title: Characterization, expression patterns and functional analysis of the MAPK and MAPKK genes in watermelon (Citrullus lanatus).
abstract: BACKGROUND
  Mitogen-activated protein kinase (MAPK) cascades, which consist of three functionally associated protein kinases, namely MEKKs, MKKs and MPKs, are universal signaling modules in all eukaryotes and have been shown to play critical roles in many physiological and biochemical processes in plants. However, little or nothing is known about the MPK and MKK families in watermelon.
  
  
  RESULTS
  In the present study, we performed a systematic characterization of the ClMPK and ClMKK families including the identification and nomenclature, chromosomal localization, phylogenetic relationships, ClMPK-ClMKK interactions, expression patterns in different tissues and in response to abiotic and biotic stress and transient expression-based functional analysis for their roles in disease resistance. Genome-wide survey identified fifteen ClMPK and six ClMKK genes in watermelon genome and phylogenetic analysis revealed that both of the ClMPK and ClMKK families can be classified into four distinct groups. Yeast two-hybrid assays demonstrated significant interactions between members of the ClMPK and ClMKK families, defining putative ClMKK2-1/ClMKK6-ClMPK4-1/ClMPK4-2/ClMPK13 and ClMKK5-ClMPK6 cascades. Most of the members in the ClMPK and ClMKK families showed differential expression patterns in different tissues and in response to abiotic (e.g. drought, salt, cold and heat treatments) and biotic (e.g. infection of Fusarium oxysporum f. sp. niveum) stresses. Transient expression of ClMPK1, ClMPK4-2 and ClMPK7 in Nicotiana benthamiana resulted in enhanced resistance to Botrytis cinerea and upregulated expression of defense genes while transient expression of ClMPK6 and ClMKK2-2 led to increased susceptibility to B. cinerea. Furthermore, transient expression of ClMPK7 also led to hypersensitive response (HR)-like cell death and significant accumulation of H2O2 in N. benthamiana.
  
  
  CONCLUSIONS
  We identified fifteen ClMPK and six ClMKK genes from watermelon and analyzed their phylogenetic relationships, expression patterns and protein-protein interactions and functions in disease resistance. Our results demonstrate that ClMPK1, ClMPK4-2 and ClMPK7 positively but ClMPK6 and ClMKK2-2 negatively regulate the resistance to B. cinerea when transiently expressed in N. benthamiana and that ClMPK7 functions as a regulator of HR-like cell death through modulating the generation of H2O2.
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Qiuming
authors.initials: Q
authors.lastname: Song
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Dayong
authors.initials: D
authors.lastname: Li
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Dai
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Shixia
authors.initials: S
authors.lastname: Liu
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Yongbo
authors.initials: Y
authors.lastname: Hong
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China. zhanghj82@zju.edu.cn.|College of Life Science, Taizhou University, Taizhou, Zhejiang, 318001, P. R. China. zhanghj82@zju.edu.cn.
authors.forename: Huijuan
authors.initials: H
authors.lastname: Zhang
authors.affiliation: State Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, P. R. China.
authors.forename: Fengming
authors.initials: F
authors.lastname: Song
mesh_terms: D000595:Amino Acid Sequence; D029773:Citrullus / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000382:microbiology; D060467:Disease Resistance; D018506:Gene Expression Regulation, Plant; D020929:Mitogen-Activated Protein Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D020928:Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D016415:Sequence Alignment
chemical_list: D010940:Plant Proteins; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases