Small impact of the host plant physiological state on the genome formula of a nanovirus

The genome formula refers to the specific and reproducible pattern of relative accumulation of genome segments in within-host populations of viruses with segmented genomes. It has been proposed that the genome formula may have an adaptive function by allowing rapid adaptation of viral genes’ expression, through variation in their relative copy number, in response to a changing environment. Consistently, the faba bean necrotic stunt virus (FBNSV) genome formula has been demonstrated to be strongly dependent on the host genotype, since it changes significantly when the same viral isolate moves from one host species to another. However, the cellular environment of the virus can also be modulated by the growing conditions and/or stresses that impact on plant physiology. In this study, we thus cultivated Vicia faba plants under various biotic and abiotic stressing conditions with the aim of modifying the plant physiology in various and complementary ways and assess its potential impact on the genome formula. Although the plants exhibited phenotypes altered by the tested growing conditions, the total FBNSV accumulation was not impacted by the physiological changes in the plant except by aphid infestation which reduced it. Importantly, in contrast to the drastic change observed when switching hosts, the genome formula showed little or no variation across growing conditions for all the tested stressors. Our results thus indicate that the genome formula is marginally influenced by the physiological state of the host.