title: A Transcriptional Program for Arbuscule Degeneration during AM Symbiosis Is Regulated by MYB1.
abstract: During the endosymbiosis formed between plants and arbuscular mycorrhizal (AM) fungi, the root cortical cells are colonized by branched hyphae called arbuscules, which function in nutrient exchange with the plant [1]. Despite their positive function, arbuscules are ephemeral structures, and their development is followed by a degeneration phase, in which the arbuscule and surrounding periarbuscular membrane and matrix gradually disappear from the root cell [2, 3]. Currently, the root cell's role in this process and the underlying regulatory mechanisms are unknown. Here, by using a Medicago truncatula pt4 mutant in which arbuscules degenerate prematurely [4], we identified arbuscule degeneration-associated genes, of which 38% are predicted to encode secreted hydrolases, suggesting a role in disassembly of the arbuscule and interface. Through RNAi and analysis of an insertion mutant, we identified a symbiosis-specific MYB-like transcription factor (MYB1) that suppresses arbuscule degeneration in mtpt4. In myb1, expression of several degeneration-associated genes is reduced. Conversely, in roots constitutively overexpressing MYB1, expression of degeneration-associated genes is increased and subsequent development of symbiosis is impaired. MYB1-regulated gene expression is enhanced by DELLA proteins and is dependent on NSP1 [5], but not NSP2 [6]. Furthermore, MYB1 interacts with DELLA and NSP1. Our data identify a transcriptional program for arbuscule degeneration and reveal that its regulators include MYB1 in association with two transcriptional regulators, NSP1 and DELLA, both of which function in preceding phases of the symbiosis. We propose that the combinatorial use of transcription factors enables the sequential expression of transcriptional programs for arbuscule development and degeneration.
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Daniela S
authors.initials: DS
authors.lastname: Floss
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: S Karen
authors.initials: SK
authors.lastname: Gomez
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Hee-Jin
authors.initials: HJ
authors.lastname: Park
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Allyson M
authors.initials: AM
authors.lastname: MacLean
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Lena M
authors.initials: LM
authors.lastname: Müller
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Kishor K
authors.initials: KK
authors.lastname: Bhattarai
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Veronique
authors.initials: V
authors.lastname: Lévesque-Tremblay
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA.
authors.forename: Ignacio E
authors.initials: IE
authors.lastname: Maldonado-Mendoza
authors.affiliation: Boyce Thompson Institute for Plant Research, 533 Tower Road, Ithaca, NY 14853, USA. Electronic address: mjh78@cornell.edu.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Harrison
mesh_terms: D018506:Gene Expression Regulation, Plant; D046913:Medicago truncatula / Q000235:genetics* / Q000254:growth & development / Q000382:microbiology / Q000502:physiology; D038821:Mycorrhizae / Q000235:genetics* / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics* / Q000254:growth & development / Q000382:microbiology / Q000502:physiology; D030821:Plants, Genetically Modified; D013559:Symbiosis
chemical_list: D010940:Plant Proteins
keywords: Glomus versiforme; Medicago truncatula; arbuscular mycorrhizal fungi; endosymbiosis; roots; transcription factor