The termini of a new citrus viroid contain duplications of the central conserved regions from two viroid groups

Abstract

A citrus viroid associated with dwarfing, CVdlIIA, has been sequenced and its 294 nucleotide residues can be arranged to form the typical rod-like secondary structure of other viroids with 71% of nucleotides base-paired. CVdIIIA has greatest sequence similarity with apple scar skin viroid (ASSVd; 69%) and has the central sequence which is conserved in the ASSVd group. CVdIIIA is the smallest member of the ASSVd group but contains the terminal conserved region shared by all viroids over 300 nucleotides. The two ends of CVdIIIA are highly unusual in that each end appears to be derived from the conserved central core region of a different viroid group.

Hop stunt viroid (HSVd) sequence variants from Prunus species: evidence for recombination between HSVd isolates.

“…species (Hammond et al, 1989 ;Puchta et al, 1991 ;Rezaian, 1990 ;Semancik et al, 1994 ;Stasys et al, 1995).…”

“…Indeed, this model is usually true in the case of inter-specific recombination (Hammond et al, 1989 ;Puchta et al, 1991 ;Rezaian, 1990). However, recent evidence from Stasys et al (1995) shows that exchanges can occur such that the upper and lower strands of a structural domain have different origins. They described a citrus viroid IIIA (CVdIIIa) isolate which contained an apple scar skin viroid (ASSVd)-derived upper CCR and a pear blister canker viroid (PBCVd) lower CCR.…”

Identification and molecular properties of a 306 nucleotide viroid associated with apple dimple fruit disease

“…1987) and with a 294 nt citrus viroid (Rakowski et aI., 1994;Stasys et al, 1995), respectively. Hereafter we will refer to this latter viroid as CVd-IIIb (Rakowski et al,i994), although it must be noted that a viroid with the same sequence, termed CVdlIIA, has also been reported (Stasys et al, 1995).…”

“…Hereafter we will refer to this latter viroid as CVd-IIIb (Rakowski et al,i994), although it must be noted that a viroid with the same sequence, termed CVdlIIA, has also been reported (Stasys et al, 1995). A more detailed comparison between ADFVd and CVd-IIIb showed three separate fragments with essentially identical sequences in both viroids.…”

“…This domain includes the TCR, which in these two viroids lacks the 3'-terminal U residue conserved in all other viroids containing this motif. It also includes the CCCGGAGGAAAAC sequence (except for an extra A) which in CVd-IIIb is an almost perfect duplication of part of the CCR lower strand of PSTVd and closely related viroids (Stasys et al, 1995). Conversely, the sequence CCGC-UAGUCG, a duplication of a portion of the CCR lower strand of the ASSVd viroid group found in the right-hand terminus of CVd-IIIb (Stasys et al, 1995), was not observed in ADFVd.…”