A Viroid RNA with a Specific Structural Motif Inhibits Chloroplast Development

Abstract

Peach latent mosaic viroid (PLMVd) is a chloroplast-replicating RNA that propagates in its natural host, peach (Prunus persica), as a complex mixture of variants, some of which are endowed with specific structural and pathogenic properties. This is the case of variant PC-C40, with an insertion of 12 to 13 nucleotides that folds into a hairpin capped by a U-rich loop, which is responsible for an albino-variegated phenotype known as peach calico (PC). We have applied a combination of ultrastructural, biochemical, and molecular approaches to dissect the pathogenic effects of PC-C40. Albino sectors of leaves infected with variant PC-C40 presented palisade cells that did not completely differentiate into a columnar layer and altered plastids with irregular shape and size and with rudimentary thylakoids, resembling proplastids. Furthermore, impaired processing and accumulation of plastid rRNAs and, consequently, of the plastid translation machinery was observed in the albino sectors of leaves infected with variant PC-C40 but not in the adjacent green areas or in leaves infected by mosaic-inducing or latent variants (including PC-C40D, in which the 12-to 13-nucleotide insertion was deleted). Protein gel blot and RT-PCR analyses showed that the altered plastids support the import of nucleus-encoded proteins, including a chloroplast RNA polymerase, the transcripts of which were detected. RNA gel blot and in situ hybridizations revealed that PLMVd replicates in the albino leaf sectors and that it can invade the shoot apical meristem and induce alterations in proplastids, bypassing the RNA surveillance system that restricts the entry of a nucleus-replicating viroid and most RNA viruses. Therefore, a non-protein-coding RNA with a specific structural motif can interfere with an early step of the chloroplast developmental program, leading ultimately to an albino-variegated phenotype resembling that of certain variegated mutants in which plastid rRNA maturation is also impaired. Our results highlight the potential of viroids for further dissection of RNA trafficking and pathogenesis in plants.

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

“…Data supporting this notion include the effects of tagetitoxin, which inhibits PEP but not NEP, on in vitro synthesis of host and viroid RNAs by chloroplastic preparations from ASBVd-infected tissue, 47 together with active PLMVd replication in peach leaves showing a PLMVd-induced albinism wherein PEP-dependent transcription is essentially abolished. 48 Other data, however, have proposed the involvement of PEP in PLMVd replication, although they have been obtained with a heterologous in vitro system (replacing PEP by the RNA polymerase of Escherichia coli).…”

Inducible transgenic tobacco system to study the mechanisms underlying chlorosis mediated by the silencing of chloroplast heat shock protein 90

“…An earlier study suggested that PLMVd replicates in the chloroplast, blocks the chloroplast development, and leads to the depletion of chloroplastencoded proteins [21]. The PLMVd variants associated with PC contain an insertion of 12-14 nt that folds into a hairpin with a U-rich tetraloop, the sequence of which is critical for inciting the albino phenotype.…”

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

“…El sistema vascular en sus proximidades aún no está diferenciado por lo que su acceso solo puede darse por movimientos célula a célula. Mediante hibridación in situ se ha comprobado que el PSTVd queda excluido de los ápices meristemáticos de plantas infectadas de tomate y Nicotiana benthamiana (Zhu et al, 2001), mientras que el PLMVd sí que parece invadir células muy cercanas a dichos ápices meristemáticos de plantas de melocotonero infectadas (Rodio et al, 2007). Estas observaciones sugieren que existen distintos mecanismos que rigen esta clase de movimiento en los miembros de las familias Pospiviroidae y Avsunviroidae.…”