Grapevine rupestris stem pitting-associated virus

Abstract

Grapevine rupestris stem pitting-associated virus (GRSPaV) is a member of the genus Foveavirus (family Betaflexiviridae, order Tymovirales). GRSPaV was discovered in 1998 from grapevines affected with Rupestris stem pitting, a widespread graft-transmissible disease among commercial grapevines worldwide. Later research has demonstrated that different genetic variants of GRSPaV are closely associated with, and likely the causal agent of, Rupestris stem pitting and vein necrosis. However, definitive proof for its etiological role in either disease is lacking. In the past two decades, much progress has been made in several fronts concerning this virus. Compelling evidence demonstrates that GRSPaV comprises a wide range of genetic variants differing extensively in genome sequence. To date, the complete or near-complete genomes of 15 isolates have been sequenced. Phylogenetic analyses revealed the existence of eight clusters of viral variants. Interestingly, the population structure of GRSPaV differs sharply depending on whether the infected plant is a rootstock or a scion cultivar. GRSPaV exists as a uniform population in rootstocks, with GRSPaV-1 being detected in Vitis riparia and its hybrids, while GRSPaV-SG1 detected in Vitis rupestris and its hybrids. In contrast, commercial grape cultivars are generally infected with mixtures of distinct variants. Quick, reliable, and sensitive methods have been developed to detect GRSPaV. The subcellular localization of proteins encoded by GRSPaV has been elucidated using fluorescent protein tagging and microscopy. The establishment of infectious GRSPaV clones has enabled diverse investigations on gene function and viral replication and, ultimately, the development of GRSPaV as a vector for various applications. It is hoped that GRSPaV would ultimately serve as an excellent model system for the study of members of the family Betaflexiviridae and perhaps many other viruses that infect woody fruit crops.