title: The mitogen-activated protein kinase BcSak1 of Botrytis cinerea is required for pathogenic development and has broad regulatory functions beyond stress response.
abstract: The mitogen-activated protein kinase (MAPK) BcSak1 of Botrytis cinerea is activated upon exposure to H(2)O(2) and, hence, might be involved in coping with oxidative stress during infection. However, beside osmotic and oxidative stress sensitivity, Δbcsak1 mutants have a pleiotropic phenotype, as they do not produce conidia and are unable to penetrate unwounded host tissue. In this study, the role of BcSak1 was investigated in the stress response and during infection of French beans by Botrytis cinerea. Using a macroarray approach, it was shown that BcSak1 is only marginally involved in the specific oxidative stress response. In fact, the induction of several genes after oxidative stress treatment is BcSak1-dependent, but most of these genes are also induced under conditions of osmotic stress. The majority of genes regulated by BcSak1 are not involved in the stress response at all. Using a translational fusion of BcSak1 to green fluorescent protein, it was shown clearly that the localization of this MAPK depends on the type of stress being applied; it associates rapidly to the nucleus only under osmotic stress. Therefore, a model is proposed in which BcSak1 acts in the cytosol by activation of one or more transcription factors under oxidative stress and, at the same time, it reacts to osmotic stress by migrating to the nucleus. Interestingly, the MAPK is also involved in the regulation of secondary metabolism, as the major phytotoxins secreted by this fungus are reduced in the Δbcsak1 deletion mutant. Experiments done in planta underlined the essential role of BcSak1 in the early stages of infection, when it translocates to the nucleus and then changes to cytosolic distribution during hyphal growth within the tissue.
authors.affiliation: Institut fuer Biologie und Biotechnologie def Pflanzen, Westf. Wilhelms-Universitaet, Muenster, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Heller
authors.forename: Nadja
authors.initials: N
authors.lastname: Ruhnke
authors.forename: José Juan
authors.initials: JJ
authors.lastname: Espino
authors.forename: Michelli
authors.initials: M
authors.lastname: Massaroli
authors.forename: Isidro Gonzalez
authors.initials: IG
authors.lastname: Collado
authors.forename: Paul
authors.initials: P
authors.lastname: Tudzynski
mesh_terms: D020171:Botrytis / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D027805:Phaseolus / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D002374:Catalase; D020928:Mitogen-Activated Protein Kinases