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Abstract
Turnip mosaic virus (TuMV, family Potyviridae) and cauliflower mosaic virus (CaMV, family Caulimoviridae) are transmitted by aphid vectors. They are the only viruses shown so far to undergo transmission activation (TA) immediately preceding plant-to-plant propagation. TA is a recently described phenomenon where viruses respond to the presence of vectors on the host by rapidly and transiently forming transmissible complexes that are efficiently acquired and transmitted. Very little is known about the mechanisms of TA and on whether such mechanisms are alike or distinct in different viral species. We use here a pharmacological approach to initiate the comparison of TA of TuMV and CaMV. Our results show that both viruses rely on calcium signaling and reactive oxygen species (ROS) for TA. However, whereas application of the thiol-reactive compound N-ethylmaleimide (NEM) inhibited, as previously shown, TuMV transmission it did not alter CaMV transmission. On the other hand, sodium azide, which boosts CaMV transmission, strongly inhibited TuMV transmission. Finally, wounding stress inhibited CaMV transmission and increased TuMV transmission. Taken together, the results suggest that transmission activation of TuMV and CaMV depends on initial calcium and ROS signaling that are generated during the plant’s immediate responses to aphid manifestation. Interestingly, downstream events in TA of each virus appear to diverge, as shown by the differential effects of NEM, azide and wounding on TuMV and CaMV transmission, suggesting that these two viruses have evolved analogous TA mechanisms.
Highlights
Viruses are obligate intracellular parasites and depend completely on the machinery and metabolism of a host cell to accomplish the different steps of their infection cycle
Transmissible complexes are composed of the virus particle and the helper component, a viral non-structural protein mediating binding of the virion to the vector mouthparts
Recent studies on two non-circulative aphid-transmitted viruses using the helper strategy, cauliflower mosaic virus (CaMV, family Caulimoviridae) and turnip mosaic virus (TuMV, family Potyviridae), showed that vector feeding activity induces formation of transmissible complexes in infected plant cells within seconds[6,7,8]. This suggests that these two viruses switch transiently from a replication/accumulation mode to a transmission mode, a phenomenon named transmission activation (TA)[9]
Summary
Viruses are obligate intracellular parasites and depend completely on the machinery and metabolism of a host cell to accomplish the different steps of their infection cycle. Recent studies on two non-circulative aphid-transmitted viruses using the helper strategy, cauliflower mosaic virus (CaMV, family Caulimoviridae) and turnip mosaic virus (TuMV, family Potyviridae), showed that vector feeding activity induces formation of transmissible complexes in infected plant cells within seconds[6,7,8]. This suggests that these two viruses switch transiently from a replication/accumulation mode to a transmission mode, a phenomenon named transmission activation (TA)[9]. The initial calcium and/or ROS fluctuations trigger downstream reactions that establish PAMP-triggered immunity (PTI)[19]
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