microRNA involvement in root organ formation and function in Medicago truncatula

Abstract

Plant root architecture is regulated by the formation and function of meristems at the sites of root organogenesis. Meristem formation requires the generation of stem cell niches which produce the new cells of the growing organ. microRNAs (miRNAs) have emerged as regulators of many key biological functions in plants including root organogenesis. To identify key miRNAs involved in root meristem formation in M. truncatula, deep sequencing was used to compare the miRNA populations between root tip (RT), containing root apical meristem, and elongation zone (EZ) tissue plus root forming callus (RFC) and non-root forming callus (NRFC). We identified 83 previously reported miRNAs, 24 new to M. truncatula, in 44 families. Functional analysis was performed on two of these predicted miRNAs, miRN304 and miR166g-5p. Over-expression of novel miRNA, miRN304, produces severe root abnormalities including stunted growth, loss of meristem structure and a poorly formed vasculature. mtr-miR166a-5p corresponds to the passenger strand of miR166a-3p, a miRNA previously shown to negatively regulate lateral root and nodule numbers. miR166a-5p over-expression results in increased nodule numbers and acts independently of miR166a-3p and may be a previously un-identified. Show more