important role in diverse stress response of plants and is often useful to generate genetically engineered crop plants. In this study, we carried out functional characterization of CaWRKYa encoding group I WRKY member, which is induced during hypersensitive response (HR) in hot pepper (Capsicum annuum) upon Tobacco mosaic virus (TMV) infection. CaWRKYa was involved in L-mediated resistance via transcriptional reprogramming of pathogenesis-related (PR) gene expression and affected HR upon TMV-P₀ infection. CaWRKYa acts as a positive regulator of this defense system and could bind to the W-box of diverse PR genes promoters. Furthermore, we found Capsicum annuum mitogen-activated protein kinase 1 (CaMK1) and 2 (CaMK2) interacted with CaWRKYa and phosphorylated the SP clusters but not the MAPK docking (D)-domain of CaWRKYa. Thus, these results demonstrated that CaWRKYa was regulated by CaMK1 and CaMK2 at the posttranslational level in hot pepper.

Mitogen-activated protein kinase cascades in Vitis vinifera

Protein phosphorylation is one of the most important mechanisms to control cellular functions in response to external and endogenous signals. Mitogen-activated protein kinases (MAPK) are universal signaling molecules in eukaryotes that mediate the intracellular transmission of extracellular signals resulting in the induction of appropriate cellular responses. MAPK cascades are composed of four protein kinase modules: MAPKKK kinases (MAPKKKKs), MAPKK kinases (MAPKKKs), MAPK kinases (MAPKKs), and MAPKs. In plants, MAPKs are activated in response to abiotic stresses, wounding, and hormones, and during plant pathogen interactions and cell division. In this report, we performed a complete inventory of MAPK cascades genes in Vitis vinifera, the whole genome of which has been sequenced. By comparison with MAPK, MAPK kinases, MAPK kinase kinases and MAPK kinase kinase kinase kinase members of Arabidopsis thaliana, we revealed the existence of 14 MAPKs, 5 MAPKKs, 62 MAPKKKs, and 7 MAPKKKKs in Vitis vinifera. We identified orthologs of V. vinifera putative MAPKs in different species, and ESTs corresponding to members of MAPK cascades in various tissues. This work represents the first complete inventory of MAPK cascades in V. vinifera and could help elucidate the biological and physiological functions of these proteins in V. vinifera.

Genome-wide identification of mitogen-activated protein kinase gene family in Gossypium raimondii and the function of their corresponding orthologs in tetraploid cultivated cotton

BACKGROUND

Mitogen-activated protein kinase (MAPK) cascades play a crucial role in plant growth and development as well as biotic and abiotic stress responses. Knowledge about the MAPK gene family in cotton is limited, and systematic investigation of MAPK family proteins has not been reported.

RESULTS

By performing a bioinformatics homology search, we identified 28 putative MAPK genes in the Gossypium raimondii genome. These MAPK members were anchored onto 11 chromosomes in G. raimondii, with uneven distribution. Phylogenetic analysis showed that the MAPK candidates could be classified into the four known A, B, C and D groups, with more MAPKs containing the TEY phosphorylation site (18 members) than the TDY motif (10 members). Furthermore, 21 cDNA sequences of MAPKs with complete open reading frames (ORFs) were identified in G. hirsutum via PCR-based approaches, including 13 novel MAPKs and eight with homologs reported previously in tetraploid cotton. The expression patterns of 23 MAPK genes reveal their important roles in diverse functions in cotton, in both various developmental stages of vegetative and reproductive growth and in the stress response. Using a reverse genetics approach based on tobacco rattle virus-induced gene silencing (TRV-VIGS), we further verified that MPK9, MPK13 and MPK25 confer resistance to defoliating isolates of Verticillium dahliae in cotton. Silencing of MPK9, MPK13 and MPK25 can significantly enhance cotton susceptibility to this pathogen.

CONCLUSIONS

This study presents a comprehensive identification of 28 mitogen-activated protein kinase genes in G. raimondii. Their phylogenetic relationships, transcript expression patterns and responses to various stressors were verified. This study provides the first systematic analysis of MAPKs in cotton, improving our understanding of defense responses in general and laying the foundation for future crop improvement using MAPKs.

Green leaf volatiles, fire and nonanoic acid activate MAPkinases in the model grass species Lolium temulentum

Background

Previously it has been shown that mechanical wounding, salinity and heat activated a 46 kDa and 44 kDa mitogen-activated protein kinases (MAPKs) in forage related grasses. Forage and turf related grasses are utilized in diverse environments where they are routinely subjected to herbicides and exposed to fire and volatiles after cutting, however very little is known concerning the perception or molecular responses to these different stresses or compounds.

Results

In the model grass species Lolium temulentum (Lt), a 46 kDa mitogen-activated protein kinase (MAPK) was activated in the leaves within 5 min and a 44 kDa MAPK 15 min after exposure to green leaf volatiles released from grass clippings. When the tips of leaves of Lt plants were scorched by fire, the 46 kDa MAPK and 44 kDa MAPK were rapidly activated within 5 min and 20 min respectively in the treated leaf, and 15 min systemically in an adjacent untreated tiller after exposure to fire. Nonanoic acid (pelargonic acid), a component in herbicides used on grasses, activated a 46 kDa MAPK in the treated leaves within 5 min of exposure and 15 min in systemic tissues. At concentrations normally used in the herbicides, nonanoic acid was found to only weakly activate the 44 kDa MAPK after an hour in treated leaves, but strongly activated it in the systemic tillers 30 min after treatment. Acetic acid, HCl and NaOH also were found to activate these MAPKs in treated tillers.

Conclusion

The rapid activation of these MAPKs to a wide range of stress stimuli, suggest that these MAPKs play a role in the perception and response to these stresses and compounds. The activation of the MAPK by green leaf volatiles indicates a role for these compounds in wound signaling in grasses.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-0500-7-807) contains supplementary material, which is available to authorized users.

Protein interactome analysis of 12 mitogen-activated protein kinase kinase kinase in rice using a yeast two-hybrid system

The mitogen-activated protein kinase (MAPK) cascade is composed at least of MAP3K (for MAPK kinase kinase), MAP2K, and MAPK family modules. These components together play a central role in mediating extracellular signals to the cell and vice versa by interacting with their partner proteins. However, the MAP3K-interacting proteins remain poorly investigated in plants. Here, we utilized a yeast two-hybrid system and bimolecular fluorescence complementation in the model crop rice (Oryza sativa) to map MAP3K-interacting proteins. We identified 12 novel nonredundant interacting protein pairs (IPPs) representing 11 nonredundant interactors using 12 rice MAP3Ks (available as full-length cDNA in the rice KOME (http://cdna01.dna.affrc.go.jp/cDNA/) at the time of experimental design and execution) as bait and a rice seedling cDNA library as prey. Of the 12 MAP3Ks, only six had interacting protein partners. The established MAP3K interactome consisted of two kinases, three proteases, two forkhead-associated domain-containing proteins, two expressed proteins, one E3 ligase, one regulatory protein, and one retrotransposon protein. Notably, no MAP3K showed physical interaction with either MAP2K or MAPK. Seven IPPs (58.3%) were confirmed in vivo by bimolecular fluorescence complementation. Subcellular localization of 14 interactors, together involved in nine IPPs (75%) further provide prerequisite for biological significance of the IPPs. Furthermore, GO of identified interactors predicted their involvement in diverse physiological responses, which were supported by a literature survey. These findings increase our knowledge of the MAP3K-interacting proteins, help in proposing a model of MAPK modules, provide a valuable resource for developing a complete map of the rice MAPK interactome, and allow discussion for translating the interactome knowledge to rice crop improvement against environmental factors.

Precise spatio-temporal modulation of ACC synthase by MPK6 cascade mediates the response of rose flowers to rehydration

Drought is a major abiotic stress that affects the development and growth of most plants, and limits crop yield worldwide. Although the response of plants to drought has been well documented, much less is known about how plants respond to the water recovery process, namely rehydration. Here, we describe the spatio-temporal response of plant reproductive organs to rehydration using rose flowers as an experimental system. We found that rehydration triggered rapid and transient ethylene production in the gynoecia. This ethylene burst serves as a signal to ensure water recovery in flowers, and promotes flower opening by influencing the expression of a set of rehydration-responsive genes. An in-gel kinase assay suggested that the rehydration-induced ethylene burst resulted from transient accumulation of RhACS1/2 proteins in gynoecia. Meanwhile, RhMPK6, a rose homolog of Arabidopsis thaliana MPK6, is rapidly activated by rehydration within 0.5 h. Furthermore, RhMPK6 was able to phosphorylate RhACS1 but not RhACS2 in vitro. Application of the kinase inhibitor K252a suppressed RhACS1 accumulation and rehydration-induced ethylene production in gynoecia, and the protein phosphatase inhibitor okadaic acid had the opposite effect, confirming that accumulation of RhACS1 was phosphorylation-dependent. Finally, silencing of RhMPK6 significantly reduced ethylene production in gynoecia when flowers were subjected to rehydration. Taken together, our results suggest that temporal- and spatial-specific activation of an RhMPK6-RhACS1 cascade is responsible for rehydration-induced ethylene production in gynoecia, and that the resulting ethylene-mediated signaling pathway is a key factor in flower rehydration.

Genome-wide identification and analysis of mitogen activated protein kinase kinase kinase gene family in grapevine (Vitis vinifera)

BACKGROUND

Mitogen-activated protein kinase kinase kinases (MAPKKKs; MAP3Ks) are important components of MAPK cascades, which are highly conserved signal transduction pathways in animals, yeast and plants, play important roles in plant growth and development. MAPKKKs have been investigated on their evolution and expression patterns in limited plants including Arabidopsis, rice and maize.

RESULTS

In this study, we performed a genome-wide survey and identified 45 MAPKKK genes in the grapevine genome. Chromosome location, phylogeny, gene structure and conserved protein motifs of MAPKKK family in grapevine have been analyzed to support the prediction of these genes. In the phylogenetic analysis, MAPKKK genes of grapevine have been classified into three subgroups as described for Arabidopsis, named MEKK, ZIK and RAF, also confirmed in grapevine by the analysis of conserved motifs and exon-intron organizations. By analyzing expression profiles of MAPKKK genes in grapevine microarray databases, we highlighted the modulation of different MAPKKKs in different organs and distinct developmental stages. Furthermore, we experimentally investigated the expression profiles of 45 grape MAPKKK genes in response to biotic (powdery mildew) and abiotic stress (drought), as well as to hormone (salicylic acid, ethylene) and hydrogen peroxide treatments, and identified several candidate MAPKKK genes that might play an important role in biotic and abiotic responses in grapevine, for further functional characterization.

CONCLUSIONS

This is the first comprehensive experimental survey of the grapevine MAPKKK gene family, which provides insights into their potential roles in regulating responses to biotic and abiotic stresses, and the evolutionary expansion of MAPKKKs is associated with the diverse requirement in transducing external and internal signals into intracellular actions in MAPK cascade in grapevine.

A mitogen-activated protein kinase cascade module, MKK3-MPK6 and MYC2, is involved in blue light-mediated seedling development in Arabidopsis

Mitogen-activated protein kinase (MAPK) pathways are involved in several signal transduction processes in eukaryotes. Light signal transduction pathways have been extensively studied in plants; however, the connection between MAPK and light signaling pathways is currently unknown. Here, we show that MKK3-MPK6 is activated by blue light in a MYC2-dependent manner. MPK6 physically interacts with and phosphorylates a basic helix-loop-helix transcription factor, MYC2, and is phosphorylated by a MAPK kinase, MKK3. Furthermore, MYC2 binds to the MPK6 promoter and regulates its expression in a feedback regulatory mechanism in blue light signaling. We present mutational and physiological studies that illustrate the function of the MKK3-MPK6-MYC2 module in Arabidopsis thaliana seedling development and provide a revised mechanistic view of photomorphogenesis.