PTGS Has Ancient Roots
Discoveries from both genetic and biochemical approaches point to the fact that PTGS has deep evolutionary roots. Proposals have been put forth that PTGS evolved as a defense mechanism against transposons or RNA viruses, perhaps before plants and animals diverged (1, 3, 17, 18).
Interestingly, it was noted by many researchers that disruption of genes required for RNAi often causes severe developmental defects. This observation suggested a link between RNAi and at least one developmental pathway.
A group of small RNA molecules, known as small temporal
RNAs (stRNAs), regulates C. elegans developmental timing through
translational repression of target transcripts. Research indicates that
the C. elegans lin-4 and let-7 stRNAs are generated
from 70-nt transcripts following the folding of these longer tran