title: MicroRNA166 controls root and nodule development in Medicago truncatula.
abstract: Legume root architecture is characterized by the development of two de novo meristems, leading to the formation of lateral roots or symbiotic nitrogen-fixing nodules. Organogenesis involves networks of transcription factors, the encoding mRNAs of which are frequently targets of microRNA (miRNA) regulation. Most plant miRNAs, in contrast with animal miRNAs, are encoded as single entities in an miRNA precursor. In the model legume Medicago truncatula, we have identified the MtMIR166a precursor containing tandem copies of MIR166 in a single transcriptional unit. These miRNAs post-transcriptionally regulate a new family of transcription factors associated with nodule development, the class-III homeodomain-leucine zipper (HD-ZIP III) genes. In situ expression analysis revealed that these target genes are spatially co-expressed with MIR166 in vascular bundles, and in apical regions of roots and nodules. Overexpression of the tandem miRNA precursor correlated with MIR166 accumulation and the downregulation of several class-III HD-ZIP genes, indicating its functionality. MIR166 overexpression reduced the number of symbiotic nodules and lateral roots, and induced ectopic development of vascular bundles in these transgenic roots. Hence, plant polycistronic miRNA precursors, although rare, can be processed, and MIR166-mediated post-transcriptional regulation is a new regulatory pathway involved in the regulation of legume root architecture.
authors.affiliation: Institut des Sciences du Végétal (ISV), Centre National de la Recherche Scientifique (CNRS), 91198 Gif sur Yvette Cedex, France.
authors.forename: Adnane
authors.initials: A
authors.lastname: Boualem
authors.forename: Philippe
authors.initials: P
authors.lastname: Laporte
authors.forename: Mariana
authors.initials: M
authors.lastname: Jovanovic
authors.forename: Carole
authors.initials: C
authors.lastname: Laffont
authors.forename: Julie
authors.initials: J
authors.lastname: Plet
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Combier
authors.forename: Andreas
authors.initials: A
authors.lastname: Niebel
authors.forename: Martin
authors.initials: M
authors.lastname: Crespi
authors.forename: Florian
authors.initials: F
authors.lastname: Frugier
mesh_terms: D001483:Base Sequence; D015152:Blotting, Northern; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D017403:In Situ Hybridization; D046913:Medicago truncatula / Q000254:growth & development*; D035683:MicroRNAs / Q000235:genetics / Q000502:physiology*; D018517:Plant Roots / Q000254:growth & development*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D035683:MicroRNAs