ICTV Virus Taxonomy Profile: Closteroviridae

Abstract

Viruses in the family Closteroviridae have a mono-, bi-or tripartite positive-sense RNA genome of 13-19 kb, and non-enveloped, filamentous particles 650-2200 nm long and 12 nm in diameter. They infect plants, mainly dicots, many of which are fruit crops. This is a summary of the ICTV Report on the family Closteroviridae, which is available at ictv. global/ report/ closteroviridae.

Molecular Characterization of the Complete Coding Sequence of Olive Leaf Yellowing-Associated Virus

“…Closteroviridae members have among the largest genomes of plant viruses (13,000 to nearly 19,000 nt) composed of one, two or three positive-sense, single-stranded RNA segments [ 14 ]. Currently there are four recognized genera in the family, Closterovirus , Ampelovirus , Velarivirus and Crinivirus .…”

“…In addition, another characteristic of the family is the presence of a homolog to the cellular HSP70h and, in most members, the presence of a diverged, duplicate copy of the capsid protein called minor capsid protein (CPm). The genus demarcation criteria in the family include phylogenetic relationships in the RdRp, CP, HSP70h aa sequences, the identity of vectors, and the number of genomic RNAs, number and organization of ORFs and virion length [ 14 ]. In the currently recognized taxonomy, seven Closteroviridae species remain unassigned to a genus, including OLYaV, for which only partial sequences were available until now.…”

“…The lack of CPm is another interesting feature, as it is known that this protein is common to Closteroviridae members and encapsidates the 600–700 5′-terminal nucleotides, and are believed to contribute to the initiation of encapsidation. There are however some exceptions, as the ampeloviruses with the smallest genomes, such as GLRaV-4 or PMWaV-1, do not appear to possess a CPm [ 14 ]. How these viruses initiate their encapsidation without CPm remains to be studied.…”

“…In addition, studies of OLYaV HSP70 gene diversity revealed a high divergence in this region of samples collected in clonal germplasm repositories in California and Greece [ 5 , 12 ]. To date OLYaV remains as an unassigned species in the family Closteroviridae because more biological and molecular data is needed for its classification and because the available partial genome data do not allow one to clearly assign it to any of the genera in the family [ 14 , 15 ]. Initially, the closterovirus name was assigned to an unusual group of elongated plant viruses [ 16 ], reflecting their peculiar morphological characteristics as compared to other elongated plant viruses known at that moment.…”

“…Thus, the family Closteroviridae is now divided into four genera; Closterovirus , Ampelovirus , Crinivirus and the relatively recently created genus Velarivirus , in which forty-nine species are classified. Seven other species in the family remain unassigned to a genus: Blueberry virus A (BVA), Actidinia virus 1 (AV1) and Persimmon virus B , for which complete genomes are available; Mint vein banding-associated virus (MVBaV) and OLYaV, for which only partial genomic sequences are available; and Alligatorweed stunting virus and Megakepasma mosaic virus without available nucleotide sequences [ 14 ]. Among these species, OLYaV is most closely related to PVB [ 22 ] and AV1 [ 23 ], as phylogenetic analyses based on the partial OLYaV genomic sequence cluster these three species together.…”