title: Expression and β-glucan binding properties of Scots pine (Pinus sylvestris L.) antimicrobial protein (Sp-AMP).
abstract: Scots pine (Pinus sylvestris) secretes a number of small, highly-related, disulfide-rich proteins (Sp-AMPs) in response to challenges with fungal pathogens such as Heterobasidion annosum, although their biological role has been unknown. Here, we examined the expression patterns of these genes, as well as the structure and function of the encoded proteins. Northern blots and quantitative real time PCR showed increased levels of expression that are sustained during the interactions of host trees with pathogens, but not non-pathogens, consistent with a function in conifer tree defenses. Furthermore, the genes were up-regulated after treatment with salicylic acid and an ethylene precursor, 1-aminocyclopropane-1-carboxylic-acid, but neither methyl jasmonate nor H(2)O(2) induced expression, indicating that Sp-AMP gene expression is independent of the jasmonic acid signaling pathways. The cDNA encoding one of the proteins was cloned and expressed in Pichia pastoris. The purified protein had antifungal activity against H. annosum, and caused morphological changes in its hyphae and spores. It was directly shown to bind soluble and insoluble β-(1,3)-glucans, specifically and with high affinity. Furthermore, addition of exogenous glucan is linked to higher levels of Sp-AMP expression in the conifer. Homology modeling and sequence comparisons suggest that a conserved patch on the surface of the globular Sp-AMP is a carbohydrate-binding site that can accommodate approximately four sugar units. We conclude that these proteins belong to a new family of antimicrobial proteins (PR-19) that are likely to act by binding the glucans that are a major component of fungal cell walls.
authors.affiliation: Department of Molecular Biology, Swedish University of Agricultural Sciences, Box 590, Biomedical Center, 75124 Uppsala, Sweden.
authors.forename: Sanjeewani
authors.initials: S
authors.lastname: Sooriyaarachchi
authors.forename: Emad
authors.initials: E
authors.lastname: Jaber
authors.forename: Adrian Suárez
authors.initials: AS
authors.lastname: Covarrubias
authors.forename: Wimal
authors.initials: W
authors.lastname: Ubhayasekera
authors.forename: Frederick O
authors.initials: FO
authors.lastname: Asiegbu
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Mowbray
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000595:Amino Acid Sequence; D000598:Amino Acids, Cyclic / Q000494:pharmacology; D001487:Basidiomycota / Q000378:metabolism / Q000502:physiology; D002473:Cell Wall / Q000378:metabolism; D003001:Cloning, Molecular; D003517:Cyclopentanes / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007113:Immunity, Innate; D054883:Oxylipins / Q000494:pharmacology; D010843:Pichia / Q000235:genetics; D041605:Pinus sylvestris / Q000378:metabolism* / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D020156:Salicylic Acid / Q000494:pharmacology; D016415:Sequence Alignment; D015398:Signal Transduction; D047071:beta-Glucans / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000085:Acetates; D000598:Amino Acids, Cyclic; D003517:Cyclopentanes; D054883:Oxylipins; D010940:Plant Proteins; D047071:beta-Glucans; C023863:1-aminocyclopropane-1-carboxylic acid; C072239:methyl jasmonate; D006861:Hydrogen Peroxide; D020156:Salicylic Acid