title: Tomato SlMKK2 and SlMKK4 contribute to disease resistance against Botrytis cinerea.
abstract: BACKGROUND
  Mitogen-activated protein kinase (MAPK) cascades are highly conserved signaling modules that mediate the transduction of extracellular stimuli via receptors/sensors into intracellular responses and play key roles in plant immunity against pathogen attack. However, the function of tomato MAPK kinases, SlMKKs, in resistance against Botrytis cinerea remains unclear yet.
  
  
  RESULTS
  A total of five SlMKK genes with one new member, SlMKK5, were identified in tomato. qRT-PCR analyses revealed that expression of SlMKK2 and SlMKK4 was strongly induced by B. cinerea and by jasmonic acid and ethylene precursor 1-amino cyclopropane-1-carboxylic acid. Virus-induced gene silencing (VIGS)-based knockdown of individual SlMKKs and disease assays identified that SlMKK2 and SlMKK4 but not other three SlMKKs (SlMKK1, SlMKK3 and SlMKK5) are involved in resistance against B. cinerea. Silencing of SlMKK2 or SlMKK4 resulted in reduced resistance to B. cinerea, increased accumulation of reactive oxygen species and attenuated expression of defense genes after infection of B. cinerea in tomato plants. Furthermore, transient expression of constitutively active phosphomimicking forms SlMKK2DD and SlMKK4DD in leaves of Nicotiana benthamiana plants led to enhanced resistance to B. cinerea and elevated expression of defense genes.
  
  
  CONCLUSIONS
  VIGS-based knockdown of SlMKK2 and SlMKK4 expression in tomato and gain-of-function transient expression of constitutively active phosphomimicking forms SlMKK2DD and SlMKK2DD in N. benthamiana demonstrate that both SlMKK2 and SlMKK4 function as positive regulators of defense response against B. cinerea.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Li
authors.forename: Yafen
authors.initials: Y
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Ouyang
authors.forename: Yongbo
authors.initials: Y
authors.lastname: Hong
authors.forename: Huijuan
authors.initials: H
authors.lastname: Zhang
authors.forename: Dayong
authors.initials: D
authors.lastname: Li
authors.affiliation: National Key Laboratory for Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, Zhejiang 310058, China. fmsong@zju.edu.cn.
authors.forename: Fengming
authors.initials: F
authors.lastname: Song
mesh_terms: D020171:Botrytis / Q000187:drug effects / Q000502:physiology*; D060467:Disease Resistance / Q000187:drug effects / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D018551:Solanum lycopersicum / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000382:microbiology*; D010641:Phenotype; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics / Q000382:microbiology
chemical_list: D010937:Plant Growth Regulators; D010940:Plant Proteins; D017382:Reactive Oxygen Species