Tomato chlorotic dwarf viroid: an evolutionary link in the origin of pospiviroids

Abstract

Over 40 isolates of potato spindle tuber viroid (PSTVd) have been reported from potato, other Solanum species and greenhouse tomato. These isolates have sequence similarities in the range 95-99 %. A viroid which caused chlorotic leaves and severe dwarfing of plants in greenhouse tomato crops was detected. The viroid was found to hybridize readily with PSTVd probes. It migrated faster than PSTVd in return-polyacrylamide gel electrophoresis and was not amplified in RT-PCR by a primer pair based on the lower strand of the central conserved region of PSTVd. Nucleotide sequencing of the viroid indicated that it is a circular RNA of 360 nt, with less than 90 % sequence similarities with PSTVd isolates. The Variable domain (V) has less than 60 % and the Terminal Right domain less than 90 % sequence similarity, while the remainder of the molecule has greater than 97 % similarity with PSTVd. Because of its less-than 90 % sequence similarities, unique V domain, lack of seed-transmission and lack of cross-protection by PSTVd, the viroid from tomato is proposed to be a distinct viroid species (tomato chlorotic dwarf viroid ; TCDVd) which also differs from two viroids infecting tomato in nature. TCDVd may be an evolutionary link in the development of crop viroids, with Mexican papita viroid as the ancestral viroid.

Current status of viroid taxonomy

“…In their initial characterization of TCDVd, Singh et al [59] reported that, in contrast to PSTVd, the former was not seed-transmissible; this was the case for both potato (two varieties) and five solanaceous indicator species that could be infected with TCDVd by mechanical inoculation. A later publication from the same group [58] showed that TCDVd is actually transmissible through tomato seed.…”

“…Comparatively little is currently known about the sequence motifs that control viroid's ability to replicate and move systemically in different hosts (e.g., [69]); thus, until this situation improves, caution is necessary in evaluating evidence for differences in the biological properties of viroids. At present, the strongest evidence of biological differences between PSTVd and TCDVd is the failure of the former to cross-protect tomato against challenge inoculation with the latter [59].…”

First report of a Tomato chlorotic dwarf viroid disease on tomato plants in Japan

“…Lane 1, diseased tomatoes in a field at Hiroshima Prefecture; 2, graft-inoculated tomato; 3, mechanically inoculated tomato; 4, mock-inoculated tomato; 5, distilled water control; M, 100-bp size marker DDBJ accession no. AB329668) sharing 98% identity with that of the TCDVd isolate (AF162131) previously reported from Canada (Singh et al 1999). Five nucleotides were substituted, 165 (T ?…”

“…In solanaceous plants such as tomatoes (Solanum lycopersicon) and potatoes (S. tuberosum), the following six species of pospiviroids have been isolated worldwide from naturally infected crops: Citrus exocortis viroid (CEVd) (Mishra et al 1991); Columnea latent viroid (CLVd) (Hammond et al 1989); PSTVd; Tomato apical stunt viroid (TASVd) (Spieker et al 1996); Tomato chlorotic dwarf viroid (TCDVd) (Singh et al 1999(Singh et al , 2006Verhoeven et al 2004); and Tomato planta macho viroid (TPMVd) (Galindo et al 1982).…”

“…To identify the pathogenic viroid, the following two primer sets were employed for reverse transcription (RT) and a polymerase chain reaction (PCR) to detect PSTVd according to previous reports of tomato viroid diseases (Singh et al 1999;Spieker et al 1996) using (1) RT and reverse primer 3P (5 0 -CCGGATCCCTGAAGCGCTCCT CCGAGC-3 0 ) and forward primer 4P (5 0 -TCGGATCCCC GGGGAAACCTGGAGCG-3 0 ) (Behjatnia et al 1996) and (2) RT and reverse primer 2A (5 0 -TGTTTCCACCGGTAG TAGC-3 0 ) and forward primer 1S (5 0 -ACTCGTGGTTCC TGTGGTTC-3 0 ) (Herold et al 1992). RT was done by the direct microtissue sampling method, using a syringe needle (25 G 9 25 mm; Terumo, Tokyo, Japan) to pierce the leaf or stem tissue of diseased tomatoes to a depth of 0.1-0.2 mm, as previously described by Hosokawa et al (2006).…”