Generation of Variability in Chrysodeixis includens Nucleopolyhedrovirus (ChinNPV): The Role of a Single Variant

Abstract

The mechanisms generating variability in viruses are diverse. Variability allows baculoviruses to evolve with their host and with changes in their environment. We examined the role of one genetic variant of Chrysodeixis includens nucleopolyhedrovirus (ChinNPV) and its contribution to the variability of the virus under laboratory conditions. A mixture of natural isolates (ChinNPV‑Mex1) contained two genetic variants that dominated over other variants in individual larvae that consumed high (ChinNPV-K) and low (ChinNPV-E) concentrations of inoculum. Studies on the ChinNPV‑K variant indicated that it was capable of generating novel variation in a concentration-dependent manner. In cell culture, cells inoculated with high concentrations of ChinNPV-K produced OBs with the ChinNPV-K REN profile, whereas a high diversity of ChinNPV variants was recovered following plaque purification of low concentrations of ChinNPV-K virion inoculum. Interestingly, the ChinNPV-K variant could not be recovered from plaques derived from low concentration inocula originating from budded virions or occlusion-derived virions of ChinNPV-K. Genome sequencing revealed marked differences between ChinNPV-K and ChinNPV-E, with high variation in the ChinNPV-K genome, mostly due to single nucleotide polymorphisms. We conclude that ChinNPV‑K is an unstable genetic variant that is responsible for generating much of the detected variability in the natural ChinNPV isolates used in this study.

Empirical estimates of the mutation rate for an alphabaculovirus

“…Whether intricate relationships between genetic variants that complement each other are common or evolutionarily stable remains to be seen, but such relationships would help to explain the genetic diversity often seen within alphabaculovirus populations. Recently, a novel strain of Chyrosodeixis includens nucleopolyhedrovirus was described, which generates high levels of genetic variation when it is at low frequency in mixed infection [ 46 ]. If such strains with high mutation rates occur in other baculoviruses, their existence may help explain the high genetic variation often observed in baculovirus populations, even if they are rare genotypes.…”

Coocclusion of Helicoverpa armigera Single Nucleopolyhedrovirus (HearSNPV) and Helicoverpa armigera Multiple Nucleopolyhedrovirus (HearMNPV): Pathogenicity and Stability in Homologous and Heterologous Hosts

“…Replication in a particular host also affects virion composition as both budded virus and ODVs can be contaminated by host-specific proteins [70]. Spontaneous generation of genetic diversity has also been reported in nucleopolyhedrovirus variants, including HearSNPV, especially at low inoculum doses [18,71]. However, the high inoculum doses used in the present study would likely have obfuscated the spontaneous generation of variability, although we did not address this issue in the present study.…”

Nucleopolyhedrovirus Coocclusion Technology: A New Concept in the Development of Biological Insecticides

“…Indeed, a recent estimate of the rate of mutation during replication, in the absence of selection bias, indicated that AcMNPV has a mutation rate of approximately 1 × 10 –7 substitutions per nucleotide per round of copying, typical of the very low mutation rates observed in DNA viruses ( Boezen et al, 2021 ). In spite of this, single nucleotide polymorphisms are present at high frequency (∼10 –3 ) in NPV populations ( Chateigner et al, 2015 ; Masson et al, 2021 ), and some variants are capable of generating remarkable levels of variation spontaneously during replication, a process that is particularly apparent when host larvae are inoculated with low doses of OBs ( Baillie and Bouwer, 2013 ; Aguirre et al, 2021 ).…”