Identification of novel microRNAs in rice (Oryza sativa) based on the cleavage signals in precursors

MicroRNAs (miRNAs) are crucial regulators of gene expression in plants and a growing number of novel miRNA genes have been cloned in rice in recent years. However, there is no evidence that all miRNAs have been discovered, especially for those low expression ones which are difficult to be found by conventional methods. By taking advantage of the finding that DCL1-mediated cleavage signals for the processing of the miRNA precursors could be used as the clues for novel miRNAs’ discovery, a genome-wide search for rice miRNA candidates was carried out. As a result, 51 previously validated miRNAs and 24 novel miRNA candidates were discovered. After target prediction and degradome sequencing data-based validation, coupled with reverse approach retest, 10 miRNA candidate–mRNA target pairs were further identified, providing a basis for in-depth functional analysis of these miRNA candidates. Besides, some isomiRs found in this study showed more likely to be the real miRNAs. We also found an exceptional example which did not obey the rule that 22-nt miRNAs have the ability to trigger the phased siRNAs production from the cleaved targets.