Grapevine leafroll-associated virus 4

Grapevine leafroll-associated virus 4 is a recognized species in the genus Ampelovirus, family Closteroviridae, which comprises several genetically diverse variants denominated GLRaV-4 strains 4, 5, 6, 9, De, Car, Pr, and Ob. They are collectively referred to as “grapevine leafroll-associated virus 4-like viruses” (or GLRaV-4LVs). These viruses have been found associated with leafroll disease of grapevine, their sole host known to date. They are characterized by flexuous virions up to 1800 nm in length and a genome made up of a non-polyadenylated, single-stranded, positive-sense RNA molecule of 13.6–13.8 kb in size, depending on the particular strain/molecular variant. In spite of considerable differences in nucleotide content between molecular variants, the genome of all GLRaV-4LVs consists of seven open reading frames (ORFs), flanked by relatively short 5′ and 3′ untranslated regions (UTRs), respectively, that encodes six proteins (in the 5–3′ direction): the replication-associated polyprotein (expressed via +1 ribosomal frameshift of two partially overlapping ORFs), a small hydrophobic protein (p5), the HSP70 homologue (HSP70h), the 60K protein (p60), the viral coat protein (CP), and a protein of unknown function with a molecular mass of 23K (p23). GLRaV-4LVs are phloem-limited, nonmechanically transmissible, and distributed worldwide. Several mealybug and soft scale insect species mediate their short distance spread, while long-distance dissemination occurs primarily through infected propagating material.