Extremely High Mutation Rate of a Hammerhead Viroid
Selma Gago,1
Santiago F. Elena,1
Ricardo Flores,1
Rafael Sanjuán1,2*
The mutation rates of viroids, plant pathogens with minimal
non-protein-coding RNA genomes, are unknown. Their replication
is mediated by host RNA polymerases and, in some cases, by hammerhead
ribozymes, small self-cleaving motifs embedded in the viroid.
By using the principle that the population frequency of nonviable
genotypes equals the mutation rate, we screened for changes
that inactivated the hammerheads of
Chrysanthemum chlorotic mottle viroid. We obtained a mutation rate of 1/400 per site,
the highest reported for any biological entity. Such error-prone
replication can only be tolerated by extremely simple genomes
such as those of viroids and, presumably, the primitive replicons
of the RNA world. Our results suggest that the emergence of
replication fidelity was critical for the evolution of complexity
in the early history of life.
2 Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, 46980 València, Spain.
* To whom correspondence should be addressed. E-mail: rafael.sanjuan{at}uv.es
