Characterization of a putative novel nepovirus from Aeonium sp.

A virus was isolated from potted plants of an unidentified species of Aeonium, a succulent ornamental very common in Southern Italy, showing chlorotic spots and rings on both leaf surfaces. It was successfully transmitted by sap inoculation to a limited range of hosts, including Nicotiana benthamiana which was used for ultrastructural observations and virus purification. Virus particles are isometric, ca. 30nm in diameter, have a single type of coat protein (CP) subunits 54kDa in size, that encapsidate single-stranded positive-sense RNA species of 7549 (RNA1) and 4010 (RNA2) nucleotides. A third RNA molecule 3472 nts in size entirely derived from RNA2 was also found. The structural organization of both genomic RNAs and the cytopathological features were comparable to those of nepoviruses. In addition, amino acid sequence comparisons of CP and the Pro-Pol region (a sequence containing parts of the proteinase and polymerase) with those of other nepoviruses showed that the Aeonium virus belongs to the subgroup A of the genus Nepovirus and is phylogenetically close to, but serologically distinct from tobacco ringspot virus (TRSV). Based on the species demarcation criteria for the family Secoviridae, the virus under study appears to be a novel member of the genus Nepovirus for which the name of Aeonium ringspot virus (AeRSV) is proposed.