Molecular bases of the interactions between luteoviruses and aphids

Many viruses infecting vertebrates or plants are transmitted by arthropod vectors in a circulative manner. This requires the virus to cross epithelial cells of the gut and salivary glands, and to resist the potentially hostile environment of the vector. Fundamental knowledge regarding the strategies adopted by these persistent viruses to overcome the transmission barriers mentioned is surprisingly meagre. Here we describe the involvement of endosymbiotic bacteria in the transmission of potato leafroll virus by its aphid vector Myzus persicae. Symbionin, the major protein synthesized and released into the haemolymph by the bacterial endosymbiont, was found to determine the persistent nature of the luteovirus in its vector. The virus displays a strong affinity to this protein (M(r) = 63 000) which has high homology with the Escherichia coli heat shock protein groEL. The absence of symbionin in the haemolymph of aphids treated with antibiotics leads to rapid degradation of the major capsid protein of the virus and concomitant loss of infectivity.