Rice embryogenic calli express a unique set of microRNAs, suggesting regulatory roles of microRNAs in plant post-embryogenic development

In vitro cultured embryogenic callus was employed as a model to investigate microRNAs (miRNAs) associated with embryogenesis and post-embryonic development. Thirty-one miRNAs including 16 novel species were identified from a large number of small RNAs which were cloned from both differentiated and undifferentiated rice embryogenic calli. Four target genes of the miRNAs were further validated. A set of the miRNAs, including miR397 and miR156, exhibited intriguing expression patterns during the transition from undifferentiated to differentiated calli. By exploiting the correlations between the differential expression patterns of these miRNAs and their targets, the regulatory roles of the miRNAs on meristem maintenance and embryogenesis were indicated.