Processing precursors with RNase III in plants

RNase III endonucleases cleave double-stranded RNA to produce different classes of mature RNAs that participate in pre-mRNA splicing, RNA modification, translation, gene silencing, ribosomal biogenesis, and regulation of developmental timing. The approximately 120-amino acid long endonuclease domain (endoND) is the hallmark of this family of proteins, generally recognized by a nine amino acid signature within the domain. The endoND module occurs in a single or double copy in different classes of proteins, alone or with other domains that provide versatility to act in different situations requiring RNA processing. Two groups of proteins containing the endoribonuclease domain can be described in plants. One group represents the RNase III-like enzymes called Dicer-like (DCL) that generate small RNA molecules of specific lengths from longer precursors. There are four classes of DCL enzymes each class producing predominantly one particular processing product. The other group includes non-dicer-like enzymes (non-DCL) with various types of recently described enzymes most of which have not been functionally characterized. Non-DCL comprise the RNase III-like enzymes (RTL1, 2 and 3) identified in Arabidopsis thaliana, the RNC1 RNase III enzyme isolated from maize and the in silico predicted Mini-RNase III that consists only of an endonuclease domain. RTLs and RNC1 participate in development, splicing, and responses to biotic stress. Mini-RNase III enzymes await functional characterization in plants.