title: Dual involvement of a Medicago truncatula NAC transcription factor in root abiotic stress response and symbiotic nodule senescence.
abstract: Legume crops related to the model plant Medicago truncatula can adapt their root architecture to environmental conditions, both by branching and by establishing a symbiosis with rhizobial bacteria to form nitrogen-fixing nodules. Soil salinity is a major abiotic stress affecting plant yield and root growth. Previous transcriptomic analyses identified several transcription factors linked to the M. truncatula response to salt stress in roots, including NAC (NAM/ATAF/CUC)-encoding genes. Over-expression of one of these transcription factors, MtNAC969, induced formation of a shorter and less-branched root system, whereas RNAi-mediated MtNAC969 inactivation promoted lateral root formation. The altered root system of over-expressing plants was able to maintain its growth under high salinity, and roots in which MtNAC969 was down-regulated showed improved growth under salt stress. Accordingly, expression of salt stress markers was decreased or induced in MtNAC969 over-expressing or RNAi roots, respectively, suggesting a repressive function for this transcription factor in the salt-stress response. Expression of MtNAC969 in central symbiotic nodule tissues was induced by nitrate treatment, and antagonistically affected by salt in roots and nodules, similarly to senescence markers. MtNAC969 RNAi nodules accumulated amyloplasts in the nitrogen-fixing zone, and were prematurely senescent. Therefore, the MtNAC969 transcription factor, which is differentially affected by environmental cues in root and nodules, participates in several pathways controlling adaptation of the M. truncatula root system to the environment.
authors.affiliation: Institut des Sciences du Végétal (ISV), Centre National de la Recherche Scientifique, 91198 Gif sur Yvette Cedex, France.
authors.forename: Axel
authors.initials: A
authors.lastname: de Zélicourt
authors.forename: Anouck
authors.initials: A
authors.lastname: Diet
authors.forename: Jessica
authors.initials: J
authors.lastname: Marion
authors.forename: Carole
authors.initials: C
authors.lastname: Laffont
authors.forename: Federico
authors.initials: F
authors.lastname: Ariel
authors.forename: Michaël
authors.initials: M
authors.lastname: Moison
authors.forename: Ons
authors.initials: O
authors.lastname: Zahaf
authors.forename: Martin
authors.initials: M
authors.lastname: Crespi
authors.forename: Véronique
authors.initials: V
authors.lastname: Gruber
authors.forename: Florian
authors.initials: F
authors.lastname: Frugier
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D054884:Host-Pathogen Interactions; D017403:In Situ Hybridization; D046913:Medicago truncatula / Q000235:genetics* / Q000254:growth & development / Q000382:microbiology; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics* / Q000254:growth & development / Q000382:microbiology; D030821:Plants, Genetically Modified; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053204:Root Nodules, Plant / Q000235:genetics* / Q000382:microbiology / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid; D016962:Sinorhizobium meliloti / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological; D013559:Symbiosis; D014157:Transcription Factors / Q000145:classification / Q000235:genetics* / Q000378:metabolism
chemical_list: D010937:Plant Growth Regulators; D010940:Plant Proteins; D014157:Transcription Factors; D012965:Sodium Chloride