title: The major antigenic membrane protein of "Candidatus Phytoplasma asteris" selectively interacts with ATP synthase and actin of leafhopper vectors.
abstract: Phytoplasmas, uncultivable phloem-limited phytopathogenic wall-less bacteria, represent a major threat to agriculture worldwide. They are transmitted in a persistent, propagative manner by phloem-sucking Hemipteran insects. Phytoplasma membrane proteins are in direct contact with hosts and are presumably involved in determining vector specificity. Such a role has been proposed for phytoplasma transmembrane proteins encoded by circular extrachromosomal elements, at least one of which is a plasmid. Little is known about the interactions between major phytoplasma antigenic membrane protein (Amp) and insect vector proteins. The aims of our work were to identify vector proteins interacting with Amp and to investigate their role in transmission specificity. In controlled transmission experiments, four Hemipteran species were identified as vectors of "Candidatus Phytoplasma asteris", the chrysanthemum yellows phytoplasmas (CYP) strain, and three others as non-vectors. Interactions between a labelled (recombinant) CYP Amp and insect proteins were analysed by far Western blots and affinity chromatography. Amp interacted specifically with a few proteins from vector species only. Among Amp-binding vector proteins, actin and both the α and β subunits of ATP synthase were identified by mass spectrometry and Western blots. Immunofluorescence confocal microscopy and Western blots of plasma membrane and mitochondrial fractions confirmed the localisation of ATP synthase, generally known as a mitochondrial protein, in plasma membranes of midgut and salivary gland cells in the vector Euscelidius variegatus. The vector-specific interaction between phytoplasma Amp and insect ATP synthase is demonstrated for the first time, and this work also supports the hypothesis that host actin is involved in the internalization and intracellular motility of phytoplasmas within their vectors. Phytoplasma Amp is hypothesized to play a crucial role in insect transmission specificity.
authors.affiliation: Istituto di Virologia Vegetale, Consiglio Nazionale delle Ricerche, Torino, Italy.
authors.forename: Luciana
authors.initials: L
authors.lastname: Galetto
authors.forename: Domenico
authors.initials: D
authors.lastname: Bosco
authors.forename: Raffaella
authors.initials: R
authors.lastname: Balestrini
authors.forename: Andrea
authors.initials: A
authors.lastname: Genre
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Fletcher
authors.forename: Cristina
authors.initials: C
authors.lastname: Marzachì
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000378:metabolism*; D015153:Blotting, Western; D006430:Hemiptera / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism; D007303:Insect Vectors / Q000166:cytology / Q000378:metabolism*; D042541:Intracellular Space / Q000378:metabolism; D008403:Mass Screening; D008565:Membrane Proteins / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D045582:Phytoplasma / Q000276:immunology; D011485:Protein Binding; D021381:Protein Transport; D013379:Substrate Specificity
chemical_list: D000199:Actins; D000942:Antigens, Bacterial; D019476:Insect Proteins; D008565:Membrane Proteins; D024101:Mitochondrial Proteins