Isolation and cloning of small RNAs from virus-infected plants.

RNA silencing is an evolutionarily conserved, RNA-mediated, regulatory system of eukaryotic organisms that also acts as an antiviral system in plants and animals. A defining feature of RNA silencing is the presence of 21- to 26-nucleotide small RNAs corresponding to the silencing target sequence, which in virus-infected plants are derived from the viral genome. The virus-derived small RNAs have a nonrandom distribution along the viral genome, suggesting hotspots for viral small-RNA generation. The isolated small RNAs can be used either as probes for hybridization studies or for directional cloning in order to get detailed information about their sizes, origins, and functions. This unit describes an isotope-free small-RNA cloning procedure that utilizes unmodified small RNAs and is routinely used to characterize small RNAs from various plant tissues.