The closely related citrus ringspot and citrus psorosis viruses have particles of novel filamentous morphology

Abstract

Some properties of the particles of citrus ringspot virus (CtRSV) and the related citrus psorosis-associated virus (CPsAV) are described. The particles of CtRSV have been reported to be sinuous linear structures about l0 nm in diameter and of two lengths (300 to 500 nm and 1500 to 2500 nm) representing 'top' and 'bottom' sedimentation components. We show that these particles are collapsed double-stranded forms of nucleocapsidlike, highly flexuous open circles formed of filaments 3 to 4 nm in diameter. Top-component filaments had contour lengths of 600 to 1000 nm, i.e. twice that reported for the corresponding collapsed form. Bottom-component filaments had contour lengths about four times longer than those of top-component filaments. The structures suggest that CtRSV represents a new genus (possibly family) related to the tenuiviruses. However, we failed to demonstrate any serological relationship between CtRSV and several tenuiviruses; moreover, the capsid protein sizes and host ranges are quite different. We offer the name Ophiovirus for the proposed new genus.

Recent advances in Citrus psorosis virus

“…In contrast, their 5 0 -terminal regions differ considerably in sequence. The circular morphology of CPsV virions suggests the possibility of a panhandle structure formed by base pairing between the two terminal regions of each RNA [19]. The first 75nt of the CPsV RNA1 terminal regions show 41 % complementarity, a value similar to that described for the RNAs of MiLBVV and of the lettuce bigvein varicosavirus [39].…”

“…Later on the basis of cross-protection tests [10], the similarity of symptoms and filamentous morphology between ringspot and psorosis isolates [19,42], and differences in number of particles of CPsV detected by immunosorbent electron microscopy (ISEM) using an antiserum to the isolate CPV-4 [43], it was suggested that ringspot and psorosis are variants of the same disease. The same conclusions were advanced by Da-Graça et al [7] and Rouag et al [56] respectively, who used serological and molecular comparisons.…”

“…Immunosorbent electron microscopy Antisera have been used to detect CPsV particles using immunosorbent electron microscopy (ISEM) [9,10,19,36,43]. ISEM technique was also applied for the efficient detection of CPsV in cross-protected citrus plants [33].…”

“…Ophiovirus (Family: Ophioviridae) have single stranded negative/possibly ambisense RNA genome (11.3-12.5 kb size) divided into 3-4 segments, each encapsidated in a single CP (43-50 kDa) forming filamentous virions about 3 nm in diameter, in shape of kinked (probably internally coiled) circles of at least two different contour lengths [19,73]. Since only one genus is currently recognized, the family description corresponds to the genus description.…”

“…CPsV virions are kinked filaments, 3-4 nm in diameter [19] that separate into two components during sucrose gradient centrifugation [9,18]. They consists of three single-stranded RNA (ssRNA) of negative polarity (vRNA) and a coat protein (CP) of * 48 kDa [5,58].…”