Identification and expression analysis of a microRNA cluster derived from pre-ribosomal RNA in Papaver somniferum L. and Papaver bracteatum L.

Opium poppy (Papaver somniferum L.) is one of the ancient medical crops, which produces several important alkaloids such as morphine, noscapine, sanguinarine and codeine. MicroRNAs are endogenous non-coding RNAs that play important regulatory roles in plant diverse biological processes.