Infectivity of nanovirus DNAs: induction of disease by cloned genome components of Faba bean necrotic yellows virus

Abstract

Circumstantial evidence suggests that the genome of Faba bean necrotic yellows virus (FBNYV), a nanovirus, consists of eight distinct, circular, single-stranded DNAs, each of about 1 kb and encoding only one protein. Here, the use of cloned full-length FBNYV DNAs for reproducing FBNYV-like symptoms in Vicia faba, the principal natural host of FBNYV, is reported. Characteristic symptoms of FBNYV infection were obtained in faba bean plants following biolistic DNA delivery or agroinoculation with all eight FBNYV DNAs. Although the eight different DNAs have been invariably detected in field samples infected with the various geographical FBNYV isolates, experimental infection with different combinations of fewer than eight DNAs also led to typical FBNYV symptoms. Even only five genome components, DNA-R, DNA-S, DNA-M, DNA-U1 and DNA-U2, were sufficient for inducing disease symptoms in V. faba upon agroinoculation. Symptomatic plants agroinoculated or bombarded with eight DNAs contained typical FBNYV virions; however, the virus was not transmitted by Aphis craccivora or Acyrthosiphon pisum, two efficient aphid vectors of FBNYV.

Reassortment and Concerted Evolution inBanana Bunchy Top VirusGenomes

“…In addition, based on the inoculation assay with cloned Faba bean necrotic yellow virus, DNA revealed a possible functional redundancy or complementation between distinctive nanovirus genomic components. It is possible that other components may have compensated for the function of DNA 2 and allowed DNA 2 to accumulate mutations (79).…”

Reconstitution of Authentic Nanovirus from Multiple Cloned DNAs

“…From FBNSV-infected V. faba tissue that had been frozen in 2000, total DNA was extracted according to a modified Edwards protocol described previously (15,54) with an additional step of phenol-chloroform extraction.…”

“…A prerequisite to studying viruses by reverse genetics is an artificial infection system, which has been accomplished only for FBNYV (54). Cloned viral DNAs were shown to be infectious, yet the virus thus obtained was not transmitted by aphid species known to be efficient vectors of FBNYV.…”

Advances in Small Isometric Multicomponent ssDNA Viruses Infecting Plants

“…All the Nanovirus DNAs code for only a single protein except, in BBTV, where the M-Rep encoding ORF contains additional 5 kDa protein of unknown function. Being multicomponent virus, the number of ssDNA components that are required for inducing disease was not known until 2006, when Timchenko et al [95] demonstrated infectivity of the cloned DNAs of FBNYV through agroinoculation. Only five DNA components DNA-R, DNA-S, DNA-M, DNA-U1 and DNA-U2 were enough to produce disease, however, the progeny viruses could not be transmitted through aphid vectors.…”

“…It was not known that how many components were necessary for causing disease. Timchenko et al [95] for the first time demonstrated infectivity of the FBNYV cloned DNAs. Ony five DNAs, DNA-R, DNA-S, DNA-M, DNA-U1 and DNA-U2 were sufficient to induce disease symptoms in Vicia faba following agroinoculation.…”