This invention relates to isolated nucleic acid fragments encoding polypeptides involved in post-transcriptional gene silencing. The invention also relates to construction of a recombinant DNA construct encoding all or a portion of the polypeptide involved in post-transcriptional gene silencing, in sense or antisense orientation, wherein expression of the recombinant DNA construct results in production of altered levels in a transformed host cell of the the polypeptide involved in post-transcriptional gene silencing.