An RNA-dependent RNA polymerase gene of a distinct Brazilian tospovirus

Abstract

The tospoviral RNA-dependent RNA polymerases (RdRp), or L proteins, perform several conserved functions during virus replication in host cells. In this study, an L segment sequence of 9,040 bp from a new tospovirus (family Bunyaviridae) naturally infecting bean (Phaseolus vulgaris L.) plants was characterized. It encodes the largest RdRp gene known yet for this genus, with deduced 2932aa and a molecular mass of approximately 336 kDa. A Lysine-rich C-terminal extension was found, which apart from our isolate, was only recognized in another recently discovered tospovirus infecting Fabaceae, Soybean vein necrosis associated virus (SVNaV). Due to its distinct biological features and L protein-based phylogenetic analysis showing an almost equidistant position in comparison to Eurasian and American Tospovirus groups, as well as the clustering with SVNaV, we suggest the tentative name Bean necrotic mosaic virus for this unique isolate.

Characterization of Bean Necrotic Mosaic Virus: A Member of a Novel Evolutionary Lineage within the Genus Tospovirus

“…These results confirmed that BeNMV is particularly distinct from other characterized tospovirus species, as previously suggested using only the RNA-dependent RNA polymerase (RdRp) protein [15]. The correspondence between N and RdRp protein phylogeny suggests that both genes can be used to understand the phylogenetic relationships among tospoviruses, with the advantage of using a more conserved region (RdRp) and, consequently, simplifying the PCR-based strategies for detection of highly divergent new viruses.…”

“…As previously observed [13], [15], the American and Eurasian clades formed distinct monophyletic groups (bootstrap values of 98 and 98, respectively), and the Peanut chlorotic fan-spot virus (PCFSV) [28] and Groundnut yellow spot virus (PYSV) [29] (divergent viruses isolated from peanut) formed a monophyletic basal clade among tospoviruses. Crucially, the BeNMV was related to SVNaV, forming a well-supported monophyletic clade (bootstrap value of 93%), which was consistent with their pairwise distances (Table S2).…”

“…Concerning the L RNA sequence, we previously demonstrated [15] that this genome segment of BeNMV presents similar genomic organization to the RNA-dependent-RNA polymerase genes of other tospovirus species characterized so far. However, BeNMV L protein is unique, it has 2,932 aa and a molecular mass of 335.9 kDa, being the largest RdRp for this genus at the present date.…”

“…The BeNMV isolate was isolated in São Paulo State in Brazil [15] and maintained in P. pubescens by mechanical inoculation [34]. The other tospovirus isolates (TSWV, TCSV, GRSV and ZLCV) were maintained in D. stramonium .…”

“…[14] and common bean ( Phaseolus vulgaris L.) [15]; both of them clustered together and apart from the other tospovirus lineages. While the soybean-infecting tospovirus (Soybean vein necrosis-associated virus, SVNaV) genome has been completely sequenced [14], only the RNA-dependent RNA polymerase gene of the common bean tospovirus (Bean necrotic mosaic virus, BeNMV) has been determined [15]. No biological characterization has been reported for either virus.…”