Evidence suggesting interactions between immunodominant membrane protein Imp of Flavescence dorée phytoplasma and protein extracts from distantly related insect species.

V Trivellone,E Angelini,M Ripamonti,L Filippin,M Rossi,L Galetto,C Marzachí

doi:10.1111/jam.14445

Abstract

In this study, binding between the immunodominant membrane protein Imp of the 16SrV-D phytoplasma associated with Flavescence dorée disease (FD-Dp) and insect proteins of vectors and non-vectors of FD-Dp was tested. Six Auchenorrhyncha species, from distantly related groups were selected: Scaphoideus titanus, Euscelidius variegatus, Macrosteles quadripunctulatus, Zyginidia pullula (Cicadomorpha), Ricania speculum and Metcalfa pruinosa (Fulgoromorpha). The vector status of each species was retrieved from the literature or determined by transmission trials in this study. A His-tagged partial Imp protein and a rabbit polyclonal antibody were synthesized and used for Western and Far-Western dot Blot (FWdB) experiments. Total native and membrane proteins (MP) were extracted from entire bodies and organs (gut and salivary glands) of each insect species. FWdB showed decreasing interaction intensities of Imp fusion protein with total proteins from entire bodies of S. titanus, E. variegatus (competent vectors) and M. quadripunctulatus (non-vector), while no interaction signal was detected with the other three species (non-vectors). A strong signal detected upon interaction of FD-D Imp and MP from guts of closely related insects supports the role of this organ as the first barrier to ensure successful transmission. Our results showed that specific Imp binding, correlated with vector status, is involved in interactions between FD-Dp and insect proteins. Integrating knowledge on host-pathogen protein-protein interactions and on insect phylogeny would help to identify the actual range of vectors of phytoplasma strains of economic importance.

Highlights

Phytoplasmas are phloem-limited wall-less plant pathogenic bacteria in the class Mollicutes causing hundreds of plant diseases worldwide and responsible for severe economic losses to agriculturally important plants (Strauss 2009; Marcone 2014)
We investigated the transmission specificity mediated by the immunodominant membrane protein Imp in the pathosystem of 16SrV-Dp and its insect hosts
Acquisition and inoculation experiments were performed in this study to assess the vector status of two species, M. quadripunctulatus and M. pruinosa, for which no detailed data on Acquisition Rate (AR) and Transmission Rate (TR) were available in the literature

Summary

Introduction

Phytoplasmas are phloem-limited wall-less plant pathogenic bacteria in the class Mollicutes causing hundreds of plant diseases worldwide and responsible for severe economic losses to agriculturally important plants (Strauss 2009; Marcone 2014). Phytoplasmas represent a well-defined monophyletic clade in the family Acholeplasmataceae, they are still treated as indefinite taxa due to severe difficulties hampering in vitro cultivation. The 16SrV phytoplasma (16SrVp) phylogenetic group represents the third largest phytoplasma cluster (Lee et al 2004) showing more than 98.6% 16S rRNA nucleotide identity among different strains (Lee et al 1998a). This group is naturally clustered in several different ecological niches (Lee et al 1998b) that could contribute to genetic drift

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Conclusion