Transmission activation of potyviruses

Abstract

BGPI : équipe 2Potyviruses are transmitted by aphids, like hundreds of other plant viruses, in a non-circulative manner, and following the molecular strategy called "transmission helper component". This indicates that when aphids feed on an infected plant, the transmitted virus particles attach within seconds to the stylets (mouthparts of aphids), and are transported to a new host plant. The connection between the Potyvirus virions and the stylets is not direct, a transmission helper factor, the viral protein Helper Component Protease (HC-Pro), intervenes by creating the molecular link between virions and stylets. The Caulimovirus Cauliflower mosaic virus, another non-circulative virus using a different transmission helper component, P2, responds to the presence of aphid vectors on the plant by forming only then transmissible P2-virion complexes. This strategy, called "Transmission Activation (TA)", controls CaMV transmission. Here, the transmission of Potyviruses has been tested in order to determine if these viruses also follow this strategy. The pathosystems tested are turnip/Turnip mosaic virus, lettuce/Lettuce mosaic virus and tobacco/Potato Virus Y. Aphid transmission tests with green peach aphids (Myzus persicae) were carried out using infected protoplasts as virus source that were incubated with various substances before the transmission tests. The results showed that a blocker of calcium signaling, Lanthanum(III) chloride (LaCl3), inhibited transmission while the reactive oxygen species (ROS), hydrogen peroxide (H2O2), activated it. Western blotting established that LaCl3 inhibited and H2O2 induced formation of intermolecular cystein bonds linking HC-Pro oligomers. Taken together, our results show that Potyvirus transmission can be activated, that calcium signaling and ROS are involved in it and that it correlates with oxidation of HC-Pro. Thus, Potyviruses are a second example for the TA phenomenon, and a model of Potyvirus transmission is presented