Spiroplasma Transmission from Insects to Plants: S. citri Proteins Involved in Transmission by Leafhopper Vectors
Laure Béven, Saskia Hogenhout, Fabien Labroussaa, Nathalie Arricau-Bouvery and Colette Saillard
from: Mollicutes: Molecular Biology and Pathogenesis (Edited by: Glenn F. Browning and Christine Citti). Caister Academic Press, U.K. (2014)
Members of the genus Spiroplasma are motile, helical, wall-free eubacteria that are associated primarily with insects. Three spiroplasma species associated with plant disease are phloem restricted and transmitted in a persistent manner by sap-feeding leafhopper vectors. The spiroplasmas are acquired by the leafhoppers, traverse various insect tissues and then are transmitted to plants after having reached the leafhopper salivary glands. Thus, the spiroplasmas have to successfully passage different physical barriers of the gut and salivary glands. This involves specific protein-protein interactions between the spiroplasmas and insect tissues. Indeed, transmission electron microscopy studies indicated that spiroplasma invasion of gut epithelial cells occurs primarily by endocytosis at the brush border membranes and that upon invasion oval or flask-shaped spiroplasmas are inside membrane-bound vesicles. Confocal microscopy analyses of Spiroplasma citri-infected C. haematoceps salivary glands and cultured cell line (Ciha-1) experimentally infected by S. citri provided evidence that spiroplasmas associate with cell actin microfilaments. Adhesin-like proteins namely SARP1, ScARPs and SkARP are encoded on spiroplasma plasmids pBJS-O, pSci1-6 and pSKU146. Several other proteins including spiralin, ABC transporter solute binding protein and a phosphoglycerate kinase required for efficient transmission of S. citri by leafhoppers have been identified. The involvement of all these proteins in an interaction between the spiroplasma and the leafhopper cells is discussed in this chapter read more ...