A Population Genetics Perspective on Geminivirus Infection

Area of Science:

• Plant virology
• Molecular biology
• Genetics

Background:

• Bipartite geminiviruses require two DNA components (DNA A and DNA B) for symptomatic infection.
• Previous research indicated DNA B-independent spread of DNA A, but its nuclear invasion and replication in systemic tissues remained unconfirmed.

Purpose of the Study:

• To demonstrate the autonomous invasion and replication of viral DNA A alone in systemic tissues of infected plants.
• To model the population dynamics of viral DNA A and DNA B spread and their frequencies during early systemic infection.

Main Methods:

• Selective accumulation of viral DNA components (DNA A and DNA B) during early systemic infection of Nicotiana benthamiana.
• Diagnosis of viral DNA in purified nuclei using specific hybridization for DNA A and DNA B, including dual-color staining.
• Population genetics evaluation and model computation comparing initial frequencies of viral DNA components with susceptible cell numbers.

Main Results:

• Viral DNA A alone was transported to upper leaves, invaded phloem nuclei, and replicated autonomously, independent of DNA B.
• Coinfection with DNA A and DNA B showed independent spread of both molecules, leading to stochastic distribution of infected nuclei.
• A simple relationship was found between initial viral DNA component frequencies and susceptible cell numbers during early infection.

Conclusions:

• Viral DNA A can invade and replicate in systemic tissues independently of DNA B, challenging previous assumptions about bipartite geminivirus infection requirements.
• The study provides a population genetics model explaining the distribution and frequencies of viral DNA components based on cell susceptibility and 'hit probabilities'.