Biology and Function of miR159 in Plants.

MicroR159 (miR159) is ancient, being present in the majority of land plants where it targets a class of regulatory genes called or via highly conserved miR159-binding sites. These genes encode R2R3 MYB domain transcription factors that transduce the gibberellin (GA) signal in the seed aleurone and the anther tapetum. Here, plays a conserved role in promoting the programmed cell death of these tissues, where miR159 function appears weak. By contrast, is not involved in GA-signaling in vegetative tissues, but rather its expression is deleterious, leading to the inhibition of growth and development. Here, the major function of miR159 is to mediate strong silencing of to enable normal growth. Highlighting this requirement of strong silencing are conserved RNA secondary structures associated with the miR159-binding site in mRNA that promotes miR159-mediated repression. Although the miR159- pathway in vegetative tissues has been implicated in a number of different functions, presently no conserved role for this pathway has emerged. We will review the current knowledge of the different proposed functions of miR159, and how this ancient pathway has been used as a model to help form our understanding of miRNA biology in plants.