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

Surviving a Double-Edged Sword: Response of Horticultural Crops to Multiple Abiotic Stressors

Climate change-induced weather events, such as extreme temperatures, prolonged drought spells, or flooding, pose an enormous risk to crop productivity. Studies on the implications of multiple stresses may vary from those on a single stress. Usually, these stresses coincide, amplifying the extent of collateral damage and contributing to significant financial losses. The breadth of investigations focusing on the response of horticultural crops to a single abiotic stress is immense. However, the tolerance mechanisms of horticultural crops to multiple abiotic stresses remain poorly understood. In this review, we described the most prevalent types of abiotic stresses that occur simultaneously and discussed them in in-depth detail regarding the physiological and molecular responses of horticultural crops. In particular, we discussed the transcriptional, posttranscriptional, and metabolic responses of horticultural crops to multiple abiotic stresses. Strategies to breed multi-stress-resilient lines have been presented. Our manuscript presents an interesting amount of proposed knowledge that could be valuable in generating resilient genotypes for multiple stressors.

Emerging Roles of Mitogen-Activated Protein Kinase Signaling Pathways in the Regulation of Fruit Ripening and Postharvest Quality

Fleshy fruit ripening is a unique biological process that involves dramatic changes in a diverse array of cellular metabolisms. The regulation of these metabolisms is essentially mediated by cellular signal transduction of internal (e.g., hormones) and external cues (i.e., environmental stimuli). Mitogen-activated protein kinase (MAPK) signaling pathways play crucial roles in a diverse array of biological processes, such as plant growth, development and biotic/abiotic responses. Accumulating evidence suggests that MAPK signaling pathways are also implicated in fruit ripening and quality formation. However, while MAPK signaling has been extensively reviewed in Arabidopsis and some crop plants, the comprehensive picture of how MAPK signaling regulates fruit ripening and quality formation remains unclear. In this review, we summarize and discuss research in this area. We first summarize recent studies on the expression patterns of related kinase members in relation to fruit development and ripening and then summarize and discuss the crucial evidence of the involvement of MAPK signaling in fruit ripening and quality formation. Finally, we propose several perspectives, highlighting the research matters and questions that should be afforded particular attention in future studies.

Comprehensive genome-wide identification and functional characterization of MAPK cascade gene families in Nelumbo

Mitogen-activated protein kinase (MAPK) cascade signaling pathway plays pivotal roles in various plant biological processes. However, systematic study of MAPK cascade gene families is yet to be conducted in lotus. Herein, 198 putative MAPK genes, including 152 MAP3Ks, 15 MKKs, and 31 MPKs genes were identified in Nelumbo. Segmental duplication was identified as the predominant factor driving MAPK cascade gene family expansion in lotus. MAPK cascade genes in N. nucifera and N. lutea shared high degree of sequence homologies, with 84, 9, and 19 homologous MAP3K, MKK, and MPK gene pairs being detected between the two species, respectively, with most genes predominantly undergoing purifying selection. Gene expression profiling indicated that NnMAPK cascade genes were extensively involved in plant development and submergence stress response. Co-expression analysis revealed potential interaction between transcription factors (TFs) and NnMAPK cascade genes in various biological processes. NnMKK showed predicted interactions with multiple NnMAP3K or NnMPK proteins, which suggested that functional diversity of MAPK cascade genes could be as a result of their complex protein interaction mechanisms. This first systematic analysis of MAPK cascade families in lotus provides deeper insights into their evolutionary dynamics and functional properties, which potentially could be crucial for lotus genetic improvement.

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.

Comprehensive analysis of MAPK gene family in Populus trichocarpa and physiological characterization of PtMAPK3-1 in response to MeJA induction

Mitogen-activated protein kinases (MAPKs) play important roles in plant growth and development, as well as hormone and stress responses by signaling to eukaryotic cells, through MAPK cascade, the presence of various cues; thereby, regulating various responses. The MAPK cascade consists mainly of three gene families, MAPK, MAPKK, and MAPKKK, which activate downstream signaling pathways through sequential phosphorylation. Although the MAPK cascade gene family has been reported in several species, there is a lack of comprehensive analysis in poplar. We identified 21 MAPK genes, 11 MAPKK genes, and 104 MAPKKK genes in Populus trichocarpa. The phylogenetic classification was supported by conservative motif, gene structure and motif analysis. Whole genome duplication has an important role in the expansion of MAPK cascade genes. Analysis of promoter cis-elements and expression profiles indicates that MAPK cascade genes have important roles in plant growth and development, abiotic and biotic stresses, and phytohormone response. Expression profiling revealed a significant upregulation of PtMAPK3-1 expression in response to drought, salt and disease stresses. Poplar transiently overexpressing PtMAPK3-1 and treated with methyl jasmonic acid (MeJA) had higher catalase and peroxidase levels than non-overexpressing poplar. This work represents the first complete inventory of the MAPK cascade in P. trichocarpa, which reveals that PtMAPK3-1 is induced by the MeJA hormone and participates in the MeJA-induced enhancement of the antioxidant enzyme system.

Identification of Bottle Gourd (Lagenaria siceraria) OVATE Family Genes and Functional Characterization of LsOVATE1

The OVATE gene family is a class of conserved transcription factors that play significant roles in plant growth, development, and abiotic stress, and also affect fruit shape in vegetable crops. Bottle gourd (Lagenaria siceraria), commonly known as calabash or gourd, is an annual climber belonging to the Cucurbitaceae family. Studies on bottle gourd OVATE genes are limited. In this study, we performed genome-wide identification of the OVATE gene family in bottle gourd, and identified a total of 20 OVATE family genes. The identified genes were unevenly distributed across 11 bottle gourd chromosomes. We also analyzed the gene homology, amino acid sequence conservation, and three-dimensional protein structure (via prediction) of the 20 OVATE family genes. We used RNA-seq data to perform expression analysis, which found 20 OVATE family genes to be differentially expressed based on spatial and temporal characteristics, suggesting that they have varying functions in the growth and development of bottle gourd. In situ hybridization and subcellular localization analysis showed that the expression characteristics of the LsOVATE1 gene, located on chromosome 7 homologous to OVATE, is a candidate gene for affecting the fruit shape of bottle gourd. In addition, RT-qPCR data from bottle gourd roots, stems, leaves, and flowers showed different spatial expression of the LsOVATE1 gene. The ectopic expression of LsOVATE1 in tomato generated a phenotype with a distinct fruit shape and development. Transgenic-positive plants that overexpressed LsOVATE1 had cone-shaped fruit, calyx hypertrophy, petal degeneration, and petal retention after flowering. Our results indicate that LsOVATE1 could serve important roles in bottle gourd development and fruit shape determination, and provide a basis for future research into the function of LsOVATE1.

TaMPK2B, a member of the MAPK family in T. aestivum, enhances plant low-Pi stress tolerance through modulating physiological processes associated with phosphorus starvation defensiveness

The mitogen-activated protein kinase (MAPK) cascades are present in plant species and modulate plant growth and stress responses. This study characterizes TaMPK2B, a MAPK family gene in T. aestivum that regulates plant adaptation to low-Pi stress. TaMPK2B harbors the conserved domains involving protein phosphorylation and protein-protein interaction. A yeast two-hybrid assay reveals an interaction between TaMPK2B and TaMPKK2 and between the latter and TaMPKKK;A, suggesting that all comprise a MAPK signaling cascade TaMPKKK;A-TaMPKK2-TaMPK2B. TaMPK2B expression levels were elevated in roots and leaves under a Pi starvation (PS) condition. Additionally, the induced TaMPK2B transcripts under PS in tissues were gradually restored following the Pi normal recovery condition. TaMPK2B overexpression conferred on plants improved PS adaptation; the tobacco lines with TaMPK2B overexpression enhanced the plant's dry mass production, Pi uptake capacity, root system architecture (RSA) establishment, and ROS homeostasis relative to wild type under PS treatment. Moreover, the transcripts of genes in phosphate transporter (PT), PIN-FORMED, and antioxidant enzyme (AE) families, including NtPT3 and NtPT4, NtPIN9, and NtMnSOD1 and NtPOD1;7, were elevated in Pi-deprived lines overexpressing TaMPK2B. Transgene analyses validated their functions in regulating Pi uptake, RSA establishment, and AE activities of plants treated by PS. These results suggest that TaMPK2B-mediated plant PS adaptation is correlated with the modified transcription of distinct PT, PIN, and AE genes. Our investigation suggests that TaMPK2B is one of the crucial regulators in plant low-Pi adaptation by improving Pi uptake, RSA formation, and ROS homeostasis via transcriptionally regulating genes associated with the above physiological processes.

Genome-Wide Identification and Expression Analysis of MAPK Gene Family in Lettuce (Lactuca sativa L.) and Functional Analysis of LsMAPK4 in High- Temperature-Induced Bolting

The mitogen-activated protein kinase (MAPK) pathway is a widely distributed signaling cascade in eukaryotes and is involved in regulating plant growth, development, and stress responses. High temperature, a frequently occurring environmental stressor, causes premature bolting in lettuce with quality decline and yield loss. However, whether MAPKs play roles in thermally induced bolting remains poorly understood. In this study, 17 LsMAPK family members were identified from the lettuce genome. The physical and chemical properties, subcellular localization, chromosome localization, phylogeny, gene structure, family evolution, cis-acting elements, and phosphorylation sites of the LsMAPK gene family were evaluated via in silico analysis. According to phylogenetic relationships, LsMAPKs can be divided into four groups, A, B, C, and D, which is supported by analyses of gene structure and conserved domains. The collinearity analysis showed that there were 5 collinearity pairs among LsMAPKs, 8 with AtMAPKs, and 13 with SlMAPKs. The predicted cis-acting elements and potential phosphorylation sites were closely associated with hormones, stress resistance, growth, and development. Expression analysis showed that most LsMAPKs respond to high temperatures, among which LsMAPK4 is significantly and continuously upregulated upon heat treatments. Under heat stress, the stem length of the LsMAPK4-knockdown lines was significantly shorter than that of the control plants, and the microscope observations demonstrated that the differentiation time of flower buds at the stem apex was delayed accordingly. Therefore, silencing of LsMAPK4 significantly inhibited the high- temperature-accelerated bolting in lettuce, indicating that LsMPAK4 might be a potential regulator of lettuce bolting. This study provides a theoretical basis for a better understanding of the molecular mechanisms underlying the MAPK genes in high-temperature-induced bolting.

Functional analysis of mitogen-activated protein kinases (MAPKs) in potato under biotic and abiotic stress

Biotic and abiotic stresses are the main constrain of potato (Solanum tuberosum L.) production all over the world. To overcome these hurdles, many techniques and mechanisms have been used for increasing food demand for increasing population. One of such mechanism is mitogen-activated protein kinase (MAPK) cascade, which is significance regulators of MAPK pathway under various biotic and abiotic stress conditions in plants. However, the acute role in potato for various biotic and abiotic resistance is not fully understood. In eukaryotes including plants, MAPK transfer information from sensors to responses. In potato, biotic and abiotic stresses, as well as a range of developmental responses including differentiation, proliferation, and cell death in plants, MAPK plays an essential role in transduction of diverse extracellular stimuli. Different biotic and abiotic stress stimuli such as pathogen (bacteria, virus, and fungi, etc.) infections, drought, high and low temperatures, high salinity, and high or low osmolarity are induced by several MAPK cascade and MAPK gene families in potato crop. The MAPK cascade is synchronized by numerous mechanisms, including not only transcriptional regulation but also through posttranscriptional regulation such as protein-protein interactions. In this review, we will discuss the recent detailed functional analysis of certain specific MAPK gene families which are involved in resistance to various biotic and abiotic stresses in potato. This study will also provide new insights into functional analysis of various MAPK gene families in biotic and abiotic stress response as well as its possible mechanism.

In-silico genome wide analysis of Mitogen activated protein kinase kinase kinase gene family in C. sinensis

Mitogen activated protein kinase kinase kinase (MAPKKK) form the upstream component of MAPK cascade. It is well characterized in several plants such as Arabidopsis and rice however the knowledge about MAPKKKs in tea plant is largely unknown. In the present study, MAPKKK genes of tea were obtained through a genome wide search using Arabidopsis thaliana as the reference genome. Among 59 candidate MAPKKK genes in tea, 17 genes were MEKK-like, 31 genes were Raf-like and 11 genes were ZIK- like. Additionally, phylogenetic relationships were established along with structural analysis, which includes gene structure, its location as well as conserved motifs, cis-acting regulatory elements and functional domain signatures that were systematically examined. Also, on the basis of one orthologous gene found between tea and Arabidopsis, functional interaction was carried out in C. sinensis based on an Arabidopsis association model. The expressional profiles indicated major involvement of MAPKKK genes from tea in response to various abiotic stress factors. Taken together, this study provides the targets for additional inclusive identification, functional study, and provides comprehensive knowledge for a better understanding of the MAPKKK cascade regulatory network in C. sinensis.

Genome-wide analysis of mitogen-activated protein (MAP) kinase gene family expression in response to biotic and abiotic stresses in sugarcane

To systematically analyze mitogen-activated protein (MAP) kinase gene families and their expression profiles in sugarcane (Saccharum spp. hybrids; Sh) under diverse biotic and abiotic stresses, we identified 15 ShMAPKs, 6 ShMAPKKs and 16 ShMAPKKKs genes in the sugarcane cultivar R570 genome. These were also confirmed in one S. spontaneum genome and two transcriptome datasets of sugarcane trigged by Acidovorax avenae subsp. avenae (Aaa) and Xanthomonas albilineans (Xa) infections. Phylogenetic analysis revealed that four subgroups were present in each ShMAPK and ShMAPKK family and three sub-families (RAF, MEKK and ZIK) presented in the ShMAPKKK family. Conserved protein motif and gene structure analyses supported the evolutionary relationships of the three families inferred from the phylogenetic analysis. All of the ShMAPK, ShMAPKK and ShMAPKKK genes identified in Saccharum spp. R570 were distributed on chromosomes 1-7 and 9-10. RNA-seq and qRT-PCR analyses indicated that ShMAPK07 and ShMAPKKK02 were defense-responsive genes in sugarcane challenged by both Aaa and Xa stimuli, while some genes were upregulated specifically by Aaa and Xa infection. Additionally, ShMAPK05 acted as a negative regulator under drought and salinity stress, but served as a positive regulator under salicylic acid (SA) treatment. ShMAPK07 plays a positive role under drought stress, but a negative role under SA treatment. ShMAPKKK01 was negatively modulated by both salinity stress and SA treatment, whereas ShMAPKKK06 was positively regulated by both of the two stress stimuli. Our results suggest that members of MAPK cascade gene families regulate adverse stress responses through multiple signal transduction pathways in sugarcane.

Genome-wide identification and characterization of SRO gene family in wheat: Molecular evolution and expression profiles during different stresses

SRO (SIMILAR TO RCD ONE), a type of plant-specific small protein family, play important roles in plant growth and development, as well as in response to biotic/abiotic stresses. Although characterization of SROs have been performed in model plants, little is known about their function in wheat, especially under stress conditions. In this study, 30 SRO genes were identified from the wheat genome (TaSRO). They were phylogenetically separated into two groups with distinct structures. The cis-regulatory elements in the promoter region of TaSROs were analyzed and numerous elements functionally associated with stress responding and hormones were interpreted, implying the reason for induction expression patterns of TaSROs during abiotic and biotic stresses in wheat. Whole-genome replication events in the SRO gene family of wheat and seven other species (Arabidopsis thaliana, rice, maize, barley, soybean, upland cotton, and cucumber) were analyzed, resulting in 1, 12, 9, 23, 6, 5, and 3 of gene pairs, respectively. The tissue-specific expression pattern profiling revealed that most TaSROs are highly expressed in one or more tissues and may play an important role in wheat growth and development. In addition, qRT-PCR results further confirmed that these TaSRO genes are involved in wheat stress response. In summary, our study laid a theoretical basis for molecular function deciphering of TaSROs, especially in plant hormones and biotic/abiotic stress responses.

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.

Cloning, molecular and functional characterization by overexpression in Arabidopsis of MAPKK genes from grapevine (Vitis vinifera)

BACKGROUND

The mitogen-activated protein kinases (MAPKs), as a part of the MAPKKK-MAPKK-MAPK cascade, play crucial roles in plant development as an intracellular signal transduction pathway to respond various environmental signals. However, few MAPKK have been functionally characterized in grapevine.

RESULTS

In the study, five MAPKK (MKK) members were identified in grapevine (cultivar 'Pinot Noir'), cloned and designated as VvMKK1-VvMKK5. A phylogenetic analysis grouped them into four sub-families based on the similarity of their conserved motifs and gene structure to Arabidopsis MAPKK members. qRT-PCR results indicated that the expression of VvMKK1, VvMKK2, VvMKK4, and VvMKK5 were up-regulated in mature leaf and young blades, and roots, but exhibited low expression in leaf petioles. VvMKK2, VvMKK3, and VvMKK5 genes were differentially up-regulated when grapevine leaves were inoculated with spores of Erisyphe necator, or treated with salicylic acid (SA), ethylene (ETH), H2O2, or exposed to drought, indicating that these genes may be involved in a variety of signaling pathways. Over expression of VvMKK2 and VvMKK4 genes in transgenic Arabidopsis plants resulted in the production of seeds with a significantly higher germination and survival rate, and better seedling growth under stress conditions than wild-type plants. Overexpression of VvMKK2 in Arabidopsis improved salt and drought stress tolerance while overexpression of VvMKK4 only improved salt stress tolerance.

CONCLUSIONS

Results of the present investigation provide a better understanding of the interaction and function of MAPKKK-MAPKK-MAPK genes at the transcriptional level in grapevine and led to the identification of candidate genes for drought and salt stress in grapes.

Genome-wide identification of MAPKKK genes and their responses to phytoplasma infection in Chinese jujube (Ziziphus jujuba Mill.)

BACKGROUND

Mitogen-activated protein kinase (MAPK) cascades play vital roles in signal transduction in response to a wide range of biotic and abiotic stresses. In a previous study, we identified ten ZjMAPKs and five ZjMAPKKs in the Chinese jujube genome. We found that some members of ZjMAPKs and ZjMAPKKs may play key roles in the plant's response to phytoplasma infection. However, how these ZjMAPKKs are modulated by ZjMAPKKKs during the response process has not been elucidated. Little information is available regarding MAPKKKs in Chinese jujube.

RESULTS

A total of 56 ZjMAPKKKs were identified in the jujube genome. All of these kinases contain the key S-TKc (serine/threonine protein kinase) domain, which is distributed among all 12 chromosomes. Phylogenetic analyses show that these ZjMAPKKKs can be classified into two subfamilies. Specifically, 41 ZjMAPKKKs belong to the Raf subfamily, and 15 belong to the MEKK subfamily. In addition, the ZjMAPKKKs in each subfamily share the same conserved motifs and gene structures. Only one pair of ZjMAPKKKs (15/16, on chromosome 5) was found to be tandemly duplicated. Using qPCR, the expression profiles of these MAPKKKs were investigated in response to infection with phytoplasma. In the three main infected tissues (witches' broom leaves, phyllody leaves, and apparently normal leaves), ZjMAPKKK26 and - 45 were significantly upregulated, and ZjMAPKKK3, - 43 and - 50 were significantly downregulated. ZjMAPKKK4, - 10, - 25 and - 44 were significantly and highly induced in sterile cultivated tissues infected by phytoplasma, while ZjMAPKKK6, - 7, - 17, - 18, - 30, - 34, - 35, - 37, - 40, - 41, - 43, - 46, - 52 and - 53 were significantly downregulated.

CONCLUSIONS

For the first time, we present an identification and classification analysis of ZjMAPKKKs. Some ZjMAPKKK genes may play key roles in the response to phytoplasma infection. This study provides an initial understanding of the mechanisms through which ZjMAPKKKs are involved in the response of Chinese jujube to phytoplasma infection.

Genome-wide characterization and expression profiling of the MAPKKK genes in Gossypium arboreum L

Mitogen-activated protein kinase kinase kinases (MAPKKKs) are important components of MAPK cascades, which have different functions during developmental processes and stress responses. To date, there has been no systematic investigation of this gene family in the diploid cotton Gossypium arboreum L. In this study, a genome-wide survey was performed that identified 78 MAPKKK genes in G. arboreum. Phylogenetic analysis classified these genes into three subgroups: 14 belonged to ZIK, 20 to MEKK, and 44 to Raf. Chromosome location, phylogeny, and the conserved protein motifs of the MAPKKK gene family in G. arboreum were analyzed. The MAPKKK genes had a scattered genomic distribution across 13 chromosomes. The members in the same subfamily shared similar conserved motifs. The MAPKKK expression patterns were analyzed in mature leaves, stems, roots, and at different ovule developmental stages, as well as under salt and drought stresses. Transcriptome analysis showed that 76 MAPKKK genes had different transcript accumulation patterns in the tested tissues and 38 MAPKKK genes were differentially expressed in response to salt and drought stresses. These results lay the foundation for understanding the complex mechanisms behind MAPKKK-mediated developmental processes and abiotic stress-signaling transduction pathways in cotton.

Isolation and expression analysis of Salt Overly Sensitive gene family in grapevine (Vitisvinifera) in response to salt and PEG stress

Salt stress is one of the major environmental constraints for the production and yield of grape (Vitis vinifera) worldwide. The SOS3 gene family is part of the Salt Overly Sensitive (SOS) signaling pathway, a well-defined signaling pathway known to play a role in plant response to salt stress. In this study, the grapevine SOS3 gene family was annotated and the role of the annotated genes in salinity stress response was characterized. Nine grapevine SOS3 genes was identified in the grapevine genome and was subsequently analyzed. The expression patterns of the nine VviSOS3 genes, as determined by reverse transcription quantitative PCR (RT-qPCR), varied greatly in leaves, roots, and stems of in-vitro grown Pinot noir grapevine cultivar(PN40024) in response to salt (250mM NaCl) and polyethylene glycol 6000 (PEG, osmolality equal to the salt treatment) treatments over a 36h time period. All of the VviSOS3 genes, except VviSOS3.7, were up-regulated in leaves in response to the salt and PEG treatments. The majority of VviSOS3 genes, except VviSOS3.8 were up-regulated in roots in response to the PEG stress, with an opposite expression pattern in the root and stem in response to salt stress. The salinity treatment decreased the soluble protein content. Based on the expression pattern and physiological data, VviSOS3.7 and VviSOS3.8 were identified as candidate genes for further functional characterizations regarding their role in the response of grapevine to salt stress.

Multispecies genome-wide analysis defines the MAP3K gene family in Gossypium hirsutum and reveals conserved family expansions

Background

Gene families are sets of structurally and evolutionarily related genes – in one or multiple species – that typically share a conserved biological function. As such, the identification and subsequent analyses of entire gene families are widely employed in the fields of evolutionary and functional genomics of both well established and newly sequenced plant genomes. Currently, plant gene families are typically identified using one of two major ways: 1) HMM-profile based searches using models built on Arabidopsis thaliana genes or 2) coding sequence homology searches using curated databases. Integrated databases containing functionally annotated genes and gene families have been developed for model organisms and several important crops; however, a comprehensive methodology for gene family annotation is currently lacking, preventing automated annotation of newly sequenced genomes.

Results

This paper proposes a combined measure of homology identification, motif conservation, phylogenomic and integrated gene expression analyses to define gene family structures in multiple plant species. The MAP3K gene families in seven plant species, including two currently unexamined species Gossypium hirsutum, and Zostera marina, were characterized to reveal new insights into their collective function and evolution and demonstrate the effectiveness of our novel methodology.

Conclusion

Compared with recent reports, this methodology performs significantly better for the identification and analysis of gene family members in several monocots/dicots, diploid as well as polyploid plant species.

Electronic supplementary material

The online version of this article (10.1186/s12859-019-2624-9) contains supplementary material, which is available to authorized users.

Genome-wide Identification of Jatropha curcas MAPK, MAPKK, and MAPKKK Gene Families and Their Expression Profile Under Cold Stress

Mitogen-activated protein kinase (MAPK) cascades are fundamental signal transduction modules in all eukaryotic organisms, controlling cell division, growth, development, and hormone signaling. Additionally, they can be activated in response to a variety of biotic and abiotic stressors. Although the evolution and expression patterns of MAPK cascade families have been systematically investigated in several model plants (e.g., Arabidopsis, rice, and poplar), we still know very little about MAPK, MAPKK, and MAPKKK families in Jatropha curcas, an economically important species. Therefore, this study performed genome-wide identification and transcriptional expression analysis of these three families in J. curcas. We identified 12 J. curcas MAPK (JcMAPKs), 5 JcMAPKKs, and 65 JcMAPKKKs. Phylogenetic analysis classified all JcMAPKs and JcMAPKKs into four subgroups, whereas JcMAPKKKs were grouped into three subfamilies (MEKK, RAF, and ZIK). Similarities in exon/intron structures supported the evolutionary relationships within subgroups and subfamilies. Conserved motif analysis indicated that all J. curcas MAPK cascades possessed typical, 200–300 amino-acid protein kinase domains. MAPK cascade genes were presented throughout all 11 chromosomes. Gene duplication analysis suggested that after JcMAPK and JcMAPKKK diverged, 3 and 19 tandem duplicates occurred under strong purifying selection. Furthermore, RNA-seq and qRT-PCR analyses revealed that some MAPK cascade genes are predominantly expressed in specific tissues. Moreover, their expression levels significantly increased under cold treatment. Our results should provide insight into the roles of MAPK cascade genes in regulating J. curcas stress responses and in hormonal signal transduction. Furthermore, these data have important applications in the genetic improvement of J. curcas.

Genome-Wide Bioinformatics Analysis of MAPK Gene Family in Kiwifruit (Actinidia Chinensis)

Mitogen activated protein kinase (MAPK) cascades are universal signal transduction modules that play crucial roles in various biotic and abiotic stresses, hormones, cell division, and developmental processes in plants. Mitogen activated protein kinase (MAPK/MPK), being a part of this cascade, performs an important function for further appropriate cellular responses. Although MAPKs have been investigated in several model plants, no systematic analysis has been conducted in kiwifruit (Actinidia chinensis). In the present study, we identified 18 putative MAPKs in the kiwifruit genome. This gene family was analyzed bioinformatically in terms of their chromosome locations, sequence alignment, gene structures, and phylogenetic and conserved motifs. All members possess fully canonical motif structures of MAPK. Phylogenetic analysis indicated that AcMAPKs could be classified into five subfamilies, and these gene motifs in the same group showed high similarity. Gene structure analysis demonstrated that the number of exons in AcMAPK genes ranged from 2 to 29, suggesting large variation among kiwifruit MAPK genes. The expression profiles of these AcMAPK genes were further investigated using quantitative real-time polymerase chain reaction (qRT-PCR), which demonstrated that AcMAPKs were induced or repressed by various biotic and abiotic stresses and hormone treatments, suggesting their potential roles in the biotic and abiotic stress response and various hormone signal transduction pathways in kiwifruit. The results of this study provide valuable insight into the putative physiological and biochemical functions of MAPK genes in kiwifruit.

Identification on mitogen-activated protein kinase signaling cascades by integrating protein interaction with transcriptional profiling analysis in cotton

Plant mitogen-activated protein kinase (MAPK) cascades play important roles in development and stress responses. In previous studies, we have systematically investigated the mitogen-activated protein kinase kinase (MKK) and MAPK gene families in cotton. However, the complete interactions between MAPK gene family members in MAPK signaling cascade is poorly characterized. Herein, we investigated the mitogen-activated protein kinase kinase kinase (MAPKKK) family members and identified a total of 89 MAPKKK genes in the Gossypium raimondii genome. We cloned 51 MAPKKKs in G. hirsutum and investigated the interactions between MKK and MAPKKK proteins through yeast-two hybrid assays. A total of 18 interactive protein pairs involved in 14 MAPKKKs and six MKKs were found. Among these, 13 interactive pairs had not been reported previously. Gene expression patterns revealed that 12 MAPKKKs were involved in diverse signaling pathways triggered by hormone treatments or abiotic stresses. By combining the MKK-MAPK and MKK-MAPKKK protein interactions with gene expression patterns, 38 potential MAPK signaling modules involved in the complicated cross-talks were identified, which provide a basis on elucidating biological function of the MAPK cascade in response to hormonal and/or stress responses. The systematic investigation in MAPK signaling cascades will lay a foundation for understanding the functional roles of different MAPK cascades in signal transduction pathways, and for the improvement of various defense responses in cotton.

Molecular Characterization and Co-expression Analysis of the SnRK2 Gene Family in Sugarcane (Saccharum officinarum L.)

In plants, both abscisic acid (ABA) dependent and independent pathways form the basis for the response to environmental stresses. Sucrose non-fermenting 1-related protein kinase 2 (SnRK2) plays a central role in plant stress signal transduction. However, complete annotation and specific expression patterns of SnRK2s in sugarcane remain unclear. For the present study, we performed a full-length cDNA library survey of sugarcane, thus identifying ten SoSnRK2 genes via phylogenetic, local BLAST methods, and various bioinformatics analyses. Phylogenetic analysis indicated division of SoSnRK2 genes into three subgroups, similar to other plant species. Gene structure comparison with Arabidopsis suggested a unique evolutionary imprint of the SnRK2 gene family in sugarcane. Both sequence alignment and structural annotation provided an overview of the conserved N-terminal and variations of the C-terminal, suggesting functional divergence. Transcript and transient expression assays revealed SoSnRK2s to be involved in the responses to diverse stress signals, and strong ABA induction of SoSnRK2s in subgroup III. Co-expression network analyses indicated the existence of both conserved and variable biological functions among different SoSnRK2s members. In summary, this comprehensive analysis will facilitate further studies of the SoSnRK2 family and provide useful information for the functional validation of SoSnRK2s.

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.

The MAPKKK gene family in cassava: Genome-wide identification and expression analysis against drought stress

Mitogen-activated protein kinase kinase kinases (MAPKKKs), an important unit of MAPK cascade, play crucial roles in plant development and response to various stresses. However, little is known concerning the MAPKKK family in the important subtropical and tropical crop cassava. In this study, 62 MAPKKK genes were identified in the cassava genome, and were classified into 3 subfamilies based on phylogenetic analysis. Most of MAPKKKs in the same subfamily shared similar gene structures and conserved motifs. The comprehensive transcriptome analysis showed that MAPKKK genes participated in tissue development and response to drought stress. Comparative expression profiles revealed that many MAPKKK genes were activated in cultivated varieties SC124 and Arg7 and the function of MeMAPKKKs in drought resistance may be different between SC124/Arg7 and W14. Expression analyses of the 7 selected MeMAPKKK genes showed that most of them were significantly upregulated by osmotic, salt and ABA treatments, whereas slightly induced by H₂O₂ and cold stresses. Taken together, this study identified candidate MeMAPKKK genes for genetic improvement of abiotic stress resistance and provided new insights into MAPKKK -mediated cassava resistance to drought stress.

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.

Genomewide analysis of the lateral organ boundaries domain gene family in Vitis vinifera

In plants, the transcription factor families have been implicated in many important biological processes. These processes include morphogenesis, signal transduction and environmental stress responses. Proteins containing the lateral organ boundaries domain (LBD), which encodes a zinc finger-like domain are only found in plants. This finding indicates that this unique gene family regulates only plant-specific biological processes. LBD genes play crucial roles in the growth and development of plants such as Arabidopsis, Oryza sativa, Zea mays, poplar, apple and tomato. However, relatively little is known about the LBD genes in grape (Vitis vinifera). In this study, we identified 40 LBD genes in the grape genome. A complete overview of the chromosomal locations, phylogenetic relationships, structures and expression profiles of this gene family during development in grape is presented here. Phylogenetic analysis showed that the LBD genes could be divided into classes I and II, together with LBDs from Arabidopsis. We mapped the 40 LBD genes on the grape chromosomes (chr1-chr19) and found that 37 of the predicted grape LBD genes were distributed in different densities across 12 chromosomes. Grape LBDs were found to share a similar intron/exon structure and gene length within the same class. The expression profiles of grape LBD genes at different developmental stages were analysed using microarray data. Results showed that 21 grape LBD genes may be involved in grape developmental processes, including preveraison, veraison and ripening. Finally, we analysed the expression patterns of six LBD genes through quantitative real-time polymerase chain reation analysis. The six LBD genes showed differential expression patterns among the three representative grape tissues, and five of these genes were found to be involved in responses to mannitol, sodium chloride, heat stress and low temperature treatments. To our knowledge, this is the first study to analyse the LBD gene family in grape and provides valuable information for classification and functional investigation of this gene family.

VqMAPKKK38 is essential for stilbene accumulation in grapevine

Vitis species, including grapevine, produce a class of secondary metabolites called stilbenes that are important for plant disease resistance and can have positive effects on human health. Mitogen-activated protein kinase (MAPK) signaling cascades not only play key roles in plant defense responses but also contribute to stilbene biosynthesis in grapevine. MAPKKKs function at the upper level of the MAPK network and initiate signaling through this pathway. In this study, a Raf-like MAPKKK gene, VqMAPKKK38, was identified and functionally characterized from the Chinese wild grapevine V. quinquangularis accession 'Danfeng-2'. We observed that VqMAPKKK38 transcript levels were elevated by powdery mildew infection, high salinity conditions and chilling stresses, as well as in response to treatments by the hormones salicylic acid (SA), methyl jasmonate (MeJA), ethylene (Eth) and abscisic acid (ABA). In addition, based on both transient overexpression and gene suppression of VqMAPKKK38 in grapevine leaves, we found that VqMAPKKK38 positively regulates stilbene synthase transcription and stilbene accumulation probably by mediating the activation of the transcription factor MYB14. In addition, both hydrogen peroxide (H₂O₂) and calcium influx activated VqMAPKKK38 expression and stilbene biosynthesis, which suggests that VqMAPKKK38 may be involved in the calcium signaling and ROS signaling pathways.

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.

Genome-wide characterisation and expression profile of the grapevine ATL ubiquitin ligase family reveal biotic and abiotic stress-responsive and development-related members

The Arabidopsis Tóxicos en Levadura (ATL) protein family is a class of E3 ubiquitin ligases with a characteristic RING-H2 Zn-finger structure that mediates diverse physiological processes and stress responses in plants. We carried out a genome-wide survey of grapevine (Vitis vinifera L.) ATL genes and retrieved 96 sequences containing the canonical ATL RING-H2 domain. We analysed their genomic organisation, gene structure and evolution, protein domains and phylogenetic relationships. Clustering revealed several clades, as already reported in Arabidopsis thaliana and rice (Oryza sativa), with an expanded subgroup of grapevine-specific genes. Most of the grapevine ATL genes lacked introns and were scattered among the 19 chromosomes, with a high level of duplication retention. Expression profiling revealed that some ATL genes are expressed specifically during early or late development and may participate in the juvenile to mature plant transition, whereas others may play a role in pathogen and/or abiotic stress responses, making them key candidates for further functional analysis. Our data offer the first genome-wide overview and annotation of the grapevine ATL family, and provide a basis for investigating the roles of specific family members in grapevine physiology and stress responses, as well as potential biotechnological applications.

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.

Phosphoproteomic analysis of induced resistance reveals activation of signal transduction processes by beneficial and pathogenic interaction in grapevine

Protein phosphorylation regulates several key processes of the plant immune system. Protein kinases and phosphatases are pivotal regulators of defense mechanisms elicited by resistance inducers. However, the phosphorylation cascades that trigger the induced resistance mechanisms in plants have not yet been deeply investigated. The beneficial fungus Trichoderma harzianum T39 (T39) induces resistance against grapevine downy mildew (Plasmopara viticola), but its efficacy could be further improved by a better understanding of the cellular regulations involved. We investigated quantitative changes in the grapevine phosphoproteome during T39-induced resistance to get an overview of regulatory mechanisms of downy mildew resistance. Immunodetection experiments revealed activation of the 45 and 49kDa kinases by T39 treatment both before and after pathogen inoculation, and the phosphoproteomic analysis identified 103 phosphopeptides that were significantly affected by the phosphorylation cascades during T39-induced resistance. Peptides affected by T39 treatment showed comparable phosphorylation levels after P. viticola inoculation, indicating activation of the microbial recognition machinery before pathogen infection. Phosphorylation profiles of proteins related to photosynthetic processes and protein ubiquitination indicated a partial overlap of cellular responses in T39-treated and control plants. However, phosphorylation changes of proteins involved in response to stimuli, signal transduction, hormone signaling, gene expression regulation, and RNA metabolism were exclusively elicited by P. viticola inoculation in T39-treated plants. These results highlighted the relevance of phosphorylation changes during T39-induced resistance and identified key regulator candidates of the grapevine defense against downy mildew.

Bioinformatics Analysis of MAPKKK Family Genes in Medicago truncatula

Mitogen-activated protein kinase kinase kinase (MAPKKK) is a component of the MAPK cascade pathway that plays an important role in plant growth, development, and response to abiotic stress, the functions of which have been well characterized in several plant species, such as Arabidopsis, rice, and maize. In this study, we performed genome-wide and systemic bioinformatics analysis of MAPKKK family genes in Medicago truncatula. In total, there were 73 MAPKKK family members identified by search of homologs, and they were classified into three subfamilies, MEKK, ZIK, and RAF. Based on the genomic duplication function, 72 MtMAPKKK genes were located throughout all chromosomes, but they cluster in different chromosomes. Using microarray data and high-throughput sequencing-data, we assessed their expression profiles in growth and development processes; these results provided evidence for exploring their important functions in developmental regulation, especially in the nodulation process. Furthermore, we investigated their expression in abiotic stresses by RNA-seq, which confirmed their critical roles in signal transduction and regulation processes under stress. In summary, our genome-wide, systemic characterization and expressional analysis of MtMAPKKK genes will provide insights that will be useful for characterizing the molecular functions of these genes in M. truncatula.

Emerging tools, concepts and ideas to track the modulator genes underlying plant drought adaptive traits: An overview

Crop vulnerability to multiple abiotic stresses is increasing at an alarming rate in the current global climate change scenario, especially drought. Crop improvement for adaptive adjustments to accomplish stress tolerance requires a comprehensive understanding of the key contributory processes. This requires the identification and careful analysis of the critical morpho-physiological plant attributes and their genetic control. In this review we try to discuss the crucial traits underlying drought tolerance and the various modes followed to understand their molecular level regulation. Plant stress biology is progressing into new dimensions and a conscious attempt has been made to traverse through the various approaches and checkpoints that would be relevant to tackle drought stress limitations for sustainable crop production.

Genome-Wide Identification and Expression Analysis of the WRKY Gene Family in Cassava

The WRKY family, a large family of transcription factors (TFs) found in higher plants, plays central roles in many aspects of physiological processes and adaption to environment. However, little information is available regarding the WRKY family in cassava (Manihot esculenta). In the present study, 85 WRKY genes were identified from the cassava genome and classified into three groups according to conserved WRKY domains and zinc-finger structure. Conserved motif analysis showed that all of the identified MeWRKYs had the conserved WRKY domain. Gene structure analysis suggested that the number of introns in MeWRKY genes varied from 1 to 5, with the majority of MeWRKY genes containing three exons. Expression profiles of MeWRKY genes in different tissues and in response to drought stress were analyzed using the RNA-seq technique. The results showed that 72 MeWRKY genes had differential expression in their transcript abundance and 78 MeWRKY genes were differentially expressed in response to drought stresses in different accessions, indicating their contribution to plant developmental processes and drought stress resistance in cassava. Finally, the expression of 9 WRKY genes was analyzed by qRT-PCR under osmotic, salt, ABA, H2O2, and cold treatments, indicating that MeWRKYs may be involved in different signaling pathways. Taken together, this systematic analysis identifies some tissue-specific and abiotic stress-responsive candidate MeWRKY genes for further functional assays in planta, and provides a solid foundation for understanding of abiotic stress responses and signal transduction mediated by WRKYs in cassava.

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.

Genome-Wide Identification and Expression Analysis of the NAC Transcription Factor Family in Cassava

NAC [no apical meristem (NAM), Arabidopsis transcription activation factor [ATAF1/2] and cup-shaped cotyledon (CUC2)] proteins is one of the largest groups of plant specific transcription factors and plays a crucial role in plant growth, development, and adaption to the environment. Currently, no information is known about the NAC family in cassava. In this study, 96 NAC genes (MeNACs) were identified from the cassava genome. Phylogenetic analysis of the NACs from cassava and Arabidopsis showed that MeNAC proteins can be clustered into 16 subgroups. Gene structure analysis found that the number of introns of MeNAC genes varied from 0 to 5, with the majority of MeNAC genes containing two introns, indicating a small gene structure diversity of cassava NAC genes. Conserved motif analysis revealed that all of the identified MeNACs had the conserved NAC domain and/or NAM domain. Global expression analysis suggested that MeNAC genes exhibited different expression profiles in different tissues between wild subspecies and cultivated varieties, indicating their involvement in the functional diversity of different accessions. Transcriptome analysis demonstrated that MeNACs had a widely transcriptional response to drought stress and that they had differential expression profiles in different accessions, implying their contribution to drought stress resistance in cassava. Finally, the expression of twelve MeNAC genes was analyzed under osmotic, salt, cold, ABA, and H₂O₂ treatments, indicating that cassava NACs may represent convergence points of different signaling pathways. Taken together, this work found some excellent tissue-specific and abiotic stress-responsive candidate MeNAC genes, which would provide a solid foundation for functional investigation of the NAC family, crop improvement and improved understanding of signal transduction in plants. These data bring new insight on the complexity of the transcriptional control of MeNAC genes and support the hypothesis that NACs play an important role in plant growth, development, and adaption of environment.

Genome-Wide Identification and Expression Analyses of Aquaporin Gene Family during Development and Abiotic Stress in Banana

Aquaporins (AQPs) function to selectively control the flow of water and other small molecules through biological membranes, playing crucial roles in various biological processes. However, little information is available on the AQP gene family in bananas. In this study, we identified 47 banana AQP genes based on the banana genome sequence. Evolutionary analysis of AQPs from banana, Arabidopsis, poplar, and rice indicated that banana AQPs (MaAQPs) were clustered into four subfamilies. Conserved motif analysis showed that all banana AQPs contained the typical AQP-like or major intrinsic protein (MIP) domain. Gene structure analysis suggested the majority of MaAQPs had two to four introns with a highly specific number and length for each subfamily. Expression analysis of MaAQP genes during fruit development and postharvest ripening showed that some MaAQP genes exhibited high expression levels during these stages, indicating the involvement of MaAQP genes in banana fruit development and ripening. Additionally, some MaAQP genes showed strong induction after stress treatment and therefore, may represent potential candidates for improving banana resistance to abiotic stress. Taken together, this study identified some excellent tissue-specific, fruit development- and ripening-dependent, and abiotic stress-responsive candidate MaAQP genes, which could lay a solid foundation for genetic improvement of banana cultivars.

Genome-wide identification of MAPK, MAPKK, and MAPKKK gene families and transcriptional profiling analysis during development and stress response in cucumber

Background

The mitogen-activated protein kinase (MAPK) cascade consists of three types of reversibly phosphorylated kinases, namely, MAPK, MAPK kinase (MAPKK/MEK), and MAPK kinase kinase (MAPKKK/MEKK), playing important roles in plant growth, development, and defense response. The MAPK cascade genes have been investigated in detail in model plants, including Arabidopsis, rice, and tomato, but poorly characterized in cucumber (Cucumis sativus L.), a major popular vegetable in Cucurbitaceae crops, which is highly susceptible to environmental stress and pathogen attack.

Results

A genome-wide analysis revealed the presence of at least 14 MAPKs, 6 MAPKKs, and 59 MAPKKKs in the cucumber genome. Phylogenetic analyses classified all the CsMAPK and CsMAPKK genes into four groups, whereas the CsMAPKKK genes were grouped into the MEKK, RAF, and ZIK subfamilies. The expansion of these three gene families was mainly contributed by segmental duplication events. Furthermore, the ratios of non-synonymous substitution rates (Ka) and synonymous substitution rates (Ks) implied that the duplicated gene pairs had experienced strong purifying selection. Real-time PCR analysis demonstrated that some MAPK, MAPKK and MAPKKK genes are preferentially expressed in specific organs or tissues. Moreover, the expression levels of most of these genes significantly changed under heat, cold, drought, and Pseudoperonospora cubensis treatments. Exposure to abscisic acid and jasmonic acid markedly affected the expression levels of these genes, thereby implying that they may play important roles in the plant hormone network.

Conclusion

A comprehensive genome-wide analysis of gene structure, chromosomal distribution, and evolutionary relationship of MAPK cascade genes in cucumber are present here. Further expression analysis revealed that these genes were involved in important signaling pathways for biotic and abiotic stress responses in cucumber, as well as the response to plant hormones. Our first systematic description of the MAPK, MAPKK, and MAPKKK families in cucumber will help to elucidate their biological roles in plant.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1621-2) contains supplementary material, which is available to authorized users.

Genome-wide identification and transcriptional expression analysis of mitogen-activated protein kinase and mitogen-activated protein kinase kinase genes in Capsicum annuum

The tripartite mitogen-activated protein kinase (MAPK) signaling cascades have been implicated in plant growth, development, and environment adaptation, but a comprehensive understanding of MAPK signaling at genome-wide level is limited in Capsicum annuum. Herein, genome-wide identification and transcriptional expression analysis of MAPK and MAPK kinase (MAPKK) were performed in pepper. A total of 19 pepper MAPK (CaMAPKs) genes and five MAPKK (CaMAPKKs) genes were identified. Phylogenetic analysis indicated that CaMAPKs and CaMAPKKs could be classified into four groups and each group contains similar exon-intron structures. However, significant divergences were also found. Notably, five members of the pepper MAPKK family were much less conserved than those found in Arabidopsis, and 9 Arabidopsis MAPKs did not have orthologs in pepper. Additionally, 7 MAPKs in Arabidopsis had either two or three orthologs in the pepper genome, and six pepper MAPKs and one MAPKK differing in sequence were found in three pepper varieties. Quantitative real-time RT-PCR analysis showed that the majority of MAPK and MAPKK genes were ubiquitously expressed and transcriptionally modified in pepper leaves after treatments with heat, salt, and Ralstonia solanacearum inoculation as well as exogenously applied salicylic acid, methyl jasmonate, ethephon, and abscisic acid. The MAPKK-MAPK interactome was tested by yeast two-hybrid assay, the results showed that one MAPKK might interact with multiple MAPKs, one MAPK might also interact with more than one MAPKKs, constituting MAPK signaling networks which may collaborate in transmitting upstream signals into appropriate downstream cellular responses and processes. These results will facilitate future functional characterization of MAPK cascades in 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.