Molecular Characterization and Genomic Function of Grapevine Geminivirus A

Area of Science:

• Plant virology
• Molecular biology
• Genomics

Background:

• Grapevine geminivirus A (GGVA) is a plant pathogen affecting grapevines.
• Understanding GGVA pathogenicity and genetic diversity is crucial for disease management.

Purpose of the Study:

• To identify and characterize a new GGVA isolate and its associated defective genome.
• To investigate the pathogenicity of GGVA and its defective DNA in plants.
• To analyze the genetic diversity and molecular variation of GGVA isolates.

Main Methods:

• sRNA high throughput sequencing and Sanger sequencing for isolate identification.
• Construction of infectious clones for pathogenicity assays.
• Southern blotting and qPCR for viral DNA quantification.
• Transient expression assays and RNA silencing inhibition assays.
• Full-length genome sequencing, phylogenetic analysis, and molecular variation analysis.

Main Results:

• A new GGVA isolate (GGVA-17YM1) and defective genome (GGVA-D) were identified.
• Infection caused upward leaf curl and dwarfism in *Nicotiana benthamiana*.
• GGVA-D increased GGVA DNA accumulation; C2, C4, and V2 proteins were involved in pathogenicity and RNA silencing.
• 11 GGVA isolates and 9 defective DNA molecules were identified, showing two distinct phylogenetic branches.
• Analysis revealed SNPs, with transitions more frequent than transversions, and differential selection pressures on viral ORFs.

Conclusions:

• GGVA-D exacerbates GGVA pathogenicity by increasing viral DNA levels.
• Specific GGVA proteins play key roles in symptom induction and overcoming host defenses.
• GGVA exhibits significant genetic diversity with distinct evolutionary lineages.
• Understanding GGVA genetic variation and selection is vital for grapevine disease control.