title: Combined microscopy and molecular analyses show phloem occlusions and cell wall modifications in tomato leaves in response to 'Candidatus Phytoplasma solani'.
abstract: Callose deposition, phloem-protein conformational changes and cell wall thickening are calcium-mediated occlusions occurring in the plant sieve elements in response to different biotic and abiotic stresses. However, the significance of these structures in plant-phytoplasma interactions requires in-depth investigations. We adopted a novel integrated approach, based on the combined use of microscopic and molecular analyses, to investigate the structural modifications induced in tomato leaf tissues in presence of phytoplasmas, focusing on vascular bundles and on the occlusion structures. Phloem hyperplasia and string-like arrangement of xylem vessels were found in infected vascular tissue. The diverse occlusion structures were differentially modulated in the phloem in response to phytoplasma infection. Callose amount was higher in midribs from infected plants than in healthy ones. Callose was observed at sieve plates but not at pore-plasmodesma units. A putative callose synthase gene encoding a protein with high similarity to Arabidopsis CalS7, responsible for callose deposition at sieve plates, was upregulated in symptomatic leaves, indicating a modulation in the response to stolbur infection. P-proteins showed configuration changes in infected sieve elements, exhibiting condensation of the filaments. The transcripts for a putative P-protein 2 and a sieve element occlusion-related protein were localized in the phloem but only the first one was modulated in the infected tissues.
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Udine, Udine, Italy.|INRA, Institut Jean-Pierre Bourgin, Versailles, France.
authors.forename: F
authors.initials: F
authors.lastname: De Marco
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Udine, Udine, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Pagliari
authors.affiliation: Department of Life Sciences, University of Parma, Parma, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Degola
authors.affiliation: Department of Phytopathology and Applied Zoology, Justus Liebig University, Giessen, Germany.
authors.forename: S V
authors.initials: SV
authors.lastname: Buxa
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Udine, Udine, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Loschi
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, Versailles, France.
authors.forename: S
authors.initials: S
authors.lastname: Dinant
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, Versailles, France.
authors.forename: R
authors.initials: R
authors.lastname: Le Hir
authors.affiliation: INRA, Institut Jean-Pierre Bourgin, Versailles, France.
authors.forename: H
authors.initials: H
authors.lastname: Morin
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Udine, Udine, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Santi
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Udine, Udine, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Musetti
mesh_terms: D002473:Cell Wall / Q000378:metabolism* / Q000382:microbiology*; D005936:Glucans / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D018551:Solanum lycopersicum / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism / Q000382:microbiology*; D008853:Microscopy / Q000379:methods*; D052585:Phloem / Q000166:cytology / Q000378:metabolism* / Q000382:microbiology*; D045582:Phytoplasma / Q000472:pathogenicity / Q000502:physiology*; D018515:Plant Leaves / Q000166:cytology / Q000201:enzymology / Q000378:metabolism / Q000382:microbiology
chemical_list: D005936:Glucans; C048306:callose; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase
keywords: Callose; P-proteins; phloem; phytoplasma; tomato