title: Cell wall integrity and high osmolarity glycerol pathways are required for adaptation of Alternaria brassicicola to cell wall stress caused by brassicaceous indolic phytoalexins.
abstract: Camalexin, the characteristic phytoalexin of Arabidopsis thaliana, inhibits growth of the fungal necrotroph Alternaria brassicicola. This plant metabolite probably exerts its antifungal toxicity by causing cell membrane damage. Here we observed that activation of a cellular response to this damage requires cell wall integrity (CWI) and the high osmolarity glycerol (HOG) pathways. Camalexin was found to activate both AbHog1 and AbSlt2 MAP kinases, and activation of the latter was abrogated in a AbHog1 deficient strain. Mutant strains lacking functional MAP kinases showed hypersensitivity to camalexin and brassinin, a structurally related phytoalexin produced by several cultivated Brassica species. Enhanced susceptibility to the membrane permeabilization activity of camalexin was observed for MAP kinase deficient mutants. These results suggest that the two signalling pathways have a pivotal role in regulating a cellular compensatory response to preserve cell integrity during exposure to camalexin. AbHog1 and AbSlt2 deficient mutants had reduced virulence on host plants that may, at least for the latter mutants, partially result from their inability to cope with defence metabolites such as indolic phytoalexins. This constitutes the first evidence that a phytoalexin activates fungal MAP kinases and that outputs of activated cascades contribute to protecting the fungus against antimicrobial plant metabolites.
authors.affiliation: UMR PaVe no. 77, IFR 149 QUASAV, 2 Bd Lavoisier, F-49045 Angers Cedex, France.
authors.forename: Aymeric
authors.initials: A
authors.lastname: Joubert
authors.forename: Nelly
authors.initials: N
authors.lastname: Bataille-Simoneau
authors.forename: Claire
authors.initials: C
authors.lastname: Campion
authors.forename: Thomas
authors.initials: T
authors.lastname: Guillemette
authors.forename: Piétrick
authors.initials: P
authors.lastname: Hudhomme
authors.forename: Béatrice
authors.initials: B
authors.lastname: Iacomi-Vasilescu
authors.forename: Thibault
authors.initials: T
authors.lastname: Leroy
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Pochon
authors.forename: Pascal
authors.initials: P
authors.lastname: Poupard
authors.forename: Philippe
authors.initials: P
authors.lastname: Simoneau
mesh_terms: D000222:Adaptation, Physiological; D000528:Alternaria / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology*; D000935:Antifungal Agents / Q000633:toxicity*; D017360:Arabidopsis / Q000737:chemistry; D001937:Brassica / Q000737:chemistry; D002473:Cell Wall / Q000502:physiology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005990:Glycerol / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D009994:Osmolar Concentration; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D012717:Sesquiterpenes / Q000633:toxicity*; D013312:Stress, Physiological; D014774:Virulence; D000094162:Phytoalexins
chemical_list: D000935:Antifungal Agents; D005656:Fungal Proteins; D012717:Sesquiterpenes; D005990:Glycerol; D000094162:Phytoalexins