Genus Crinivirus

Type Species	Lettuce infectious yellows virus	(LIYV)

Distinguishing Features

Virions are shorter that 1000  nm and have two modal lengths (650-850 and 700-900  nm). The genome is a linear, positive sense, ssRNA 15.3-16  kb in size, divided into two molecules, both are needed for infectivity and separately encapsidated (Fig. 4). CP size of known members is rather uniform, ranging from 28 to 33 10³. LIYV RNA-1 is a bicistronic molecule comprising a 5- and 3-UTR of 97 and 219  nts, respectively. SPCSV and Tomato chlorosis virus (ToCV) have notably large ORFs for the CP duplicate (75-79 10³), unlike LIYV (52 10³). ORF1 codes for the replication-related proteins including RdRp, which is expressed via a putative ribosomal frameshift. ORF2 encodes a 32 10³ product with no similarity to any protein in databases. This ORF is similar in size and location to ORF2 of CTV and BYSV but the respective expression products are not related. RNA-2 has seven ORFs flanked by a 5-UTR of 326  nts and a 3-UTR of 187  nts. RNA-2 contains the five-gene module which, however, differs from that of members of the genus Closterovirus because of the insertion of an extra gene (ORF4) upstream of the CP gene. In all members of the genus the order of the CP and CPd ORFs is reversed. None of the members is transmissible by sap inoculation. Natural vectors are whiteflies (Bemisia, Trialeurodes) which transmit in a semi-persistent manner.

List of Species Demarcation Criteria in the Genus

The criteria demarcating species in the genus are:

	Particle size,
	Size of CP subunits, as determined by deduced amino acid sequence data,
	Serological specificity using discriminatory antibodies,
	Vector species and specificity,
	Magnitude and specificity of natural and experimental host range,
	Amino acid sequences of coat protein differing by more than 10%.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, CMI/AAB description numbers ( ), genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Abutilon yellows virus		(AbYV)
Cucurbit yellow stunting disorder virus		(CYSDV)
Lettuce chlorosis virus		(LCV)
Lettuce infectious yellows virus	[U15440, U15441]	(LIYV)
Sweet potato chlorotic stunt virus (Sweet potato sunken vein virus)	[X80995]	(SPCSV)
Tomato chlorosis virus		(ToCV)
Tomato infectious chlorosis virus		(TICV)

Tentative Species in the Genus

None reported.

Unassigned Species in the Family

None reported.

Phylogenetic Relationships within the Genus

Not available.

Similarity with Other Taxa

Virions of the genera Capillovirus, Trichovirus, and Vitivirus have the same particle morphology as those of the family Closteroviridae. However, the sequence of the CP of members of this family has little homology with that of CPs of the three above genera, and major differences exist in genome size and organization, and strategy of expression. Replication-associated proteins (RdRp, methyltransferase and helicase) contain signature sequences homologous to those of other taxa of the ”alpha-like“ supergroup of ssRNA viruses, the closest affinity being with the family Bromoviridae and the genera Tobravirus, Tobamovirus, and Hordeivirus. The replication strategy, based on polyprotein processing, translational frameshifting, and multiple sgRNA generation, closely resembles that of the families Coronaviridae and Arteriviridae. However, unlike closteroviruses, the RdRp of corona- and arteriviruses belongs to the “picorna-like” supergroup of polymerases. Hence, the transcriptional strategy of Closteroviridae follows the mechanism of other “alpha-like” viruses, and is dissimilar from the discontinuous, leader-primed transcription of corona- and arteriviruses.

Derivation of Names

Clostero: from Greek kloster, ‘spindle, thread’; crini from crinis, Latin for hair, from the appearance of the very long thread-like particles.