Vector-transmission of plant viruses and constraints imposed by virus–vector interactions

[Display omitted] •Each step of vector transmission constrains viral populations, from molecular to ecosystem scale.•Viruses must specifically interact with and efficiently encounter their vector.•The narrow transmission bottlenecks on viral population might be adaptive.•Vector transmission limits the viral host range to that of its vector.•The undisputable impact of the ecosystem structure on viral evolution remains terra incognita. Because plants are sessile and their cells protected by a cell wall, the contact transmission of plant viruses is very rare. Almost all plant viruses are transmitted by vectors, which can be insects, nematodes, mites or fungi. Although very efficient, this mode of transmission is not trivial and imposes numerous constraints on viruses. In this review we show that these constraints apply at all stages of the transmission process and at all scales, from the molecular to ecological interactions. We discuss several viral adaptations that likely reflect sophisticated means to alleviate these constraints and to maximize transmission, and we point at gaps and future directions in this field of research.