Multiple functions of capsid proteins in (+) stranded RNA viruses during plant-virus interactions

In addition to providing a protective shell for genomic RNA(s), the coat (capsid) proteins (CPs) of plus-stranded RNA viruses play a variety of other functions that condition the plant-virus relationship. In this review we outline the extensive research progress that has been made within the last decade on those CP characteristics that relate to virus infectivity, pathogenicity, symptom expression, interactions with host factors, virus movement, vector transmission, host range, as well as those used to study virus evolution. By discussing the examples among a variety of plant RNA viruses we show that in addition to general features and pathways, the involvement of CPs may assume very distinct tasks that depend on the particular virus life style. Research perspectives and potential applications are discussed at the end.