The Master Rep Concept in Nanovirus Replication: Identification of Missing Genome Components and Potential for Natural Genetic Reassortment

Abstract

Faba bean necrotic yellows virus (FBYNV), Milk vetch dwarf virus (MDV), and Subterranean clover stunt virus (SCSV) are nanoviruses that infect leguminous plants. From MDV- and SCSV-infected tissue we identified viral DNAs that encode a replication initiator protein (Rep), essential for replication of the multiple circular single-stranded DNAs of these viruses. These previously undescribed Rep proteins of MDV and SCSV are strikingly similar in sequence and functionally equivalent to the master Rep protein of FBYNV. Moreover, we demonstrated that the master Rep proteins of the three viruses are able to trigger replication of heterologous nanovirus DNAs. Such cross-species replication may reflect a considerable potential for genetic reassortment among nanoviruses in nature and be of significance for their evolution.

Reassortment and Concerted Evolution inBanana Bunchy Top VirusGenomes

“…In addition, more than one Rep-encoded component may be associated with virus infection in nanoviruses (22,29,30,39,63). Only one of these Rep genes, master Rep, can directly replicate non-self-replicable components, and remaining Rep-encoded components are considered to be satellite viruses (29,78,80). Among BBTV, DNA 1 encodes the master Rep, and several additional Rep-encoded components have been reported in the Asian strains (29,30,88,91).…”

Molecular Characterization of Geographically Different Banana bunchy top virus Isolates in India

“…It is transmitted by banana black aphid (P. nigronervosa) in a persistent manner. The genome of BBTV consists of at least six integral components each approximately 1 kb in size (BBTV DNA-R, -S, -M, -C, -N and -U) [3,5,17,18,21]. BBTV DNA-R encodes a master replication initiation protein (Rep) and DNA-S encodes a viral coat protein (CP) for encapsulation (Karan et al [9].…”

Advances in Small Isometric Multicomponent ssDNA Viruses Infecting Plants

“…The replication of Babuvirus and Nanovirus is through rolling circle mechanism. In many of the Nanovirus or Babuvirus, several ssDNA components have been shown to encode Rep related proteins, of which only one Rep component that controls replication of other ssDNA components is known as master Rep (M-Rep) [94]. Replication of the DNAs is facilitated and enhanced by the action of 19 kDa Clink, a cell cycle linked protein [4].…”

“…SCSV has a functionally divided genome composed of multiple circular, ssDNA molecules of about 1 kb, each of which are encapsidated in a separate particle with a short complementary primer sequence [13,14]. The sequence of eight circular, ssDNA components of SCSV has been determined so far [8,94]. All components contain a single ORF in sense direction and a stable stem-loop structure in the noncoding region.…”

“…MDV-C7 and FBNYV-C6 each encode a 15 kDa protein, which was not present in SCSV and BBTV. C11 (DNA-R) encoded the M-Rep, required for replication of all the other genomic DNAs [94]. Based on the sequence similarity between proteins of different nanoviruses, C4, C6, C8 and C9 were identified to encode Clink, NSP, MP and CP, respectively [98].…”