Coat protein expression strategy of maize rayado fino virus and evidence for requirement of CP1 for leafhopper transmission

Abstract

Marafiviruses, including maize rayado fino virus (MRFV) and oat blue dwarf virus (OBDV), encode two carboxy co-terminal coat proteins, CP1 and CP2, which encapsidate the genome to form icosahedral virions. While CP2 expression is expected to be solely driven from a second start codon of a subgenomic RNA under a marafibox promoter sequence, the larger CP1 with an in-frame N-terminal extension relative to CP2 could potentially be expressed either by proteolytic release from the MRFV polyprotein or from subgenomic RNA translation. We examined MRFV CP expression strategy with a series of mutations in the CP coding region and identified mutants viable and nonviable for systemic plant infection. Polyprotein expression of MRFV CP1 was minimal. Mutants blocking CP2 expression failed to establish systemic infection, while mutants depleted in CP1 exhibited systemic infection and formation of virus-like particles but lost leafhopper transmissibility, indicating that CP1 is required for leafhopper transmission.