Journal de pathologie végétale et de microbiologie

Abstrait

Replication of Avocado Sunblotch Viroid in the Cyanobacterium Nostoc Sp. PCC 7120

Amel Latifi, Christophe Bernard, Laura da Silva, Yannick Andéol, Amine Elleuch, Véronique Risoul, Jacques Vergne and Marie-Christine Maurel

Viroids are small infectious RNA molecules that replicate in plants via RNA-RNA replication processes. The molecular mechanism responsible for this replication has attracted great interest, and studies on this topic have yielded interesting biological findings on the processes in which RNA is involved. Viroids belonging to the Avsunviroidae family replicate in the chloroplasts of infected hosts. It has by now been established that chloroplasts and cyanobacteria share a common have ancestor. In view of this phylogenetic relationship, we investigated whether a member of the Avsunviroidae family could be replicated in a cyanobacterium. The results obtained here show that Avocado Sunblotch Viroid (ASBVd) RNA is able to replicate in the filamentous cyanobacterium Nostoc PCC 7120. Indeed, Northern blot hybridization showed that linear forms of “minus” polarity were detected in RNA extracted from Nostoc cells expressing ASBVd dimers of positive “polarity”, and that linear forms of “negative” polarity were detected in RNA extracted from Nostoc cells expressing ASBVd dimers of “positive” polarity. ASBVd replication does not impair the growth of Nostoc. These results provide the first evidence that a prokaryotic cell possesses all the machinery required to sustain the process of RNA-RNA replication. The data obtained here are of great importance, since they might shed light on the evolution of the cellular factors on which RNA replication processes depend.