RESUMEN
Allexiviruses are economically important garlic viruses that are involved in garlic mosaic diseases. In this study, we characterized the allexivirus cysteine-rich protein (CRP) gene located just downstream of the coat protein (CP) gene in the viral genome. We determined the nucleotide sequences of the CP and CRP genes from numerous allexivirus isolates and performed a phylogenetic analysis. According to the resulting phylogenetic tree, we found that allexiviruses were clearly divided into two major groups (group I and group II) based on the sequences of the CP and CRP genes. In addition, the allexiviruses in group II had distinct sequences just before the CRP gene, while group I isolates did not. The inserted sequence between the CP and CRP genes was partially complementary to garlic 18S rRNA. Using a potato virus X vector, we showed that the CRPs affected viral accumulation and symptom induction in Nicotiana benthamiana, suggesting that the allexivirus CRP is a pathogenicity determinant. We assume that the inserted sequences before the CRP gene may have been generated during viral evolution to alter the termination-reinitiation mechanism for coupled translation of CP and CRP.
Asunto(s)
Proteínas de la Cápside/genética , Flexiviridae/genética , Ajo/virología , Regulación Viral de la Expresión Génica , Filogenia , Factores de Virulencia/genética , Emparejamiento Base , Secuencia de Bases , Evolución Biológica , Proteínas de la Cápside/metabolismo , Flexiviridae/clasificación , Flexiviridae/aislamiento & purificación , Flexiviridae/patogenicidad , Ajo/genética , Vectores Genéticos/química , Vectores Genéticos/metabolismo , Genoma Viral , Interacciones Huésped-Patógeno , Mutagénesis Insercional , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/virología , Potexvirus/genética , Potexvirus/metabolismo , Biosíntesis de Proteínas , ARN Ribosómico 18S/genética , ARN Ribosómico 18S/metabolismo , Alineación de Secuencia , Homología de Secuencia de Ácido Nucleico , Nicotiana/genética , Nicotiana/virología , Factores de Virulencia/metabolismoRESUMEN
Nucleotide sequences from the P1 gene and the 5' untranslated region of leek yellow stripe virus (LYSV), collected from several locations, were used to refine the phylogenetic relationships among the isolates. Multiple alignments revealed three distinct regions of insertions and deletions to classify LYSVs. In our phylogenetic analyses, the LYSV isolates separated into two major groups (N-type and S-type). S-type viruses had two large deletions compared to N-type viruses. Considering that the outgroup, onion yellow dwarf virus (OYDV) also has the sequences corresponding to the deletions in the S-type viruses, our study shows that the sequences missing in the S-type were present in the common ancestor of the N-type and S-type. In the phylogenetic trees, we found three distinct clades of isolates, from Uruguay (U), Okinawa (O) and Spain (Sp), suggesting that LYSVs have unique evolutionary histories depending on their garlic origins. The P1 gene of LYSV is thus quite suited to reflecting viral evolution, as recently suggested for other potyviruses.