Mechanistic Insights into Potyviral and Cucumoviral Subversion of Plant Resistance

Potyviruses and cucumoviruses (exemplified by cucumber mosaic virus (CMV)) are highly divergent taxa of plant-infecting positive-sense RNA viruses. However, they face similar challenges. They must overcome host antiviral resistance mechanisms, for example, RNA silencing or resistance mediated by the phytohormone salicylic acid, and they must do this across a very diverse range of host species. Although in some hosts potyviruses and CMV are seedborne, they are predominantly transmitted by aphid vectors. Both have acquired mechanisms for subverting host defences, particularly those controlled by jasmonic acid, to manipulate vector behaviour and increase transmission. This article compares how CMV and potyviruses took distinct evolutionary paths to overcome these common challenges. Potyviruses diverged into numerous distinct viral species to exploit different hosts and co-opted many gene products, including P1, HC-Pro, NIa, VPg, 6K2 and NIb, to effector roles. In contrast, CMV strains show less divergence but still exploit wide host ranges, and predominantly use the 2b counter-defence protein for subverting and manipulating host responses.