Invasion of insect cells by Spiroplasma citri involves spiralin relocalization and lectin/glycoconjugate-type interactions.
Spiroplamas are helical, cell wall-less bacteria belonging to the Class Mollicutes, a group of microorganisms phylogenetically related to low G+C, Gram-positive bacteria. Spiroplasma species are all found associated with arthropods and a few, including Spiroplasma citri are pathogenic to plant. Thus S. citri has the ability to colonize cells of two very distinct hosts, the plant and the insect vector. While spiroplasmal factors involved in transmission by the leafhopper Circulifer haematoceps have been identified, their specific contribution to invasion of insect cells is poorly understood. In this study we provide evidence that the lipoprotein spiralin plays a major role in the very early step of cell invasion. Confocal laser scanning immunomicroscopy revealed a relocalization of spiralin at the contact zone of adhering spiroplasmas. The implication of a role for spiralin in adhesion to insect cells was further supported by adhesion assays showing that a spiralin-less mutant was impaired in adhesion and that recombinant spiralin triggered adhesion of latex beads. We also showed that cytochalasin D induced changes in the surface-exposed glycoconjugates, as inferred from the lectin binding patterns, and specifically improved adhesion of S. citri wild-type but not of the spiralin-less mutant. These results indicate that cytochalasin D exposes insect cell receptors of spiralin that are masked in untreated cells. In addition, competitive adhesion assays with lectins strongly suggest spiralin to exhibit glycoconjugate binding properties similar to that of the Vicia villosa agglutinin (VVA) lectin.
INRA, UMR 1332 Biologie du Fruit et Pathologie, Villenave d'Ornon, France; Université de Bordeaux, UMR 1332 Biologie du Fruit et Pathologie, Villenave d'Ornon, France.
Sybille
S
Duret
Brigitte
B
Batailler
Marie-Pierre
MP
Dubrana
Colette
C
Saillard
Joël
J
Renaudin
Laure
L
Béven
Nathalie
N
Arricau-Bouvery
D000818:Animals; D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000502:physiology*; D002460:Cell Line; D015638:Cytochalasin D / Q000494:pharmacology; D006430:Hemiptera / Q000166:cytology / Q000382:microbiology*; D054884:Host-Pathogen Interactions; D007303:Insect Vectors / Q000166:cytology / Q000382:microbiology*; D037102:Lectins / Q000378:metabolism; D008074:Lipoproteins / Q000502:physiology*; D010935:Plant Diseases / Q000382:microbiology; D021381:Protein Transport; D012469:Salivary Glands / Q000166:cytology / Q000378:metabolism; D045642:Spiroplasma citri / Q000502:physiology*; D050257:Tubulin Modulators / Q000494:pharmacology
D001425:Bacterial Outer Membrane Proteins; D037102:Lectins; D008074:Lipoproteins; D050257:Tubulin Modulators; C028588:spiralin; D015638:Cytochalasin D