SOME PROPERTIES OF FIG LATENT VIRUS 1, A NEW MEMBER OF THE FAMILY FLEXIVIRIDAE

Abstract

A virus with filamentous particles ca. 700 nm long, denoted Fig latent virus 1 (FLV-1) is widespread in Apulian (southern Italy) fig orchards, in trees showing or not mosaic symptoms and in symptomless seedlings. This virus was transmitted by sap inoculation to a very restricted range of herbaceous hosts without inducing apparent symptoms. It was successfully purified from root tissues of infected figs. A virus-specific antiserum raised in rabbits, proved useful for its detection in fig leaf dips by immunosorbent electron microscopy. The cytology of infected cells was little affected. Bundles of filamentous particles were observed in the cytoplasma of parenchyma cells of infected fig trees and seedlings. The viral genome is a single-stranded positive-sense RNA with an estimated size of ca. 8,000 nt, 6,620 of which have been sequenced, starting from the polyadenylated 3’ terminus. Genomic RNA consists of four open reading frames encoding, in the 5’?3’ direction, the replication-associated proteins (ORF 1), a 43 kDa putative movement protein (ORF 2), the 46 kDa coat protein (ORF 3), and a 12 kDa protein with nucleic acid binding properties. The viral genome structure and organization resembles that of members of the genus Trichovirus, family Flexiviridae and, indeed, FLV- 1 clusters with trichoviruses in phylogenetic trees constructed with coat protein sequences. However, a distinct difference with all members of the genus rests with the size of the coat protein subunits (46 versus 22-27 kDa) and the presence of ORF 4, which is present only in three tentative species of this genus.