An artificial chimeric derivative of Citrus viroid V involves the terminal left domain in pathogenicity

Abstract

The recently described Citrus viroid V (CVd-V) induces, in Etrog citron, mild stunting and very small necrotic lesions and cracks, sometimes filled with gum. As Etrog citron plants co-infected with Citrus dwarfing viroid (CDVd) and CVd-V show synergistic interactions, these host-viroid combinations provide a convenient model to identify the pathogenicity determinant(s). The biological effects of replacing limited portions of the rod-like structure of CVd-V with the corresponding portions of CDVd are reported. Chimeric constructs were synthesized using a novel polymerase chain reaction-based approach, much more flexible than those based on restriction enzymes used in previous studies. Of the seven chimeras (Ch) tested, only one (Ch5) proved to be infectious. Plants infected with Ch5 showed no symptoms and, although this novel chimera was able to replicate to relatively high titres in singly infected plants, it was rapidly displaced by either CVd-V or CDVd in doubly infected plants. The results demonstrate that direct interaction(s) between structural elements in the viroid RNA (in this case, the terminal left domain) and as yet unidentified host factors play an important role in modulating viroid pathogenicity. This is the first pathogenic determinant mapped in species of the genus Apscaviroid.

Identification of the experimental herbaceous host range of the Apscaviroids infecting citrus species

“…Earlier attempts failed to transfer CVd-V or its artificial chimers to herbaceous plants (Serra et al, 2009). However, evidence of de novo replication of Australian grapevine viroid and apple scar skin viroid (type member of the Apscaviroid) in several herbaceous plants have been reported (Rezaian, 1990;Zakiaghl and Izadpanah, 2010;Walia et al, 2014).…”

Two nucleotide positions in the Citrus exocortis viroid RNA associated with symptom expression in Etrog citron but not in experimental herbaceous hosts

“…The results reported here on the modulation of symptom expression in CEVd‐infected Etrog citron plants show the same trend as those described for PSTVd. It was also observed that CEVd COL ‐infected plants displayed extremely subtle leaf distortion, suggesting that other positions of the viroid molecule may also play a role in the modulation of symptom expression, as already reported for the T L , T R and C domains of PSTVd (Qi and Ding, 2003; Sano et al ., 1992) and for the T L domain of Citrus viroid V (CVd‐V) and Citrus dwarfing viroid (CDVd), two members of the genus Apscaviroid (Murcia et al ., 2009a; Serra et al ., 2009).…”