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

Abstract

Citrus exocortis viroid (CEVd) is the causal agent of exocortis disease of citrus. CEVd has a wide host range that includes woody and herbaceous species. A new CEVd strain (CEVd(COL)), phylogenetically clustering with CEVd variants of Class A inducing severe symptoms in tomato, was identified in Colombia and shown to induce only extremely mild symptoms in Etrog citron indicator plants. Using site-directed mutagenesis, two nucleotide substitutions (314A → G and 315U → A) in the lower strand of the P domain of the predicted CEVd(COL) secondary structure resulted in a severe artificial CEVd(MCOL) variant. Conversely, two nucleotide exchanges (314G → A and 315A → U) in the same region of the severe variant CEVd(E-117) resulted in a symptomless artificial CEVd(ME-117) variant. Infectivity assays conducted with the natural and mutated variants showed that all induced severe symptoms in Gynura aurantiaca, tomato and chrysanthemum. This is the first report of the identification of pathogenic determinants of CEVd in citrus, and shows that these pathogenicity determinants are host dependent.

Construction of Infectious cDNA Clone of a Chrysanthemum stunt viroid Korean Isolate

“…Our sequence analyses of the CSVd-SK1 isolated from two host species suggest that the CSVd isolates are likely to change some nucleotides in their genomes when the CSVd isolates replicate, depending on the host species ( Gross et al, 1982 ; Matsushita and Penmetcha, 2009 ). We could not exclude completely the possibility that consecutive passages of CSVd from the cDNA clones of CSVd-SK1 give rise to substitutions, deletions, and insertions in the genome of CSVd in natural host species, such as chrysanthemum, tomato, petunia, pepper and potato ( Murcia et al, 2011 ). Whether a series of passages for CSVd in specific host species affects infectivity by sequence variations remains to be determined.…”

The use of a combination of computer‐assisted structure prediction and SHAPE probing to elucidate the secondary structures of five viroids

“…It corresponds to loops 8 and 9 of PSTVd, which have been suggested to impair trafficking when mutated following the infection of Nicotiana benthamiana plants (Zhong et al ., 2008). Other reports have claimed that the mutation of this region affects the infection mechanisms of both PSTVd (Wiesyk et al ., 2011) and CEVd (Murcia et al ., 2011; Visvader and Symons, 1986).…”

Microarray analysis of Etrog citron (Citrus medica L.) reveals changes in chloroplast, cell wall, peroxidase and symporter activities in response to viroid infection

“…In spite of the existence of many symptomless hosts, the questions of why and how viroids induce disease symptoms in certain hosts remain far from understood. Studies aimed at the identification of segment(s) of the viroid molecule associated with symptom modulation have provided relevant information, indicating that the pathogenicity and variable domains of the rod‐like secondary structure play a key role as molecular determinants of pathogenicity in members of the family Pospiviroidae (Chaffai et al ., 2007; Góra et al ., 1996; Murcia et al ., 2011; Reanwarakorn and Semancik, 1998; Serra et al ., 2008; Visvader and Symons, 1986). In some members of the Avsunviroidae family with branched secondary structures, the pathogenicity determinants have been mapped in a U‐rich tetraloop (De la Peña et al ., 1999; Malfitano et al ., 2003).…”