GhMPK16, a novel stress-responsive group D MAPK gene from cotton, is involved in disease resistance and drought sensitivity

GhMPK9-GhRAF39_1-GhWRKY40a Regulates the GhERF1b- and GhABF2-Mediated Pathways to Increase Cotton Disease Resistance

Mitogen-activated protein kinase (MAPK) cascade is the center of plant signal transduction system that amplify immune signals into cellular responses by phosphorylating diverse substrates. The MAPK cascade consisting of MAPK kinase kinases (MAPKKKs), MAPK kinases (MAPKKs), and MAPKs is well characterized in plants, in which Raf-like kinases are generally regarded as MAPKKKs. However, it is rarely reported that Raf-like MAPKKKs function as middle regulators to link MAPK and its downstream transcription factors in plant immunity. Verticillium wilt, caused by the soil-borne vascular fungus Verticillium dahliae, is a serious disease in many plants, including cotton. The previous studies showed that GhMPK9 (a MAPK) is involved in the response to Verticillium wilt. Here, the Raf-like kinase GhRAF39_1 is reported as helper regulates the phosphorylation of WRKY transcription factor GhWRKY40a by GhMPK9. The phosphorylated GhWRKY40a can further activate the transcription of GhERF1b to up-regulate defense-related genes while inhibit the transcription of GhABF2 to regulate the stomatal opening, thus improving the resistance to Verticillium wilt in cotton. This study reveals a new signaling module of GhMPK9-GhRAF39_1-GhWRKY40a to regulate GhERF1b- and GhABF2-mediated defense responses, which triggers plant defense against Verticillium wilt.

Crosstalk and trade-offs: Plant responses to climate change-associated abiotic and biotic stresses

As sessile organisms, plants are constantly challenged by a dynamic growing environment. This includes fluctuations in temperature, water availability, light levels, and changes in atmospheric constituents such as carbon dioxide (CO2 ) and ozone (O3 ). In concert with changes in abiotic conditions, plants experience changes in biotic stress pressures, including plant pathogens and herbivores. Human-induced increases in atmospheric CO2 levels have led to alterations in plant growth environments that impact their productivity and nutritional quality. Additionally, it is predicted that climate change will alter the prevalence and virulence of plant pathogens, further challenging plant growth. A knowledge gap exists in the complex interplay between plant responses to biotic and abiotic stress conditions. Closing this gap is crucial for developing climate resilient crops in the future. Here, we briefly review the physiological responses of plants to elevated CO2 , temperature, tropospheric O3 , and drought conditions, as well as the interaction of these abiotic stress factors with plant pathogen pressure. Additionally, we describe the crosstalk and trade-offs involved in plant responses to both abiotic and biotic stress, and outline targets for future work to develop a more sustainable future food supply considering future climate change.

PeMPK17 interacts with PeMKK7 and participates in para-hydroxybenzoic acid stress resistance by removing reactive oxygen species

Mitogen-activated protein kinase (MAPK) plays a crucial role in plant stress response. Poplar is one of the most important afforestation and timber species and inevitably encounters allelopathy effects during continuous cropping. para-hydroxybenzoic acid (pHBA) is a primary soil allelochemical, which can restrict the growth and biomass of poplar. However, the involvement of MAPKs in the underlying physiological and molecular regulatory mechanisms in response to pHBA stress remains unclear. In this study, PeMPK17, a gene encoding a group D MAPK, was cloned from Populus × euramericana. PeMPK17 protein was localized in both nucleus and plasma membrane. Quantitative real-time polymerase chain reaction analysis demonstrated that PeMPK17 expression in poplar increased when treated with pHBA, PEG, and H₂O₂. Exogenous pHBA and H₂O₂ induced PeMPK17 expression mediated by reactive oxygen species (ROS). The transgenic poplar plants overexpressing PeMPK17 demonstrated attenuated phenotypic injury, higher relative water content in leaves, and lower ion leakage under pHBA stress. In transgenic poplar, the activity and expression of antioxidant enzymes including superoxide dismutase, peroxidase, and catalase increased, while the content of H₂O₂, O₂·^-, and malondialdehyde decreased. These results suggested that PeMPK17 protects cell membranes from oxidative damage by removing excess ROS. In addition, overexpression of PeMPK17 promoted osmoprotectant accumulation including soluble sugar and free proline, which may aid in the regulation of ROS balance under pHBA treatment. Furthermore, the interaction between PeMPK17 and PeMKK7 was confirmed. Collectively, these data identify the molecular mechanisms and signal pathways associated with PeMPK17 that regulate pHBA response in poplar.

Revisiting the role of MAPK signalling pathway in plants and its manipulation for crop improvement

The mitogen-activated protein kinase (MAPK) pathway is an important signalling event associated with every aspect of plant growth, development, yield, abiotic and biotic stress adaptation. Being a central metabolic pathway, it is a vital target for manipulation for crop improvement. In this review, we have summarised recent advancements in understanding involvement of MAPK signalling in modulating abiotic and biotic stress tolerance, architecture and yield of plants. MAPK signalling cross talks with reactive oxygen species (ROS) and abscisic acid (ABA) signalling events in bringing about abiotic stress adaptation in plants. The intricate involvement of MAPK pathway with plant's pathogen defence ability has also been identified. Further, recent research findings point towards participation of MAPK signalling in shaping plant architecture and yield. These make MAPK pathway an important target for crop improvement and we discuss here various strategies to tweak MAPK signalling components for designing future crops with improved physiology and phenotypes.

Harnessing the role of mitogen-activated protein kinases against abiotic stresses in plants

Crop plants are vulnerable to various biotic and abiotic stresses, whereas plants tend to retain their physiological mechanisms by evolving cellular regulation. To mitigate the adverse effects of abiotic stresses, many defense mechanisms are induced in plants. One of these mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used in the transduction of extracellular stimuli into intercellular responses. This stress signaling pathway is activated by a series of responses involving MAPKKKs→MAPKKs→MAPKs, consisting of interacting proteins, and their functions depend on the collaboration and activation of one another by phosphorylation. These proteins are key regulators of MAPK in various crop plants under abiotic stress conditions and also related to hormonal responses. It is revealed that in response to stress signaling, MAPKs are characterized as multigenic families and elaborate the specific stimuli transformation as well as the antioxidant regulation system. This pathway is directed by the framework of proteins and stopping domains confer the related associates with unique structure and functions. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in plants, such as Arbodiposis, tomato, potato, alfalfa, poplar, rice, wheat, maize, and apple. In this review, we summarized the recent work on MAPK response to abiotic stress and the classification of MAPK cascade in crop plants. Moreover, we highlighted the modern research methodologies such as transcriptomics, proteomics, CRISPR/Cas technology, and epigenetic studies, which proposed, identified, and characterized the novel genes associated with MAPKs and their role in plants under abiotic stress conditions. In-silico-based identification of novel MAPK genes also facilitates future research on MAPK cascade identification and function in crop plants under various stress conditions.

Genome Identification of the Tea Plant (Camellia sinensis) ASMT Gene Family and Its Expression Analysis under Abiotic Stress

The tea plant (Camellia sinensis (L.) O. Ktze) is an important cash crop grown worldwide. It is often subjected to environmental stresses that influence the quality and yield of its leaves. Acetylserotonin-O-methyltransferase (ASMT) is a key enzyme in melatonin biosynthesis, and it plays a critical role in plant stress responses. In this paper, a total of 20 ASMT genes were identified in tea plants and classified into three subfamilies based on a phylogenetic clustering analysis. The genes were unevenly distributed on seven chromosomes; two pairs of genes showed fragment duplication. A gene sequence analysis showed that the structures of the ASMT genes in the tea plants were highly conserved and that the gene structures and motif distributions slightly differed among the different subfamily members. A transcriptome analysis showed that most CsASMT genes did not respond to drought and cold stresses, and a qRT-PCR analysis showed that CsASMT08, CsASMT09, CsASMT10, and CsASMT20 significantly responded to drought and low-temperature stresses; in particular, CsASMT08 and CsASMT10 were highly expressed under low-temperature stress and negatively regulated in response to drought stress. A combined analysis revealed that CsASMT08 and CsASMT10 were highly expressed and that their expressions differed before and after treatment, which indicates that they are potential regulators of abiotic stress resistance in the tea plant. Our results can facilitate further studies on the functional properties of CsASMT genes in melatonin synthesis and abiotic stress in the tea plant.

Systematic analysis of Histidine photosphoto transfer gene family in cotton and functional characterization in response to salt and around tolerance

BACKGROUND

Phosphorylation regulated by the two-component system (TCS) is a very important approach signal transduction in most of living organisms. Histidine phosphotransfer (HP) is one of the important members of the TCS system. Members of the HP gene family have implications in plant stresses tolerance and have been deeply studied in several crops. However, upland cotton is still lacking with complete systematic examination of the HP gene family.

RESULTS

A total of 103 HP gene family members were identified. Multiple sequence alignment and phylogeny of HPs distributed them into 7 clades that contain the highly conserved amino acid residue "XHQXKGSSXS", similar to the Arabidopsis HP protein. Gene duplication relationship showed the expansion of HP gene family being subjected with whole-genome duplication (WGD) in cotton. Varying expression profiles of HPs illustrates their multiple roles under altering environments particularly the abiotic stresses. Analysis is of transcriptome data signifies the important roles played by HP genes against abiotic stresses. Moreover, protein regulatory network analysis and VIGS mediated functional approaches of two HP genes (GhHP23 and GhHP27) supports their predictor roles in salt and drought stress tolerance.

CONCLUSIONS

This study provides new bases for systematic examination of HP genes in upland cotton, which formulated the genetic makeup for their future survey and examination of their potential use in cotton production.

Arbuscular mycorrhizal fungi enhance photosynthesis and drought tolerance by regulating MAPK genes expressions of Populus simonii × P. nigra

Arbuscular mycorrhizal fungi (AMF) promote plants to absorb more water and nutrients and improve their stress resistance. As the main signal transducer, the mitogen-activated protein kinase (MAPK) cascade plays a vital role in drought stress. However, how the MAPK family genes of mycorrhizal plants respond to stress is still not clear. Our study analyzed physiological indexes and expression profiles of MAPK family genes of Populus simonii × P. nigra under two inoculation treatments (inoculated with or without Rhizophagus irregularis) and two water conditions (well-watered or drought stress). The results showed that the stronger photosynthesis of mycorrhizal plants may be mediated by MAPK genes induced by AMF. Mycorrhizal plants showed lower oxidative damage and drought sensitivity. Mycorrhiza downregulated the expression of PsnMAPK7-2, PsnMAPK16-1, PsnMAPK19-2, and PsnMAPK20-2 which negatively regulate drought tolerance and induced specific PsnMAPKs in roots which activate transcription factors to regulate downstream gene expressions, enhancing drought tolerance. This is the first time to identify part of the MAPK gene family of P. simonii × P. nigra at the genome level and study MAPK genes in mycorrhizal forest trees. This is helpful to understand the function of the MAPK gene family in response to drought of mycorrhizal plants and lays a foundation for afforestation by using mycorrhizal saplings.

Defense Mechanisms of Cotton Fusarium and Verticillium Wilt and Comparison of Pathogenic Response in Cotton and Humans

Cotton is an important economic crop. Fusarium and Verticillium are the primary pathogenic fungi that threaten both the quality and sustainable production of cotton. As an opportunistic pathogen, Fusarium causes various human diseases, including fungal keratitis, which is the most common. Therefore, there is an urgent need to study and clarify the resistance mechanisms of cotton and humans toward Fusarium in order to mitigate, or eliminate, its harm. Herein, we first discuss the resistance and susceptibility mechanisms of cotton to Fusarium and Verticillium wilt and classify associated genes based on their functions. We then outline the characteristics and pathogenicity of Fusarium and describe the multiple roles of human neutrophils in limiting hyphal growth. Finally, we comprehensively compare the similarities and differences between animal and plant resistance to Fusarium and put forward new insights into novel strategies for cotton disease resistance breeding and treatment of Fusarium infection in humans.

Transcriptomic Analysis to Unravel Potential Pathways and Genes Involved in Pecan (Carya illinoinensis) Resistance to Pestalotiopsis microspora

Fruit black spot (FBS), a fungal disease of pecan (Carya illinoinensis (Wangenh) K. Koch) caused by the pathogen Pestalotiopsis microspora, is a serious disease and poses a critical threat to pecan yield and quality. However, the details of pecan responses to FBS infection at the transcriptional level remain to be elucidated. In present study, we used RNA-Seq to analyze differential gene expression in three pecan cultivars with varied resistance to FBS infection: Xinxuan-4 (X4), Mahan (M), and Wichita (W), which were categorized as having low, mild, and high susceptibility to FBS, respectively. Nine RNA-Seq libraries were constructed, comprising a total of 58.56 Gb of high-quality bases, and 2420, 4380, and 8754 differentially expressed genes (DEGs) with |log2Fold change| ≥ 1 and p-value < 0.05 were identified between M vs. X4, W vs. M, and W vs. X4, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway analyses were performed to further annotate DEGs that were part of specific pathways, which revealed that out of 134 total pathways, MAPK signaling pathway, plant−pathogen interaction, and plant hormone signal transduction were highly enriched. Transcriptomic profiling analysis revealed that 1681 pathogen-related genes (PRGs), including 24 genes encoding WRKY transcription factors, potentially participate in the process of defense against Pestalotiopsis microspora infection in pecan. The correlation of WRKY TFs and PRGs was also performed to reveal the potential interaction networks among disease-resistance/pathogenesis-related genes and WRKY TFs. Expression profiling of nine genes annotated as TIFY, WRKY TF, and disease-resistance protein-related genes was performed using qRT-PCR, and the results were correlated with RNA-Seq data. This study provides valuable information on the molecular basis of pecan−Pestalotiopsis microspora interaction mechanisms and offers a repertoire of candidate genes related to pecan fruit response to FBS infection.

Characterization of walnut JrWOX11 and its overexpression provide insights into adventitious root formation and development and abiotic stress tolerance

The well-developed root system enables plant survival under various environmental stresses. WUSCHEL-RELATED HOMEOBOX GENE 11 (WOX11) plays a critical role in adventitious root formation and development in rice, Arabidopsis, and easy-to-root tree poplar. However, in difficult-to-root trees, the knowledge of WOX11 during adventitious root formation and development remains scarce. In this study, the JrWOX11 gene was isolated from a difficult-to-root tree walnut and heterologously expressed in the "84K" poplar. The results showed that JrWOX11 contained a similar structure and sequence to the homologous genes in rice, Arabidopsis, and poplar, but had different numbers and types of motifs and cis-elements. JrWOX11 lacked the motif GGAIQY compared to that in easy-to-root trees. In addition, JrWOX11 expression was induced by ABA, PEG, and NaCl treatments. Overexpression of JrWOX11 in poplar promoted root initiation and significantly increased adventitious root (ARs) number, lateral roots (LRs) number, and root hair (RH) length. Furthermore, the aboveground biomass was notably increased under NaCl and PEG treatments in transgenic plants. When NaCl and PEG were removed, the survival rate, aerial shoot development, and de novo root organogenesis were also markedly enhanced in transgenic shoot cuttings. The study provides valuable information on the differences between JrWOX11 and the homologous genes in rice, Arabidopsis, and poplar, and supports the critical role of JrWOX11 in the formation of AR and tolerance to salt and osmotic stresses.

Impact of water deficiency on leaf cuticle lipids and gene expression networks in cotton (Gossypium hirsutum L.)

BACKGROUND

Water deficit (WD) has serious effect on the productivity of crops. Formation of cuticular layer with increased content of wax and cutin on leaf surfaces is closely related to drought tolerance. Identification of drought tolerance associated wax components and cutin monomers and the genes responsible for their biosynthesis is essential for understanding the physiological and genetic mechanisms underlying drought tolerance and improving crop drought resistance.

RESULT

In this study, we conducted comparative phenotypic and transcriptomic analyses of two Gossypium hirsutum varieties that are tolerant (XL22) or sensitive (XL17) to drought stress. XL17 consumed more water than XL22, particularly under the WD conditions. WD significantly induced accumulation of most major wax components (C29 and C31 alkanes) and cutin monomers (palmitic acid and stearic acid) in leaves of both XL22 and XL17, although accumulation of the major cutin monomers, i.e., polyunsaturated linolenic acid (C18:3n-3) and linoleic acid (C18:2n-6), were significantly repressed by WD in both XL22 and XL17. According to the results of transcriptome analysis, although many genes and their related pathways were commonly induced or repressed by WD in both XL22 and XL17, WD-induced differentially expressed genes specific to XL22 or XL17 were also evident. Among the genes that were commonly induced by WD were the GhCER1 genes involved in biosynthesis of alkanes, consistent with the observation of enhanced accumulation of alkanes in cotton leaves under the WD conditions. Interestingly, under the WD conditions, several GhCYP86 genes, which encode enzymes catalyzing the omega-hydroxylation of fatty acids and were identified to be the hub genes of one of the co-expression gene modules, showed a different expression pattern between XL22 and XL17 that was in agreement with the WD-induced changes of the content of hydroxyacids or fatty alcohols in these two varieties.

CONCLUSION

The results contribute to our comprehending the physiological and genetic mechanisms underlying drought tolerance and provide possible solutions for the difference of drought resistance of different cotton varieties.

Expression profiling of the mitogen-activated protein kinase gene family reveals their diverse response pattern in two different salt-tolerant Glycyrrhiza species

BACKGROUND

Mitogen-activated protein kinases (MPKs) play important role in response to environmental stress as crucial signal receptors or sensors. Our previous study indicated that salt stress acts as a positive factor to stimulate the production of pharmacodynamic metabolites in the medicinal plant Glycyrrhiza uralensis. Currently, little is known about the MPK gene family and their functions in the medicinal plant G. uralensis.

OBJECTIVE

Identification, comprehensive bioinformatic analysis, expression profiling, and response pattern under salt stress of the G. uralensis GuMPK gene family.

METHODS

Genome-wide investigation and expression profiling of the MPK gene family in G. uralensis, and their phylogenetic relationships, evolutionary characteristics, gene structure, motif distribution, promoter cis-acting element, and expression pattern under salt stress in two different salt-tolerant Glycyrrhiza species were performed.

RESULTS

A total of 20 G. uralensis GuMPK genes were identified and categorized into five groups, and had conserved gene structure and motif distribution. Expression profiling of GuMPK genes suggested their potentially diverse functions in plant growth and in response to phytohormones and environmental stress, particularly GuMPK1, 2, 5, and 10 as key components for G. uralensis in response to abiotic stress. Further expression analysis under NaCl treatment in two different salt-tolerant Glycyrrhiza species displayed the MPKs' different response patterns, emphasizing the role of MPK2, 5, 7, and 16 as potentially crucial genes for Glycyrrhiza to respond to salt stress.

CONCLUSION

Our results provide a genome-wide identification and expression profiling of MPK gene family in G. uralensis, and establish the foundation for screening key responsive genes and understanding the potential function and regulatory mechanism of GuMPKs in salt responsiveness.

Comprehensive analysis of MAPK cascade genes in sorghum (Sorghum bicolor L.) reveals SbMPK14 as a potential target for drought sensitivity regulation

The mitogen-activated protein kinase (MAPK) cascade plays a crucial role in regulating many important biological processes in plants. Here, we identified and characterized eight MAPKK and 49 MAPKKK genes in sorghum and analyzed their differential expression under drought treatment; we also characterized 16 sorghum MAPK genes. RNA-seq analysis revealed that 10 MAPK cascade genes were involved in drought stress response at the transcriptome level in sorghum. Overexpression of SbMPK14 in Arabidopsis and maize resulted in hypersensitivity to drought by promoting water loss, indicating that SbMPK14 functions as a negative regulator of the drought response. Subsequent transcriptome analysis and qRT-PCR verification of maize SbMPK14 overexpression lines revealed that SbMPK14 likely increases plant drought sensitivity by suppressing the activity of specific ERF and WRKY transcription factors. This comprehensive study provides valuable insight into the mechanistic basis of MAPK cascade gene function and their responses to drought in sorghum.

Protein Kinase Signaling Pathways in Plant-Colletotrichum Interaction

Anthracnose is a fungal disease caused by members of Colletotrichum that affect a wide range of crop plants. Strategies to improve crop resistance are needed to reduce the yield losses; and one strategy is to manipulate protein kinases that catalyze reversible phosphorylation of proteins regulating both plant immune responses and fungal pathogenesis. Hence, in this review, we present a summary of the current knowledge of protein kinase signaling pathways in plant-Colletotrichum interaction as well as the relation to a more general understanding of protein kinases that contribute to plant immunity and pathogen virulence. We highlight the potential of combining genomic resources and phosphoproteomics research to unravel the key molecular components of plant-Colletotrichum interactions. Understanding the molecular interactions between plants and Colletotrichum would not only facilitate molecular breeding of resistant cultivars but also help the development of novel strategies for controlling the anthracnose disease.

Mitogen-activated protein kinase action in plant response to high-temperature stress: a mini review

In recent years, extreme weather events such as high temperature (HT) are becoming more frequent. HT has become one of the main environmental factors affecting crop growth and development. In nature, plant cells initiate corresponding tolerant mechanisms by sensing and transducing HT signals. The mitogen-activated protein kinase (MAPK) cascade is widely involved in the signal transduction of plants to various environmental stresses. MAPK-mediated HT responses have attracted more and more attention. We herein focus on the current state of knowledge of MAPK in the plant under HT stress and summarize the mechanisms of MAPK in HT response from Ca²⁺ signal, reactive oxygen species (ROS) signal, heat shock transcription factor and heat shock protein, antioxidant system, and the direct downstream targets of MAPK. This review encapsulates the known plant MAPK cascade and provides prospects for ongoing research on HT response.

Regulatory Network of Cotton Genes in Response to Salt, Drought and Wilt Diseases (Verticillium and Fusarium): Progress and Perspective

In environmental conditions, crop plants are extremely affected by multiple abiotic stresses including salinity, drought, heat, and cold, as well as several biotic stresses such as pests and pathogens. However, salinity, drought, and wilt diseases (e.g., Fusarium and Verticillium) are considered the most destructive environmental stresses to cotton plants. These cause severe growth interruption and yield loss of cotton. Since cotton crops are central contributors to total worldwide fiber production, and also important for oilseed crops, it is essential to improve stress tolerant cultivars to secure future sustainable crop production under adverse environments. Plants have evolved complex mechanisms to respond and acclimate to adverse stress conditions at both physiological and molecular levels. Recent progresses in molecular genetics have delivered new insights into the regulatory network system of plant genes, which generally includes defense of cell membranes and proteins, signaling cascades and transcriptional control, and ion uptake and transport and their relevant biochemical pathways and signal factors. In this review, we mainly summarize recent progress concerning several resistance-related genes of cotton plants in response to abiotic (salt and drought) and biotic (Fusarium and Verticillium wilt) stresses and classify them according to their molecular functions to better understand the genetic network. Moreover, this review proposes that studies of stress related genes will advance the security of cotton yield and production under a changing climate and that these genes should be incorporated in the development of cotton tolerant to salt, drought, and fungal wilt diseases (Verticillium and Fusarium).

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.

The Function of MAPK Cascades in Response to Various Stresses in Horticultural Plants

The mitogen-activated protein kinase (MAPK) cascade is a highly conserved signaling transduction module that transduces extracellular stimuli into intracellular responses in plants. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in horticultural plants, such as tomato and apple. Recent studies revealed that the MAPK cascade also plays crucial roles in the biotic and abiotic stress responses of horticultural plants. In this review, we summarize the composition and classification of MAPK cascades in horticultural plants and recent research on this cascade in responses to abiotic stresses (such as drought, extreme temperature and high salinity) and biotic stresses (such as pathogen infection). In addition, we discuss the most advanced research themes related to plant MAPK cascades, thus facilitating research on MAPK cascade functions in horticultural plants.

Chromosome-Level Reference Genome and Population Genomic Analysis Provide Insights into the Evolution and Improvement of Domesticated Mulberry (Morus alba)

Mulberry (Morus spp.) is the sole plant consumed by the domesticated silkworm. However, the genome of domesticated mulberry has not yet been sequenced, and the ploidy level of this species remains unclear. Here, we report a high-quality, chromosome-level domesticated mulberry (Morus alba) genome. Analysis of genomic data and karyotype analyses confirmed that M. alba is a diploid with 28 chromosomes (2n = 2x = 28). Population genomic analysis based on resequencing of 134 mulberry accessions classified domesticated mulberry into three geographical groups, namely, Taihu Basin of southeastern China (Hu mulberry), northern and southwestern China, and Japan. Hu mulberry had the lowest nucleotide diversity among these accessions and demonstrated obvious signatures of selection associated with environmental adaptation. Further phylogenetic analysis supports a previous proposal that multiple domesticated mulberry accessions previously classified as different species actually belong to one species. This study expands our understanding of genome evolution of the genus Morus and population structure of domesticated mulberry, which would facilitate mulberry breeding and improvement.

Screening of abiotic stress-responsive cotton genes using a cotton full-length cDNA overexpressing Arabidopsis library

Cotton (Gossypium hirsutum L.) is a major crop and the main source of natural fiber worldwide. Because various abiotic and biotic stresses strongly influence cotton fiber yield and quality, improved stress resistance of this crop plant is urgently needed. In this study, we used Gateway technology to construct a normalized full-length cDNA overexpressing (FOX) library from upland cotton cultivar ZM12 under various stress conditions. The library was transformed into Arabidopsis to produce a cotton-FOX-Arabidopsis library. Screening of this library yielded 6,830 transgenic Arabidopsis lines, of which 757 were selected for sequencing to ultimately obtain 659 cotton ESTs. GO and KEGG analyses mapped most of the cotton ESTs to plant biological process, cellular component, and molecular function categories. Next, 156 potential stress-responsive cotton genes were identified from the cotton-FOX-Arabidopsis library under drought, salt, ABA, and other stress conditions. Four stress-related genes identified from the library, designated as GhCAS, GhAPX, GhSDH, and GhPOD, were cloned from cotton complementary DNA, and their expression patterns under stress were analyzed. Phenotypic experiments indicated that overexpression of these cotton genes in Arabidopsis affected the response to abiotic stress. The method developed in this study lays a foundation for high-throughput cloning and rapid identification of cotton functional genes.

Plant hypersensitive response vs pathogen ingression: Death of few gives life to others

The hypersensitive response (HR) is a defense action against pathogen ingression. Typically, HR is predictable with the appearance of the dead, brown cells along with visible lesions. Although death during HR can be limited to the cells in direct contact with pathogens, yet cell death can also spread away from the infection site. The variety in morphologies of plant cell death proposes involvement of different pathways for triggering HR. It is considered that, despite the differences, HR in plants performs the resembling functions like that of animal programmed cell death (PCD) for confining pathogen progression. HR, in fact, crucially initiates systemic signals for activation of defense in distal plant parts that ultimately results in systemic acquired resistance (SAR). Therefore, HR can be separated from other local immune actions/responses at the infection site. HR comprises of serial events inclusive of transcriptional reprograming, Ca²⁺ influx, oxidative bursts and phyto-hormonal signaling. Although a lot of work has been done on HR in plants but many questions regarding mechanisms and consequences of HRs remain unaddressed.We have summarized the mechanistic roles and cellular events of plant cells during HR in defense regulation. Roles of different genes during HR have been discussed to clarify genetic control of HR in plants. Generally existing ambiguities about HR and programmed cell death at the reader level has been addressed.

Cloning, Genetic Transformation and Cellular Localization of Abiotic Stress Responsive Universal Stress Protein Gene (GUSP1) in Gossypium hirsutum

BACKGROUND

Drought stress seriously affects the cotton fiber development. Universal stress protein gene isolated from native species Gossypium arboreum has the promising tolerance role against these stresses.

OBJECTIVES

This study aimed to clone, characterize, and genetically transform the GUSP1 gene in local cotton and to observe its expression in transgenic plants under drought stress.

MATERIALS AND METHODS

Universal Stress Protein (GUSP1) gene from Gossypium arboreum was cloned in pCEMBIA (-) 1301plant expression vector by replacing Hygromycin and GUS exon with GUSP1-GFP fusion fragment. The construct was transformed into Agrobacterium tumefaciens and transient expression assay was confirmed by agro-infiltration of Nicotiana benthamiana leaves and green fluorescence under a confocal microscope. Gene integration and expression in transgenic plants was observed through Southern blot and real-time PCR analyses. Cellular localization was observed through a confocal microscope and the copy number of the transgene was observed in progeny plants.

RESULTS

Transformation efficiency was 1.9%. Developmental and spatial expression of GUSP1 was observed through Real-time PCR in stem, root, leaf, inflorescence, and seeds of transgenic plants at the vegetative and flowering stage. Integration of GUSP1 revealed a fragment of approximately 500 bp in Southern Blot analyses. Localization of GUSP1 was detected in the intact leaf of transgenic plants through GFP fluorescence in midrib, guard cells of stomata, and trichomes. Single gene copy was detected in the chromosome of transgenic seeds.

CONCLUSION

GUSP1 has cloned from native species of local cotton and its integration and expression in transgenic plants confirmed that the role of GUSP1 will provide direction to breed economically important cotton varieties.

Phytoremediation of petroleum-contaminated soil by Salicornia: from PSY activity to physiological and morphological communications

Petroleum is one of the critical environmental pollutants. Salicornia can grow in petroleum-contaminated soil. Therefore, the potential of two Iranian Salicornia species, S. persica Akhani and S. iranica Akhani, for phytoremediation of soils contaminated with 0.2% or 2% petroleum was evaluated over short (1 and 10 h) and long (100 days) periods of time. In addition, some key factors including the expression analysis of phytoene synthase, physiological and morphological factors were studied. Both species reduced the petroleum in 0.2% and 2% petroleum-contaminated soils to 40% and 60% of the initial amount, respectively. The expression of PSY increased twice more than the control 10 h after 0.2% petroleum stress and the carotenoid content increased twice more than the control. Chlorophyll a and total chlorophyll decreased three times less than the control in both contamination levels, while chlorophyll b decreased three times less than the control only in 2% contamination. The proline content peaked 10 h after 2% stress as it was 10 times more than the control. Promoter analysis of PSY showed the existence of responsive cis-acting elements to abscisic acid suggesting the key role of this gene in abiotic stresses.

Genome-wide analysis of the NF-Y gene family in peach (Prunus persica L.)

Background

Nuclear Factor Y (NF-Y) is a heterotrimeric complex composed of three unique subunits: NF-YA, NF-YB, and NF-YC. The NF-Y transcription factor complex binds to the CCAAT box of eukaryotic promoters, playing a vital role in various biological processes in plants. However, the NF-Y gene family has not yet been reported from the peach genome. The current study identified and classified candidate peach NF-Y genes for further functional analysis of this family.

Results

The current study identified 24 Nuclear Factor Y (NF-Y) transcription factor subunits (6 NF-YA, 12 NF-YB, and 6 NF-YC subunits) in peach. These NF-Y subunits were described with respect to basic physicochemical characteristics, chromosome locations, gene structures, and conserved domains. Based on an analysis of the phylogenetic relationships among peach NF-Ys, six pairs of paralogous NF-Ys were detected. The expansion of the peach NF-Y family occurred by segmental and tandem duplication. Phylogenetic gene synteny of NF-Y proteins was observed between peach and Arabidopsis, and five pairs of paralogous NF-Y proteins from peach and Arabidopsis were identified. Twenty-four peach NF-Ys displayed a diversity of tissue expression patterns. In addition, drought-responsive cis-elements were observed in peach NF-Y promoters, and 9 peach NF-Y genes were shown to distinctly increase their transcript abundances under drought stress.

Conclusions

This study identified 24 NF-Y genes in the peach genome and analysed their properties at different levels, providing a foundation for researchers to understand this gene family in peach. The up-regulation of 9 NF-Y genes under drought stress indicates that they can serve as candidate functional genes to further study drought resistance in peach.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5968-7) contains supplementary material, which is available to authorized users.

Three Main Genes in the MAPK Cascade Involved in the Chinese Jujube-Phytoplasma Interaction

Chinese jujube (Ziziphus jujuba Mill.) is an important economic forest species and multipurpose fruit tree in the family of Rhamnaceae. Phytoplasmas are significant prokaryotic pathogens, associated with more than 1000 plant diseases. Jujube witches’ broom disease (JWB) is a typical phytoplasma disease, caused by ‘Candidatus Phytoplasma ziziphi’. Mitogen-activated protein kinase (MAPK) cascades are highly universal signal transduction modules and play crucial roles in regulating innate immune responses in plants. Thus, in the current study, systematical expression profiles of 10 ZjMPK and 4 ZjMPKK genes were conducted in plantlets with JWB disease, plantlets recovered from JWB disease, the tissues showing different disease symptoms, and resistant/susceptible cultivars infected by JWB phytoplasma. We found that most ZjMPK and ZjMKK genes exhibited significant up- or down-regulation expression under phytoplasma infection, but the top three differentially expressed genes (DEGs) were ZjMPK2, ZjMKK2 and ZjMKK4, which showed the biggest times of gene’s significant difference expression in all materials. Based on STRING database analysis, ZjMKK2 and ZjMPK2 were involved in the same plant-pathogen interaction pathway, and Yeast two-hybrid screening showed that ZjMKK2 could interact with ZjMPK2. Finally, we deduced a pathway of jujube MAPK cascades which response to ‘Candidatus Phytoplasma ziziphi’ infection. Our study presents the first gene-family-wide investigation on the systematical expression analysis of MAPK and MAPKK genes in Chinese jujube under phytoplasma infection. These results provide valuable information for the further research on the signaling pathway of phytoplasma infection in Chinese jujube.

A B-box zinc finger protein, MdBBX10, enhanced salt and drought stresses tolerance in Arabidopsis

The expression of MdBBX10 was significantly induced by different stresses and ABA treatments. Overexpression of MdBBX10 in Arabidopsis significantly enhanced abiotic stresses tolerance by ABA signalling. The roles of B-box domain(s) containing proteins (BBXs) in regulation of flowering and light morphogenesis of plants were intensively studied. However, the roles of plant BBXs in abiotic stresses are poorly understood. A B-box protein encoding gene from apple (MdBBX10) was found to be up-regulated from gene expression profile under salt stress. qRT-PCR analysis indicated that the expression of MdBBX10 was significantly induced by different stresses and exogenous abscisic acid (ABA) in apple roots and leaves. The β-glucuronidase activity driven by the promoter of MdBBX10 was also strongly induced by NaCl, H₂O₂, polyethylene glycol and exogenous ABA, which was consistent to the existence of rich cis-acting elements related to the abiotic stresses in the promoter sequence. Over-expression of MdBBX10 in Arabidopsis significantly enhanced tolerance to abiotic stresses, with higher germination ratio and longer length of roots than the wild type plants. Transgenic plants of over-expressing MdBBX10 lines were more sensitive to exogenous ABA than the wild type plants. Under abiotic stress treatments, the transcript levels of ABA- and stress-related genes were higher in MdBBX10-overexpressing plants than wild type plants. Over-expression of MdBBX10 could enhance plant's ability to scavenge reactive oxygen species (ROS) under stresses, which is correlated with the expression of ROS-scavenging genes. These results provided the evidences that MdBBX10 plays an important role in enhanced plant tolerance to abiotic stresses, which were involved in ABA-mediated response and ROS response.

The cotton MAPK kinase GhMPK20 negatively regulates resistance to Fusarium oxysporum by mediating the MKK4-MPK20-WRKY40 cascade

Fusarium wilt is one of the most serious diseases affecting cotton. However, the pathogenesis and mechanism by which Fusarium oxysporum overcomes plant defence responses are unclear. Here, a new group D mitogen-activated protein kinase (MAPK) gene, GhMPK20, was identified and functionally analysed in cotton. GhMPK20 expression was significantly induced by F. oxysporum. Virus-induced gene silencing (VIGS) of GhMPK20 in cotton increased the tolerance to F. oxysporum, whereas ectopic GhMPK20 overexpression in Nicotiana benthamiana reduced F. oxysporum resistance via disruption of the salicylic acid (SA)-mediated defence pathway. More importantly, an F. oxysporum-induced MAPK cascade pathway composed of GhMKK4, GhMPK20 and GhWRKY40 was identified. VIGS of GhMKK4 and GhWRKY40 also enhanced F. oxysporum resistance in cotton, and the function of GhMKK4-GhMPK20 was shown to be essential for F. oxysporum-induced GhWRKY40 expression. Together, our results indicate that the GhMKK4-GhMPK20-GhWRKY40 cascade in cotton plays an important role in the pathogenesis of F. oxysporum. This research broadens our knowledge of the negative role of the MAPK cascade in disease resistance in cotton and provides an important scientific basis for the formulation of Fusarium wilt prevention strategies.

Genome-wide classification, evolutionary analysis and gene expression patterns of the kinome in Gossypium

The protein kinase (PK, kinome) family is one of the largest families in plants and regulates almost all aspects of plant processes, including plant development and stress responses. Despite their important functions, comprehensive functional classification, evolutionary analysis and expression patterns of the cotton PK gene family has yet to be performed on PK genes. In this study, we identified the cotton kinomes in the Gossypium raimondii, Gossypium arboretum, Gossypium hirsutum and Gossypium barbadense genomes and classified them into 7 groups and 122-24 subfamilies using software HMMER v3.0 scanning and neighbor-joining (NJ) phylogenetic analysis. Some conserved exon-intron structures were identified not only in cotton species but also in primitive plants, ferns and moss, suggesting the significant function and ancient origination of these PK genes. Collinearity analysis revealed that 16.6 million years ago (Mya) cotton-specific whole genome duplication (WGD) events may have played a partial role in the expansion of the cotton kinomes, whereas tandem duplication (TD) events mainly contributed to the expansion of the cotton RLK group. Synteny analysis revealed that tetraploidization of G. hirsutum and G. barbadense contributed to the expansion of G. hirsutum and G. barbadense PKs. Global expression analysis of cotton PKs revealed stress-specific and fiber development-related expression patterns, suggesting that many cotton PKs might be involved in the regulation of the stress response and fiber development processes. This study provides foundational information for further studies on the evolution and molecular function of cotton PKs.

Cell and Developmental Biology of Plant Mitogen-Activated Protein Kinases

Plant mitogen-activated protein kinases (MAPKs) constitute a network of signaling cascades responsible for transducing extracellular stimuli and decoding them to dedicated cellular and developmental responses that shape the plant body. Over the last decade, we have accumulated information about how MAPK modules control the development of reproductive tissues and gametes and the embryogenic and postembryonic development of vegetative organs such as roots, root nodules, shoots, and leaves. Of key importance to understanding how MAPKs participate in developmental and environmental signaling is the characterization of their subcellular localization, their interactions with upstream signal perception mechanisms, and the means by which they target their substrates. In this review, we summarize the roles of MAPK signaling in the regulation of key plant developmental processes, and we survey what is known about the mechanisms guiding the subcellular compartmentalization of MAPK modules.

Recent insights into cotton functional genomics: progress and future perspectives

Functional genomics has transformed from futuristic concept to well-established scientific discipline during the last decade. Cotton functional genomics promise to enhance the understanding of fundamental plant biology to systematically exploit genetic resources for the improvement of cotton fibre quality and yield, as well as utilization of genetic information for germplasm improvement. However, determining the cotton gene functions is a much more challenging task, which has not progressed at a rapid pace. This article presents a comprehensive overview of the recent tools and resources available with the major advances in cotton functional genomics to develop elite cotton genotypes. This effort ultimately helps to filter a subset of genes that can be used to assemble a final list of candidate genes that could be employed in future novel cotton breeding programme. We argue that next stage of cotton functional genomics requires the draft genomes refinement, re-sequencing broad diversity panels with the development of high-throughput functional genomics tools and integrating multidisciplinary approaches in upcoming cotton improvement programmes.

Nuclear Signaling of Plant MAPKs

Mitogen-activated protein kinases (MAPKs) are conserved protein kinases in eukaryotes that establish signaling modules where MAPK kinase kinases (MAPKKKs) activate MAPK kinases (MAPKKs) which in turn activate MAPKs. In plants, they are involved in the signaling of multiple environmental stresses and developmental programs. MAPKs phosphorylate their substrates and this post-translational modification (PTM) contributes to the regulation of proteins. PTMs may indeed modify the activity, subcellular localization, stability or trans-interactions of modified proteins. Plant MAPKs usually localize to the cytosol and/or nucleus, and in some instances they may also translocate from the cytosol to the nucleus. Upon the detection of environmental changes at the cell surface, MAPKs participate in the signal transduction to the nucleus, allowing an adequate transcriptional reprogramming. The identification of plant MAPK substrates largely contributed to a better understanding of the underlying signaling mechanisms. In this review, we highlight the nuclear signaling of plant MAPKs. We discuss the activation, regulation and activity of plant MAPKs, as well as their nuclear re-localization. We also describe and discuss known nuclear substrates of plant MAPKs in the context of biotic stress, abiotic stress and development and consider future research directions in the field of plant MAPKs.

GhMAP3K65, a Cotton Raf-Like MAP3K Gene, Enhances Susceptibility to Pathogen Infection and Heat Stress by Negatively Modulating Growth and Development in Transgenic Nicotiana benthamiana

Mitogen-activated protein kinase kinase kinases (MAP3Ks), the top components of MAPK cascades, modulate many biological processes, such as growth, development and various environmental stresses. Nevertheless, the roles of MAP3Ks remain poorly understood in cotton. In this study, GhMAP3K65 was identified in cotton, and its transcription was inducible by pathogen infection, heat stress, and multiple signalling molecules. Silencing of GhMAP3K65 enhanced resistance to pathogen infection and heat stress in cotton. In contrast, overexpression of GhMAP3K65 enhanced susceptibility to pathogen infection and heat stress in transgenic Nicotiana benthamiana. The expression of defence-associated genes was activated in transgenic N. benthamiana plants after pathogen infection and heat stress, indicating that GhMAP3K65 positively regulates plant defence responses. Nevertheless, transgenic N. benthamiana plants impaired lignin biosynthesis and stomatal immunity in their leaves and repressed vitality of their root systems. In addition, the expression of lignin biosynthesis genes and lignin content were inhibited after pathogen infection and heat stress. Collectively, these results demonstrate that GhMAP3K65 enhances susceptibility to pathogen infection and heat stress by negatively modulating growth and development in transgenic N. benthamiana plants.

Genome-wide identification and analysis of MAPK and MAPKK gene family in Chinese jujube (Ziziphus jujuba Mill.)

Background

Chinese jujube (Ziziphus jujuba Mill.) is one of the most important members in the Rhamnaceae family. The whole genome sequence and more than 30,000 proteins of Chinese jujube have been obtained in 2014. Mitogen-activated protein kinase cascades are universal signal transduction modules in plants, which is rapidly activated under various biotic and abiotic stresses. To date, there has been no comprehensive analysis of the MAPK and MAPKK gene family in Chinese jujube at the whole genome level.

Results

By performing a series of bioinformatics analysis, ten MAPK and five MAPKK genes were identified from the genome database of Chinese jujube, and then compared with the homologous genes from Arabidopsis. Phylogenetic analysis showed that ZjMAPKs was classified into four known groups, including A, B, C and D. ZjMAPKs contains five members of the TEY phosphorylation site and five members with the TDY motif. The ZjMAPKK family was subsequently divided into three groups, A, B and D. The gene structure, conserved motifs, functional annotation and chromosome distribution of ZjMAPKs and ZjMAPKKs were also predicted. ZjMAPKs and ZjMAPKKs were distributed on nine pseudo-chromosomes of Chinese jujube. Subsequently, expression analysis of ZjMAPK and ZjMAPKK genes using reverse transcription PCR and quantitative real-time PCR was carried out. The majority of ZjMAPK and ZjMAPKK genes were expressed in all tested organs/tissues with considerable differences in transcript levels indicating that they might be constitutively expressed. Moreover, ZjMKK5 was specific expressed in early development stage of jujube flower bud, indicating it plays some roles in reproductive organs development. The transcript expression of most ZjMAPK and ZjMAPKK genes was down-regulated in response to plant growth regulators, darkness treatment and phytoplasma infection.

Conclusions

We identified ten ZjMAPK and five ZjMAPKK genes from the genome database of Chinese jujube, the research results shown that ZjMPKs and ZjMKKs have the different expression patterns, indicating that they might play different roles in response to various treatments. The results provide valuable information for the further elucidation of physiological functions and biological roles of jujube MAPKs and MAPKKs.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4259-4) contains supplementary material, which is available to authorized users.

Genome-Wide Identification and Analysis of MAPK and MAPKK Gene Families in Bread Wheat (Triticum aestivum L.)

The mitogen-activated protein kinase (MAPK) cascade is a universal signal transduction module that plays a vital role in regulating growth and development, as well as environmental stress responses in plants. Wheat is one of the most important crops worldwide. Although the MAPK kinase kinase (MAP3K) family in wheat has been investigated, the MAPK and MAPK kinase (MAP2K) gene families remain unknown at present. Here, 54 MAPK and 18 MAPKK genes were identified in wheat using recent genomic information. Phylogenetic analysis of Triticum aestivum L. MAPKs and MAPKKs (TaMAPKs and TaMAPKKs) together with homologous genes from other species classified them into four groups, and the clustering was consistent with the genomic exon/intron structures. Conserved motif analysis found that MAPK proteins contained a typical TXY phosphorylation site and MAPKK proteins contained an S/T-X5-S/T motif. RNA-seq data mapping analysis showed that MAPK and MAPKK genes in group IV had tissue-specific expression profiles, whereas each group I member showed relatively high expression in all organs. Expression patterns of TaMAPK and TaMAPKK genes under stress conditions were also investigated and stress-responsive candidates were identified. Co-expression network analysis identified 11 TaMAPK genes and 6 TaMAPKK genes involved in the interaction network pathway. Overall, this study provided useful information for evolutionary and functional surveys of MAPK and MAPKK gene families in wheat and beyond.

Reduced Drought Tolerance by CRISPR/Cas9-Mediated SlMAPK3 Mutagenesis in Tomato Plants

Drought stress is one of the most destructive environmental factors that affect tomato plants adversely. Mitogen-activated protein kinases (MAPKs) are important signaling molecules that respond to drought stress. In this study, SlMAPK3 was induced by drought stress, and the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system was utilized to generate slmapk3 mutants. Two independent T1 transgenic lines and wild-type (WT) tomato plants were used for analysis of drought tolerance. Compared with WT plants, slmapk3 mutants exhibited more severe wilting symptom, higher hydrogen peroxide content, lower antioxidant enzymes activities, and suffered more membrane damage under drought stress. Furthermore, knockout of SlMAPK3 led to up- or down-regulated expressions of drought stress-responsive genes including SlLOX, SlGST, and SlDREB. The results suggest that SlMAPK3 is involved in drought response in tomato plants by protecting cell membranes from oxidative damage and modulating transcription of stress-related genes.

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.

Drought coping strategies in cotton: increased crop per drop

The growth and yield of many crops, including cotton, are affected by water deficit. Cotton has evolved drought specific as well as general morpho-physiological, biochemical and molecular responses to drought stress, which are discussed in this review. The key physiological responses against drought stress in cotton, including stomata closing, root development, cellular adaptations, photosynthesis, abscisic acid (ABA) and jasmonic acid (JA) production and reactive oxygen species (ROS) scavenging, have been identified by researchers. Drought stress induces the expression of stress-related transcription factors and genes, such as ROS scavenging, ABA or mitogen-activated protein kinases (MAPK) signalling genes, which activate various drought-related pathways to induce tolerance in the plant. It is crucial to elucidate and induce drought-tolerant traits via quantitative trait loci (QTL) analysis, transgenic approaches and exogenous application of substances. The current review article highlights the natural as well as engineered drought tolerance strategies in cotton.

A Raf-like MAPKKK gene, GhRaf19, negatively regulates tolerance to drought and salt and positively regulates resistance to cold stress by modulating reactive oxygen species in cotton

Mitogen-activated protein kinase kinase kinases (MAPKKKs) function at the top level of MAPK cascades and play important roles in plant development and stress responses. Although MAPKKKs comprise the largest family in the MAPK cascades, very few Raf-like MAPKKKs have been functionally identified, especially in the economically important crop cotton. In this study, a Raf-like MAPKKK gene, GhRaf19, was characterized for the first time in cotton. Our data show that the expression of GhRaf19 was inhibited by PEG and NaCl and induced by cold (4°C) and H₂O₂. Furthermore, when GhRaf19 was silenced in cotton using virus-induced gene silencing (VIGS), tolerance to drought and salt stress were enhanced, the accumulation of reactive oxygen species (ROS) was reduced, and ROS-related gene expression was increased. Consistent with these results, in N. benthamiana, overexpressing-GhRaf19 reduced tolerance to drought and salt. However, GhRaf19-silenced plants showed lowered resistance to cold in cotton, and this effect was correlated with the accumulation of ROS. In contrast, overexpressing GhRaf19 in N. benthamiana increased resistance to cold by inducing higher levels of expression and activity of ROS-related antioxidant genes/enzymes. These results indicate that GhRaf19 negatively regulates tolerance to drought and salt and positively regulates resistance to cold stress by modulating cellular ROS in cotton.

The Cotton WRKY Gene GhWRKY41 Positively Regulates Salt and Drought Stress Tolerance in Transgenic Nicotiana benthamiana

WRKY transcription factors constitute a very large family of proteins in plants and participate in modulating plant biological processes, such as growth, development and stress responses. However, the exact roles of WRKY proteins are unclear, particularly in non-model plants. In this study, Gossypium hirsutum WRKY41 (GhWRKY41) was isolated and transformed into Nicotiana benthamiana. Our results showed that overexpression of GhWRKY41 enhanced the drought and salt stress tolerance of transgenic Nicotiana benthamiana. The transgenic plants exhibited lower malondialdehyde content and higher antioxidant enzyme activity, and the expression of antioxidant genes was upregulated in transgenic plants exposed to osmotic stress. A β-glucuronidase (GUS) staining assay showed that GhWRKY41 was highly expressed in the stomata when plants were exposed to osmotic stress, and plants overexpressing GhWRKY41 exhibited enhanced stomatal closure when they were exposed to osmotic stress. Taken together, our findings demonstrate that GhWRKY41 may enhance plant tolerance to stress by functioning as a positive regulator of stoma closure and by regulating reactive oxygen species (ROS) scavenging and the expression of antioxidant genes.

A cotton Raf-like MAP3K gene, GhMAP3K40, mediates reduced tolerance to biotic and abiotic stress in Nicotiana benthamiana by negatively regulating growth and development

Mitogen-activated protein kinase (MAPK) cascades mediate various responses in plants. As the top component, MAP3Ks deserve more attention; however, little is known about the role of MAP3Ks, especially in cotton, a worldwide economic crop. In this study, a gene encoding a putative Raf-like MAP3K, GhMAP3K40, was isolated. GhMAP3K40 expression was induced by stress and multiple signal molecules. The plants overexpressing GhMAP3K40 had an enhanced tolerance to drought and salt stress at the germination stage. However, at the seedling stage, the transgenic plants suffered more severe damage after drought, exposure to pathogens and oxidative stress. The defence-related genes and the antioxidant system were activated in transgenic palnts, suggesting that GhMAP3K40 positively regulate the defence response. The transgenic plants were less able to prevent pathogenic invasion, which was due to defects in the cell structure of the leaves. The root system of the control plants were stronger compared with the transgenic plants. These results indicated a negative role of GhMAP3K40 in growth and development and GhMAP3K40 possibly caused the defects by down-regulating the lignin biosynthesis. Overall, these results suggest that GhMAP3K40 may positively regulate defence response but cause reduced tolerance to biotic and abiotic stress by negatively regulating growth and development.

Constitutive expression of DaCBF7, an Antarctic vascular plant Deschampsia antarctica CBF homolog, resulted in improved cold tolerance in transgenic rice plants

Deschampsia antarctica is an Antarctic hairgrass that grows on the west coast of the Antarctic peninsula. In this report, we have identified and characterized a transcription factor, D. antarctica C-repeat binding factor 7 (DaCBF7), that is a member of the monocot group V CBF homologs. The protein contains a single AP2 domain, a putative nuclear localization signal, and the typical CBF signature. DaCBF7, like other monocot group V homologs, contains a distinct polypeptide stretch composed of 43 amino acids in front of the AP2 motif. DaCBF7 was predominantly localized to nuclei and interacted with the C-repeat/dehydration responsive element (CRT/DRE) core sequence (ACCGAC) in vitro. DaCBF7 was induced by abiotic stresses, including drought, cold, and salinity. To investigate its possible cellular role in cold tolerance, a transgenic rice system was employed. DaCBF7-overexpressing transgenic rice plants (Ubi:DaCBF7) exhibited markedly increased tolerance to cold stress compared to wild-type plants without growth defects; however, overexpression of DaCBF7 exerted little effect on tolerance to drought or salt stress. Transcriptome analysis of a Ubi:DaCBF7 transgenic line revealed 13 genes that were up-regulated in DaCBF7-overexpressing plants compared to wild-type plants in the absence of cold stress and in short- or long-term cold stress. Five of these genes, dehydrin, remorin, Os03g63870, Os11g34790, and Os10g22630, contained putative CRT/DRE or low-temperature responsive elements in their promoter regions. These results suggest that overexpression of DaCBF7 directly and indirectly induces diverse genes in transgenic rice plants and confers enhanced tolerance to cold stress.

Analyzing serial cDNA libraries revealed reactive oxygen species and gibberellins signaling pathways in the salt response of Upland cotton (Gossypium hirsutum L.)

By comparing series full-length cDNA libraries stressed and control, the dynamic process of salt stress response in Upland cotton was studied, and reactive oxygen species and gibberellins signaling pathways were proposed. The Upland cotton is the most important fiber plant with highly salt tolerance. However, the molecular mechanism underlying salt tolerance in domesticated cotton was unclear. Here, seven full-length cDNA libraries were constructed for seedling roots of Upland cotton 'Zhong G 5' at 0, 3, 12 and 48 h after the treatment of control or 150 mM NaCl stress. About 3300 colonies in each library were selected robotically for 5'-end pyrosequencing, resulting in 20,358 expressed sequence tags (ESTs) totally. And 8516 uniESTs were then assembled, including 2914 contigs and 5602 singletons, and explored for Gene Ontology (GO) function. GO comparison between serial stress libraries and control reflected the growth regulation, stimulus response, signal transduction and biology regulation processes were conducted dynamically in response to salt stress. MYB, MYB-related, WRKY, bHLH, GRAS and ERF families of transcription factors were significantly enriched in the early response. 65 differentially expressed genes (DEGs), mainly associated with reactive oxygen species (ROS) scavenging, gibberellins (GAs) metabolism, signal transduction, transcription regulation, stress response and transmembrane transport, were identified and confirmed by quantitative real-time PCR. Overexpression of selected DEGs increased tolerance against salt stress in transgenic yeast. Results in this study supported that a ROS-GAs interacting signaling pathway of salt stress response was activated in Upland cotton. Our results provided valuable gene resources for further investigation of the molecular mechanism of salinity tolerance.

GhWRKY68 reduces resistance to salt and drought in transgenic Nicotiana benthamiana

The WRKY transcription factors modulate numerous physiological processes, including plant growth, development and responses to various environmental stresses. Currently, our understanding of the functions of the majority of the WRKY family members and their possible roles in signalling crosstalk is limited. In particular, very few WRKYs have been identified and characterised from an economically important crop, cotton. In this study, we characterised a novel group IIc WRKY gene, GhWRKY68, which is induced by different abiotic stresses and multiple defence-related signalling molecules. The β-glucuronidase activity driven by the GhWRKY68 promoter was enhanced after exposure to drought, salt, abscisic acid (ABA) and H2O2. The overexpression of GhWRKY68 in Nicotiana benthamiana reduced resistance to drought and salt and affected several physiological indices. GhWRKY68 may mediate salt and drought responses by modulating ABA content and enhancing the transcript levels of ABA-responsive genes. GhWRKY68-overexpressing plants exhibited reduced tolerance to oxidative stress after drought and salt stress treatments, which correlated with the accumulation of reactive oxygen species (ROS), reduced enzyme activities, elevated malondialdehyde (MDA) content and altered ROS-related gene expression. These results indicate that GhWRKY68 is a transcription factor that responds to drought and salt stresses by regulating ABA signalling and modulating cellular ROS.

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.

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.

MAPK cascades and major abiotic stresses

Plants have evolved with complex signaling circuits that operate under multiple conditions and govern numerous cellular functions. Stress signaling in plant cells is a sophisticated network composed of interacting proteins organized into tiered cascades where the function of a molecule is dependent on the interaction and the activation of another. In a linear scheme, the receptors of cell surface sense the stimuli and convey stress signals through specific pathways and downstream phosphorylation events controlled by mitogen-activated protein (MAP) kinases and second messengers, leading to appropriate adaptive responses. The specificity of the pathway is guided by scaffolding proteins and docking domains inside the interacting partners with distinctive structures and functions. The flexibility and the fine-tuned organization of the signaling molecules drive the activated MAP kinases into the appropriate location and connection to control and integrate the information flow. Here, we overview recent findings of the involvement of MAP kinases in major abiotic stresses (drought, cold and temperature fluctuations) and we shed light on the complexity and the specificity of MAP kinase signaling modules.