Insect vector–plant virus interactions associated with non-circulative, semi-persistent transmission: current perspectives and future challenges

• Insect vector transmission of plant viruses is a continuum of overlapping processes.
• Vector feeding and its interactions with virus and plant affect virus acquisition.
• NCSP viruses are retained in the maxillary stylets or foreguts of insect vectors.
• Virus retention is mediated by one of two virus-driven mechanisms.
• Understanding transmission entails a synthesis of plant–virus–vector interactions.

The non-circulative, semi-persistent (NCSP) mode of insect vector-mediated plant virus transmission is shaped by biological, molecular and mechanical interactions that take place across a continuum of processes involved in virion acquisition, retention and inoculation. Our understanding of the interactive roles of virus, insect vector, and plant associated with NCSP transmission is still evolving. Mechanisms exist that determine where and how virion acquisition (from the plant) and retention (in the insect vector) are achieved, with both processes being mediated by strategies involving viral capsid proteins, in some cases aided by non-capsid proteins. By contrast, mechanisms underlying virion inoculation (to the plant) remain poorly understood. Here, we review the established paradigms as well as fresh perspectives on the mechanisms of NCSP transmission.