Mapping viral functional domains for genetic diversity in plants

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Cucumber mosaic virus (CMV) exhibits significant in-host genetic diversity among its numerous isolates.
• Distinctive features of the Fny and LS strains offer a model for studying viral genetic variation.
• Understanding viral control elements is crucial for managing CMV evolution and spread.

Purpose of the Study:

• To genetically map viral control elements responsible for in planta genetic variation in CMV.
• To identify specific regions within CMV RNAs that regulate mutation frequency and polymorphism.
• To elucidate the role of the 2b gene in controlling viral mutant populations.

Main Methods:

• Comparative genetic analysis of Fny and LS CMV strains.
• Fine mapping of viral RNA regions associated with mutation frequency.
• Identification of polymorphism hotspots within viral genomes.
• Analysis of the 2b gene's function in regulating viral mutants.

Main Results:

• Both RNA 1 and RNA 2 were identified as controllers of genetic diversity.
• Mutation frequency control elements were localized to the first 596 amino acids of RNA 1.
• The 2a/2b overlapping region of the 2a protein also influences viral genetic variation.
• The 3' nontranslated region (NTR) of RNA 3 is a major hotspot for genetic polymorphism.
• The CMV 2b gene, a viral suppressor of gene silencing, modulates fixed mutant abundance in a host-dependent manner.

Conclusions:

• Specific regions within CMV RNAs, including RNA 1 and RNA 3's 3' NTR, are critical for controlling viral genetic diversity.
• The 2b gene plays a significant role in regulating the population dynamics of CMV mutants through a host-dependent mechanism.
• These findings provide insights into the molecular mechanisms driving CMV evolution and adaptation.