Methods for isolation of total RNA to recover miRNAs and other small RNAs from diverse species.

For the experimental analysis of miRNAs and other small RNAs in the 20–25 nucleotide (nt) size range, the first and most important step is the isolation of high-quality total RNA. Because RNA degradation products can mask or dilute the presence of true miRNAs, it is important when choosing a method that it efficiently extracts RNA from tissues in a manner that prevents degradation of RNA of both high and low molecular weight. In addition, the presence of polyphenols, polysaccharides, and secondary metabolites may render nucleic acids insoluble, and hinder the recovery of the miRNAs. Finally, and most importantly, the method chosen must be capable of retaining the small RNA component. In this chapter, we will present a set of total RNA isolation methods that can be used to maximize the recovery of high-quality RNA to be used in miRNA analysis for a large number of plant species and tissue types.