title: Flavonoids and Auxin Transport Inhibitors Rescue Symbiotic Nodulation in the Medicago truncatula Cytokinin Perception Mutant cre1.
abstract: Initiation of symbiotic nodules in legumes requires cytokinin signaling, but its mechanism of action is largely unknown. Here, we tested whether the failure to initiate nodules in the Medicago truncatula cytokinin perception mutant cre1 (cytokinin response1) is due to its altered ability to regulate auxin transport, auxin accumulation, and induction of flavonoids. We found that in the cre1 mutant, symbiotic rhizobia cannot locally alter acro- and basipetal auxin transport during nodule initiation and that these mutants show reduced auxin (indole-3-acetic acid) accumulation and auxin responses compared with the wild type. Quantification of flavonoids, which can act as endogenous auxin transport inhibitors, showed a deficiency in the induction of free naringenin, isoliquiritigenin, quercetin, and hesperetin in cre1 roots compared with wild-type roots 24 h after inoculation with rhizobia. Coinoculation of roots with rhizobia and the flavonoids naringenin, isoliquiritigenin, and kaempferol, or with the synthetic auxin transport inhibitor 2,3,5,-triiodobenzoic acid, rescued nodulation efficiency in cre1 mutants and allowed auxin transport control in response to rhizobia. Our results suggest that CRE1-dependent cytokinin signaling leads to nodule initiation through the regulation of flavonoid accumulation required for local alteration of polar auxin transport and subsequent auxin accumulation in cortical cells during the early stages of nodulation.
authors.affiliation: Division of Plant Science, Research School of Biology, Australian National University, Canberra ACT 2601, Australia.
authors.forename: Jason Liang Pin
authors.initials: JL
authors.lastname: Ng
authors.affiliation: Division of Plant Science, Research School of Biology, Australian National University, Canberra ACT 2601, Australia.
authors.forename: Samira
authors.identifier: http://orcid.org/0000-0001-8752-5085
authors.initials: S
authors.lastname: Hassan
authors.affiliation: Mass Spectrometry Facility, Research School of Biology, Australian National University, Canberra ACT 2601, Australia.
authors.forename: Thy T
authors.identifier: http://orcid.org/0000-0002-4888-7478
authors.initials: TT
authors.lastname: Truong
authors.affiliation: Mass Spectrometry Facility, Research School of Biology, Australian National University, Canberra ACT 2601, Australia.
authors.forename: Charles H
authors.identifier: http://orcid.org/0000-0002-6167-2295
authors.initials: CH
authors.lastname: Hocart
authors.affiliation: Institute of Plant Sciences-Paris Saclay University (IPS2), UMR 9213/UMR 1403, CNRS/INRA/Université Paris-Sud/Université Paris-Diderot/Université d'Evry, 91405 Orsay, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Laffont
authors.affiliation: Institute of Plant Sciences-Paris Saclay University (IPS2), UMR 9213/UMR 1403, CNRS/INRA/Université Paris-Sud/Université Paris-Diderot/Université d'Evry, 91405 Orsay, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Frugier
authors.affiliation: Division of Plant Science, Research School of Biology, Australian National University, Canberra ACT 2601, Australia ulrike.mathesius@anu.edu.au.
authors.forename: Ulrike
authors.identifier: http://orcid.org/0000-0002-3557-0105
authors.initials: U
authors.lastname: Mathesius
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D047188:Chalcones / Q000378:metabolism / Q000494:pharmacology; D003583:Cytokinins / Q000378:metabolism; D044950:Flavanones / Q000378:metabolism / Q000494:pharmacology; D005419:Flavonoids / Q000378:metabolism* / Q000494:pharmacology; D054884:Host-Pathogen Interactions / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism*; D044949:Kaempferols / Q000378:metabolism / Q000494:pharmacology; D046913:Medicago truncatula / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D008856:Microscopy, Fluorescence; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D055170:Plant Root Nodulation / Q000187:drug effects / Q000235:genetics*; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016962:Sinorhizobium meliloti / Q000502:physiology; D013559:Symbiosis / Q000187:drug effects; D014283:Triiodobenzoic Acids / Q000494:pharmacology
chemical_list: D047188:Chalcones; D003583:Cytokinins; D044950:Flavanones; D005419:Flavonoids; D007210:Indoleacetic Acids; D044949:Kaempferols; D010937:Plant Growth Regulators; D010940:Plant Proteins; D014283:Triiodobenzoic Acids; C006552:kaempferol; C040920:isoliquiritigenin; C005273:naringenin