A Population Genetics Perspective on Geminivirus Infection.

Abstract

The selective accumulation of both DNA components of a bipartite geminivirus, Abutilon mosaic virus, was recorded during early systemic infection of Nicotiana benthamiana plants. Purified nuclei were diagnosed for viral DNA using hybridization specific for DNA A or DNA B to detect these individual genome components either alone or both simultaneously by dual-color staining. Although this virus needs both components for symptomatic infection, DNA A alone was transported to upper leaves, where it was imported into phloem nuclei and replicated autonomously. The coinfection with DNA A and DNA B revealed an independent spread of both molecules, which resulted in a stochastic distribution of DNA A- and DNA A/B-infected nuclei. A population genetics evaluation of the respective frequencies was compared to a model computation. This elucidated a surprisingly simple relationship between the initial frequencies of the viral DNA components and the number of susceptible cells during the course of early systemic infection. For bipartite begomoviruses, DNA B-independent long-distance spread of DNA A has been described before, but it has never been shown whether viral DNA A alone invades nuclei of systemic tissues and replicates therein. This is demonstrated now for the first time. During infection with DNA A and DNA B, a similar solitary spread of DNA A can be recognized at early stages. We describe a population genetics model of how the hit probabilities of DNA A and DNA B for susceptible cells determine the relative frequencies of either genome component during the course of infection.