On the complexity of miRNA-mediated regulation in plants: novel insights into the genomic organization of plant miRNAs.

MicroRNAs (miRNAs) are endogenous small non-coding RNAs of about 20-24 nt, known to play key roles in post-transcriptional gene regulation, that can be coded either by intergenic or intragenic loci. Intragenic (exonic and intronic) miRNAs can exert a role in the transcriptional regulation and RNA processing of their host gene. Moreover, the possibility that the biogenesis of exonic miRNAs could destabilize the corresponding protein-coding transcript and reduce protein synthesis makes their characterization very intriguing and suggests a possible novel mechanism of post-transcriptional regulation of gene expression. This work was designed to carry out the computational identification of putative exonic miRNAs in 30 plant species and the analysis of possible mechanisms involved in their regulation. The results obtained represent a useful starting point for future studies on the complex networks involved in microRNA-mediated gene regulation in plants.