Functional analysis of the grapevine virus A genome

Area of Science:

• Plant virology
• Molecular biology
• Genetics

Background:

• Grapevine virus A (GVA) has five open reading frames (ORFs), with only the coat protein ORF definitively identified.
• The functions of other GVA ORFs have been inferred through sequence homology.

Purpose of the Study:

• To experimentally determine the function of each GVA ORF.
• To elucidate the roles of GVA genes in viral replication, gene expression, symptom development, and movement.

Main Methods:

• Utilized a previously constructed full-length infectious clone of GVA.
• Introduced specific mutations into each of the five ORFs.
• Assessed the impact of mutations on viral replication, gene expression, symptomology, and systemic movement.

Main Results:

• Mutations in ORF 1 completely abolished viral RNA replication.
• Mutations in ORF 2 did not significantly affect viral replication, gene expression, symptoms, or movement.
• Mutations in ORFs 3 and 4 restricted the movement of GVA within the plant.
• Mutations in ORF 5 resulted in an asymptomatic virus and partially restricted its movement.

Conclusions:

• ORF 1 is critical for Grapevine virus A RNA replication.
• ORFs 3, 4, and 5 play significant roles in GVA's cell-to-cell and systemic movement.
• ORF 5 influences symptom development, with mutations leading to asymptomatic infections.