Tissue and intra‐cellular distribution of coconut cadang cadang viroid and citrus exocortis viroid determined by in situ hybridization and confocal laser scanning and transmission electron microscopy

Abstract

Confocal laser scanning microscopy and transmission electron microscopy (TEM) were used in conjunction with in situ hybridization techniques to compare and contrast the subnuclear (ultrastructural) and tissue (histological) localizations, respectively, of citrus exocortis viroid (CEV) and coconut cadang cadang viroid (CCCV). Both these viroids, which are members of the same taxonomic subgroup of viroids, were found in the vascular tissues as well as in the nuclei of mesophyll cells of infected host plants. At the subnuclear level, however, CEV was distributed across the entire nucleus, in contrast to CCCV which was mostly concentrated in the nucleolus with the remainder distributed throughout the nucleoplasm.

Rolling-circle replication of viroids, viroid-like satellite RNAs and hepatitis delta virus: Variations on a theme

“…Early studies detected the most abundant PSTVd circular RNA-arbitrarily regarded as having (+) polarity-and its oligomeric (-) strands in nuclear fractions, strongly implicating a nuclear RNA polymerase in replication. 8,12 Employing finer tools, these results were confirmed for PSTVd and extended to other members of the family Pospiviroidae, 30,31 which are usually referred to as nuclear viroids. Remarkably, similar experiments showed the preferential accumulation in plastids of (+) and (-) strands of ASBVd and other members of the family Avsunviroidae, which are usually referred to as chloroplastic viroids and assumed to be replicated by a chloroplastic RNA polymerase.…”

A Viroid RNA with a Specific Structural Motif Inhibits Chloroplast Development

“…Viroids are grouped into two taxonomic families on the basis of their biological, structural, and biochemical properties (Flores et al, 2005b). Members of the family Pospiviroidae, type species Potato spindle tuber viroid (PSTVd) (Diener, 1972;Gross et al, 1978), adopt a rod-like or quasi-rod-like conformation with characteristic motifs, prominent among them a central conserved region, and replicate in the nucleus by an asymmetric rolling-circle mechanism (Branch et al, 1988;Harders et al, 1989;Bonfiglioli et al, 1996;Qi and Ding, 2003b). By contrast, members belonging to the family Avsunviroidae Fadda et al, 2003), type species Avocado sunblotch viroid (ASBVd) (Symons, 1981;Hutchins et al, 1986), may adopt branched conformations, do not contain a central conserved region, and replicate in the chloroplast by a symmetric rollingcircle mechanism in which the oligomeric strands of both polarities self-cleave through hammerhead ribozymes (Bonfiglioli et al, 1994;Darò s et al, 1994;Lima et al, 1994;Bussiè re et al, 1999;Navarro et al, 1999).…”

Differential Subnuclear Localization of RNA Strands of Opposite Polarity Derived from an Autonomously Replicating Viroid[W]

“…The subcellular localization of two other members of the Pospiviroidae also has been investigated. In tissue sections of infected plants, in situ hybridization revealed that Citrus exocortis viroid (CEVd) was localized throughout the nucleus, whereas Coconut cadang cadang viroid was distributed mostly in the nucleolus and to a lesser extent in the nucleoplasm (Bonfiglioli et al, 1996). Both the ( ϩ )-and ( Ϫ )-RNAs of these viroids exhibited similar distribution patterns, although the hybridization signal for the ( Ϫ )-RNA was much weaker (Bonfiglioli et al, 1996).…”

“…In tissue sections of infected plants, in situ hybridization revealed that Citrus exocortis viroid (CEVd) was localized throughout the nucleus, whereas Coconut cadang cadang viroid was distributed mostly in the nucleolus and to a lesser extent in the nucleoplasm (Bonfiglioli et al, 1996). Both the ( ϩ )-and ( Ϫ )-RNAs of these viroids exhibited similar distribution patterns, although the hybridization signal for the ( Ϫ )-RNA was much weaker (Bonfiglioli et al, 1996). These data invoked speculation about whether the nucleolus-localized DNA-dependent RNA polymerase I was involved in some aspects of replication in addition to the possible nucleolar import of the ( Ϫ )-and ( ϩ )-strand RNAs (Bonfiglioli et al, 1996).…”