Regulation of Positive-Strand Accumulation by Capsid Protein During Brome mosaic virus Infection In Planta

Area of Science:

• Virology
• Molecular Biology
• Plant Pathology

Background:

• (+)-strand RNA viruses accumulate progeny (+)-strands 100-fold over (-)-strands.
• Brome mosaic virus (BMV) coat protein (CP) translation is linked to increased (+)-strand accumulation.

Purpose of the Study:

• To investigate whether BMV CP stimulates (+)-strand accumulation via direct RNA replication regulation or RNA stabilization through encapsidation.
• To determine the role of CP binding and dimerization in (+)-strand accumulation.

Main Methods:

• Analysis of BMV progeny RNA in *Nicotiana benthamiana* plants.
• Engineering mutations in CP open reading frames to assess binding and dimerization.
• Complementing CP in trans to rescue (+)-strand accumulation defects.

Main Results:

• RNA3 variants lacking WT CP severely reduced (+)-strand accumulation, rescuable by trans-complemented CP.
• N-terminal CP deletion (preventing RNA binding) reduced (+)-strand accumulation and increased (-)-strand accumulation.
• C-terminal CP mutation (affecting dimerization) decreased (+)-strand accumulation without affecting (-)-strand accumulation.
• Movement protein-coding region sequences contribute to (+)-strand accumulation via packaging signals.

Conclusions:

• RNA encapsidation is a significant factor in BMV RNA intracellular accumulation.
• CP's role in encapsidation is crucial for efficient (+)-strand accumulation.
• Specific CP domains and RNA sequences influence viral RNA accumulation.