Relative frequency dynamics and loading of beet necrotic yellow vein virus genomic RNAs during the acquisition by its vector Polymyxa betae

The beet necrotic yellow vein virus (BNYVV) is a multipartite virus with the highest number (up to five) of genomic segments among RNA viruses. Classified as a soil-borne virus, it is persistently transmitted by the protozoan Polymyxa betae. Previous studies have demonstrated that the relative frequency of the BNYVV genomic RNAs was modified depending on the host plant as well as the infected organ, resulting in distinct stoichiometric ratios between the viral RNAs. In this study, we investigate whether infection by the vector P. betae influences the relative abundance of BNYVV RNAs within the roots of the host plant Beta vulgaris. Furthermore, we examine the relative frequency of BNYVV genomic segments and the viral load of BNYVV at two different stages of P. betae's biological cycle: zoospore and resting spore. Our finding offers new insights into understanding the biology of this soil-borne virus and its vector. Notably, the variations in the relative accumulation of BNYVV RNAs observed in zoospores and resting spores, along with a higher viral load in zoospores compared to resting spores, invite consideration of the virus's replicative capacity within the vector.