Received: 5 July, 2007. Accepted: 12 October, 2007. Invited Review Plant Viruses ©2007 Global Science Books Biological and Molecular Characterization of Olive latent virus 1 Maria do Rosário Félix 1,3* • Joana M. S. Cardoso 2,3 • Solange Oliveira 2,3 • Maria Ivone E. Clara 1,3 1 Departamento de Sanidade Animal e Vegetal, Universidade de Évora, Apartado 94, 7002-554 Évora, Portugal 2 Departamento de Biologia, Universidade de Évora, Apartado 94, 7002-554 Évora, Portugal 3 ICAM, Instituto das Ciências Agrárias Mediterrâneas, Universidade de Évora, Apartado 94, 7002-554 Évora, Portugal Corresponding author: * mrff@uevora.pt ABSTRACT Olive latent virus 1 (OLV-1) belongs to the Necrovirus genus, Tombusviridae family and is pathogenic to olive, citrus and tulip plants. It is easily mechanically transmissible to indicator plants causing necrotic lesions and can be transmitted through the soil into the plant roots in the absence of biological vectors. Infected cells contain virus aggregates, inclusions made up of excess of viral coded peptides and extensive vesiculation in the cytoplasm. The virions are isometric with ca. 30 nm, possess a monopartite single-stranded positive-sense RNA genome sized 3700 nt with 5 open reading frames (ORFs) and small inter cistronic regions. ORF 1 encodes a polypeptide with a molecular weight of 23 kDa and the read through of its amber stop codon results in ORF 1 RT that encodes the virus RNA dependent RNA polymerase with 82 kDa. ORF2 and ORF3 encode two small peptides, with 8 kDa and 6 kDa, respectively, which appear to be involved in the virus cell-to-cell movement. ORF 4 is located in the 3′ -terminal and encodes a protein with 30 kDa identified as the viral coat protein. The complete genomic sequences of two well characterized OLV-1 isolates (obtained from citrus and olive) are similar, revealing an overall nucleotide sequence identity of 95%. The electrophoretic profile of the dsRNAs recovered from infected tissues exhibits three major species with ca. 3.7, 1.5, and 1.3 kbp. Application of molecular techniques based on PCR and on dot blot hybridiza- tion has been successfully used for routine diagnosis of OLV-1 infections. _____________________________________________________________________________________________________________ Keywords: OLV-1, olive, molecular characterization, necrovirus, virus diagnosis Abbreviations: bp, base pair; CP, coat protein; dsRNA, double stranded RNA; ELISA, Enzyme linked immunosorbent assay; kb, kilo base; nt, nucleotide; OMMV, Olive mild mosaic virus; ORF, open reading frame; PCR, polymerase chain reaction; RdRp, RNA dependent RNA polymerase; RT-PCR, reverse transcription polymerase chain reaction; ssRNA, single stranded RNA; TNV-A, Tobacco necrosis virus A; TNV-D, Tobacco necrosis virus D CONTENTS INTRODUCTION...................................................................................................................................................................................... 170 VIRUS PROPERTIES................................................................................................................................................................................ 171 Biological and physico-chemical properties .......................................................................................................................................... 171 Cytopathology ....................................................................................................................................................................................... 171 VIRAL DISSEMINATION ........................................................................................................................................................................ 172 GENOME ORGANIZATION AND EXPRESSION.................................................................................................................................. 172 PHYLOGENETIC ANALYSIS ................................................................................................................................................................. 173 DIAGNOSIS .............................................................................................................................................................................................. 173 Dot blot hybridization............................................................................................................................................................................ 175 Reverse Transcription–Polymerase Chain Reaction .............................................................................................................................. 176 CONCLUDING REMARKS ..................................................................................................................................................................... 176 ACKNOWLEDGEMENTS ....................................................................................................................................................................... 176 REFERENCES........................................................................................................................................................................................... 176 _____________________________________________________________________________________________________________ INTRODUCTION Olive latent virus 1 has an apparently restricted natural host range. It was first detected in olive (Olea europaea L.) trees growing in Southern Italy that showed either no symptoms or occasional fasciation and bifurcation of stems (Gallitelli and Savino 1985). The virus was recovered by means of mechanical inoculation of olive flower extracts onto herba- ceous indicator plants where it caused, mainly, local lesions (Table 1). Following virus purification and characterization it was revealed that it had physico-chemical properties simi- lar to those of necroviruses but differed serologically from them. Thus, it was proposed as a new species of the Necro- virus genus (Gallitelli and Savino 1985; Martelli et al. 1996). In 1995, similar isolates were found in olive in Jor- dan, in Portugal (Félix and Clara 2002) and successively in other countries of the Middle East, being likely that the virus is widely distributed wherever the crop is grown (Table 1). However, its economic importance is yet to be ascertained. In addition to olive, in Turkey OLV-1 was detected in several citrus species where it appeared symptom less, as well as, in many plants affected by the ‘chlorotic dwarf dis- ease’, that is characterized by leaf malformation, chlorotic flecking in the interveinal areas and oak leaf patterns (Çinar et al. 1993; Martelli et al. 1996). In Portugal several isolates were obtained from Galega vulgar, Cordovil de Serpa and Verdeal Alentejana cultivars showing low vigor, leaf chlo- rosis (Fig. 1A) and, occasionally, no symptoms. Recently, a virus recovered from tulips, in Japan, exhibiting mottling