Identificação e caracterização genômica de um isolado do Bean rugose mosaic virus

Abstract

The Bean rugose mosaic virus (BRMV) is a member of the genus Comovirus of the family Comoviridae, that infects leguminous plants. The complete genome of this virus had not yet been sequencenced. Comoviruses have two positive, single stranded genomic RNAs (RNA1 and RNA2), which are encapsidated into separate spherical virions. A virus isolate was mechanically inoculated in common bean cultivar Rio Tibagi, inducing symptoms of mosaic, blistering and leaf distortion. Indirect ELISA tests with antibodies for leguminous comoviruses were positives, and electron microscopic analysis revealed icosahedral particles approximately 28 nm in diameter in infected leaf samples. The virus transmission efficiency of Diabrotica speciosa was 40%. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis suggested the pathogen was a comovirus, as was confirmed after genomic partial sequencing. Eleven out of 29 soybean cultivars, and 17 out of 22 common bean cultivars showed symptoms after virus inoculation. The virus complete genome was sequenced consisting of two polyadenylated RNAs. RNA1 is 5909 nucleotides long encoding a single polypeptide of 1856 amino acids, with an estimated molecular weight of 210 kDa. The RNA1 polyprotein contains the polypeptides for viral replication and proteolytic processing. RNA2, that is 3644 nucleotides long, codes for a single 1097 amino acids polypeptide containing the movement protein and coat proteins. The complete nucleotide sequence of viral capsids (Small coat protein and Large coat protein) showed maximum identity of 54 and 61% with sequences from other Comovirus species. The isolate was identified as BRMV-Paraná, and based on sequencing data and on ICTV (International Committee on Taxonomy of Viruses) criteria, we propose BRMV as a distinct and definitive species in the Comovirus genus.