Molecular characterization of Olea europaea L. necrovirus transmission by fungal vectors

Abstract

Abstract OMMV is an olive infecting necrovirus, likely a recombinant between TNV-D, with which it shares a high identity in its coat protein (CP), and OLV-1. Design of specific primers to use in RT-PCR, allowed for the first time molecular discrimination of OMMV from TNV-D. RT-PCR application to an olive orchard survey revealed OMMV predominance. Its transmission by Olpidium brassicae was demonstrated here for the first time and further examined. OMMV wild-type, a natural non-transmissible OMMVL11 mutant containing two mutations, a construct OMMVWT/OMMVL11 and single mutants obtained by site-directed mutagenesis were found similarly infectious. Sequencing, homology modelling and transmissibility assays showed that the single mutation of Asn residue to Tyr in position 189 of the CP amino acid sequence was located internally in the particle and abolished virus-zoospore adsorption and transmissibility. This indicates that mutation altered CP conformation on zoospore recognition sites. These findings may have important epidemiological implications in the olive crop. Caracterização molecular da transmissão de Necrovirus (Tombusviridae) de Olea europaea L. por fungos vectores OMMV é um necrovirus que infecta a oliveira e que terá surgido a partir de recombinação entre TNV-D, com o qual compartilha uma elevada identidade na cápside proteica (CP), e OLV- 1. O desenho de ‘primers’ específicos para utilização em RT-PCR permitiu, pela primeira vez, a discriminação entre OMMV e TNV-D. A aplicação de RT-PCR a um olival revelou a predominância de OMMV. A transmissão por Olpidium brassicae foi aqui pela primeira vez demonstrada e examinada. OMMV ‘wild type’, um mutante natural OMMVL11 não transmissível contendo duas mutações e mutantes obtidos por mutagénese dirigida revelaram-se igualmente infecciosos. Sequenciação, modelagem por homologia e en