The roles and mechanisms of helper component proteins encoded by potyviruses and caulimoviruses

The requirement for helper component(s) (HC) facilitating virus transmission by living organisms, termed vectors, is characteristic of plant viruses in several genera, potyviruses (genus Potyvirus, family Potyviridae) and caulimoviruses (genus Caulimovirus, family Caulimoviridae) being the most intensively studied groups of viruses. The potyviral HC-Pro fulfils several functions, including aphid transmission, long-distance movement and suppression of post-transcriptional gene silencing. The HC of Cauliflower mosaic virus plays an important role in aphid transmission, whereas no direct role in viral infectivity has so far been attributed to this protein. This review shows the current knowledge of major functions of HCs encoded by potyviruses and caulimoviruses.