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Phloem Protein Partners of Cucurbit aphid borne yellows virus: Possible Involvement of Phloem Proteins in Virus Transmission by Aphids

¹INRA Université de Strasbourg, UMR SVQV, 28 rue de Herrlisheim BP 20507, 68021 Colmar, France; ²CNRS-IBMP Département de Virologie, 12 rue du Général Zimmer, 67084 Strasbourg, France; ³INRA UR501 Laboratoire de Biologie Cellulaire, Institut Jean Pierre Bourgin, route de Saint-Cyr, 78026 Versailles, France; ⁴INRA UR1268 Biopolymères, Interactions Assemblages, rue de la Géraudière BP 71627, 44316 Nantes, France; ⁵Plateforme Protéomique de l'Esplanade, 15 rue Descartes, 67084 Strasbourg, France

Poleroviruses are phytoviruses strictly transmitted by phloem-feeding aphids in a circulative and nonpropagative mode. During ingestion, aphids sample virions in sieve tubes along with sap. Therefore, any sap protein bound to virions will be acquired by the insects and could potentially be involved in the transmission process. By developing in vitro virus-overlay assays on sap proteins collected from cucumber, we observed that approximately 20 proteins were able to bind to purified particles of Cucurbit aphid borne yellows virus (CABYV). Among them, eight proteins were identified by mass spectrometry. The role of two candidates belonging to the PP2-like family (predominant lectins found in cucurbit sap) in aphid transmission was further pursued by using purified orthologous PP2 proteins from Arabidopsis. Addition of these proteins to the virus suspension in the aphid artificial diet greatly increased virus transmission rate. This shift was correlated with an increase in the number of viral genomes in insect cells and with an increase of virion stability in vitro. Surprisingly, increase of the virus transmission rate was also monitored after addition of unrelated proteins in the aphid diet, suggesting that any soluble protein at sufficiently high concentration in the diet and acquired together with virions could stimulate virus transmission.