title: Genome-wide identification of MAPK, MAPKK, and MAPKKK gene families and transcriptional profiling analysis during development and stress response in cucumber.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. jieer881018@163.com.|Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Ministry of Agriculture, Hangzhou, 310058, China. jieer881018@163.com.
authors.forename: Jie
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. wpanchangtian@163.com.|Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Ministry of Agriculture, Hangzhou, 310058, China. wpanchangtian@163.com.
authors.forename: Changtian
authors.initials: C
authors.lastname: Pan
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. wangyan89416@163.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. 707137378@qq.com.
authors.forename: Lei
authors.initials: L
authors.lastname: Ye
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. Wujian1738555@163.com.
authors.forename: Jian
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. 704909820@qq.com.
authors.forename: Lifei
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. 1275051219@qq.com.|Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Ministry of Agriculture, Hangzhou, 310058, China. 1275051219@qq.com.
authors.forename: Tao
authors.initials: T
authors.lastname: Zou
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, 310058, China. glu@zju.edu.cn.|Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Ministry of Agriculture, Hangzhou, 310058, China. glu@zju.edu.cn.
authors.forename: Gang
authors.initials: G
authors.lastname: Lu
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002874:Chromosome Mapping; D017124:Conserved Sequence; D018553:Cucumis sativus / Q000166:cytology / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D019143:Evolution, Molecular; D020440:Gene Duplication; D020869:Gene Expression Profiling; D018745:Genome, Plant / Q000235:genetics; D023281:Genomics; D020930:MAP Kinase Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000235:genetics; D020929:Mitogen-Activated Protein Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013312:Stress, Physiological / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D010937:Plant Growth Regulators; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases