Peach latent mosaic viroid variants inducing peach calico (extreme chlorosis) contain a characteristic insertion that is responsible for this symptomatology

Abstract

The involvement of Peach latent mosaic viroid (PLMVd) in an extensive chlorosis of peach known as calico (PC) has been advanced but ultimate proof is lacking. Sequencing of 16 full-length PLMVd cDNA clones of a PC isolate revealed two groups of variants. Nine had a size (336-338 nt) similar to that of typical PLMVd variants of nonsymptomatic and mosaic-inducing isolates, whereas the other 7 were longer (348-351 nt) due to an insertion of 12-13 nt. This insertion was always found in the hairpin loop capping the hammerhead arm, had a limited sequence variability, and folded itself into a hairpin. When three PLMVd dimeric transcripts, two with and the other without the insertion, were slash-inoculated on GF-305 peach seedlings, PC symptoms were produced exclusively by the RNAs containing the insertion, which was conserved in the progeny. These data demonstrate that the agent of PC is PLMVd. Direct support that the 12- to 13-nt insertion contains the PC pathogenicity determinant was obtained by its removal through site-directed mutagenesis from one of the PC-inducing variants. Inoculations with dimeric transcripts of the resulting variant showed that it could replicate but without eliciting symptoms. Our results also suggest that the insertion emerges sporadically de novo.

Low incidence of peach latent mosaic viroid in peach mother blocks in Serbia

“…PLMVd, usually a 335-339-long nucleotide (nt), is a typical species of the genus Pelamoviroid (family Avsunviroidae). Cloning and sequencing of PLMVd variants of asymptomatic and mosaic-inducing peach isolates have revealed a wide range of variants with sizes between 335 and 351 nt (Pelchat et al, 2000;Malfitano et al, 2003). PLMVd does not have a central conserved region (CCR) and has acquired selfcleaving properties by forming hammerhead ribozyme structures (Flores & Llácer, 1989).…”

Estudios de Patogenicidad de Viroides del Género Apscaviroide y Hostuviroide en cítricos.

“…Se han descrito infecciones viroidales en plantas herbáceas y leñosas así como en plantas dicotiledóneas y monocotiledóneas. (Reanwarakorn y Semancik, 1998;Malfitano et al 2003).…”

“…Most studies on viroid pathogenesis have been undertaken with PSTVd, the type species of the family Pospiviroidae, or with Peach latent mosaic viroid (Malfitano et al, 2003) and Chrysanthemum chlorotic viroid (De la as representative members of the family Avsunviroidae. In PSTVd, sequence variations related to symptom severity have been essentially mapped to the P domain (Schnölzer et al, 1985;Owens et al, 1991Owens et al, , 1995Owens et al, , 1996, but more recent reports have shown that the left and right terminal domains, as well as a single substitution in the loop E within the C domain, also contribute to symptom expression .…”

Respuesta De Distintos Genotipos De Cítricos Y Géneros Afines a La Infección Con Viroides

“…Estudios paralelos con miembros de la familia Avsunviroidae han revelado distorsiones en cloroplastos y presencia de cuerpos membranosos en las regiones cloróticas de hojas infectadas con el ASBVd, mientras que en hojas totalmente cloróticas se observan lo que parecen ser proplastidios alterados en vez de cloroplastos (Desjardins, 1987). Esta última observación ha sido reproducida en hojas infectadas con el PLMVd, algunas de cuyas variantes inducen una clorosis extrema (cálico), que en los casos más agudos cubre toda la superficie foliar (Malfitano et al, 2003;Rodio et al, 2006 Rodio et al, y 2007.…”

“…Estudios paralelos con miembros de la familia Avsunviroidae han revelado distorsiones en cloroplastos y presencia de cuerpos membranosos en las regiones cloróticas de hojas infectadas con el ASBVd, mientras que en hojas totalmente cloróticas se observan lo que parecen ser proplastidios alterados en vez de cloroplastos (Desjardins, 1987). Esta última observación ha sido reproducida en hojas infectadas con el PLMVd, algunas de cuyas variantes inducen una clorosis extrema (cálico), que en los casos más agudos cubre toda la superficie foliar (Malfitano et al, 2003;Rodio et al, 2006 Rodio et al, y 2007.También existen importantes diferencias en cuanto a la gama de huéspedes. Un caso extremo lo constituyen los viroides de la familia Avsunviroidae cuyo espectro se restringe a una sola o a un grupo reducido de especies próximas, mientras que otros viroides como el HSVd colonizan multitud de especies distintas, produciendo tanto enfermedades como infecciones latentes (Shikata, 1990;.…”