title: Analysis of two in planta expressed LysM effector homologs from the fungus Mycosphaerella graminicola reveals novel functional properties and varying contributions to virulence on wheat.
abstract: Secreted effector proteins enable plant pathogenic fungi to manipulate host defenses for successful infection. Mycosphaerella graminicola causes Septoria tritici blotch disease of wheat (Triticum aestivum) leaves. Leaf infection involves a long (approximately 7 d) period of symptomless intercellular colonization prior to the appearance of necrotic disease lesions. Therefore, M. graminicola is considered as a hemibiotrophic (or necrotrophic) pathogen. Here, we describe the molecular and functional characterization of M. graminicola homologs of Ecp6 (for extracellular protein 6), the Lysin (LysM) domain-containing effector from the biotrophic tomato (Solanum lycopersicum) leaf mold fungus Cladosporium fulvum, which interferes with chitin-triggered immunity in plants. Three LysM effector homologs are present in the M. graminicola genome, referred to as Mg3LysM, Mg1LysM, and MgxLysM. Mg3LysM and Mg1LysM genes were strongly transcriptionally up-regulated specifically during symptomless leaf infection. Both proteins bind chitin; however, only Mg3LysM blocked the elicitation of chitin-induced plant defenses. In contrast to C. fulvum Ecp6, both Mg1LysM and Mg3LysM also protected fungal hyphae against plant-derived hydrolytic enzymes, and both genes show significantly more nucleotide polymorphism giving rise to nonsynonymous amino acid changes. While Mg1LysM deletion mutant strains of M. graminicola were fully pathogenic toward wheat leaves, Mg3LysM mutant strains were severely impaired in leaf colonization, did not trigger lesion formation, and were unable to undergo asexual sporulation. This virulence defect correlated with more rapid and pronounced expression of wheat defense genes during the symptomless phase of leaf colonization. These data highlight different functions for MgLysM effector homologs during plant infection, including novel activities that distinguish these proteins from C. fulvum Ecp6.
authors.affiliation: Centre for Sustainable Pest and Disease Management, Department of Plant Pathology and Microbiology, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom.
authors.forename: Rosalind
authors.initials: R
authors.lastname: Marshall
authors.forename: Anja
authors.initials: A
authors.lastname: Kombrink
authors.forename: Juliet
authors.initials: J
authors.lastname: Motteram
authors.forename: Elisa
authors.initials: E
authors.lastname: Loza-Reyes
authors.forename: John
authors.initials: J
authors.lastname: Lucas
authors.forename: Kim E
authors.initials: KE
authors.lastname: Hammond-Kosack
authors.forename: Bart P H J
authors.initials: BP
authors.lastname: Thomma
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Rudd
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification / Q000472:pathogenicity*; D002686:Chitin / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D018506:Gene Expression Regulation, Plant; D005800:Genes, Fungal / Q000235:genetics; D006868:Hydrolysis; D025301:Hyphae / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D057865:Plant Immunity / Q000235:genetics; D018515:Plant Leaves / Q000382:microbiology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014908:Triticum / Q000201:enzymology / Q000235:genetics / Q000382:microbiology*; D015854:Up-Regulation / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D005656:Fungal Proteins; D002686:Chitin