Referencia

Proc Natl Acad Sci USA 2012; 109 (34): 13805-13810. doi: 10.1073/pnas.1206187109.

Autores

María-Ángeles Nohales, Ricardo Flores y José-Antonio Daròs

Resumen

Viroids are a unique class of noncoding RNAs: composed of only a circular, single-stranded molecule of 246-401 nt, they manage to replicate, move, circumvent host defenses, and frequently induce disease in higher plants. Viroids replicate through an RNA-to-RNA rolling-circle mechanism consisting of transcription of oligomeric viroid RNA intermediates, cleavage to unit-length strands, and circularization. Though the host RNA polymerase II (redirected to accept RNA templates) mediates RNA synthesis and a type-III RNase presumably cleavage of Potato spindle tuber viroid (PSTVd) and closely related members of the family Pospiviroidae, the host enzyme catalyzing the final circularization step, has remained elusive. In this study we propose that PSTVd subverts host DNA ligase 1, converting it to an RNA ligase, for the final step. To support this hypothesis, we show that the tomato (Solanum lycopersicum L.) DNA ligase 1 specifically and efficiently catalyzes circularization of the genuine PSTVd monomeric linear replication intermediate opened at position G95-G96 and containing 5′-phosphomonoester and 3′-hydroxyl terminal groups. Moreover, we also show a decreased PSTVd accumulation and a reduced ratio of monomeric circular to total monomeric PSTVd forms in Nicotiana benthamiana Domin plants in which the endogenous DNA ligase 1 was silenced. Thus, in a remarkable example of parasitic strategy, viroids reprogram for their replication the template and substrate specificity of a DNA-dependent RNA polymerase and a DNA ligase to act as RNA-dependent RNA polymerase and RNA ligase, respectively.

Descripción

Los viroides son pequeños RNAs circulares no codificantes que infectan plantas. Se replican a través de un mecanismo de círculo rodante con intermediarios de RNA que consta de la síntesis de RNAs viroidales oligoméricos, su corte a monómeros y la circularización de estos últimos. Este estudio muestra como el viroide del tubérculo fusiforme de la patata (PSTVd) es capaz de subvertir la actividad de la DNA ligasa 1 de su huésped (tomate), convirtiéndola en una RNA ligasa, para que catalice su circularización durante el paso final de su replicación.

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REFERENCIA DEL GRUPO INVESTIGADOR

El grupo de “Biotecnología de Virus de Plantas” que dirige el Dr. José Antonio Darós Arnau en el Instituto de Biología Molecular y Celular de Plantas (CSIC-Universidad Politécnica de Valencia) investiga la interacción que se produce entre las plantas y algunos de sus patógenos virales y subvirales. Con el estudio de esta interacción se pretende entender algunos aspectos básicos del funcionamiento de las biomoléculas, así como desarrollar herramientas biotecnológicas para la protección, mejora e innovación en los cultivos.

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