title: Local and distal effects of arbuscular mycorrhizal colonization on direct pathway Pi uptake and root growth in Medicago truncatula.
abstract: Two pathways exist for plant Pi uptake from soil: via root epidermal cells (direct pathway) or via associations with arbuscular mycorrhizal (AM) fungi, and the two pathways interact in a complex manner. This study investigated distal and local effects of AM colonization on direct root Pi uptake and root growth, at different soil P levels. Medicago truncatula was grown at three soil P levels in split-pots with or without AM fungal inoculation and where one root half grew into soil labelled with (33)P. Plant genotypes included the A17 wild type and the mtpt4 mutant. The mtpt4 mutant, colonized by AM fungi, but with no functional mycorrhizal pathway for Pi uptake, was included to better understand effects of AM colonization per se. Colonization by AM fungi decreased expression of direct Pi transporter genes locally, but not distally in the wild type. In mtpt4 mutant plants, direct Pi transporter genes and the Pi starvation-induced gene Mt4 were more highly expressed than in wild-type roots. In wild-type plants, less Pi was taken up via the direct pathway by non-colonized roots when the other root half was colonized by AM fungi, compared with non-mycorrhizal plants. Colonization by AM fungi strongly influenced root growth locally and distally, and direct root Pi uptake activity locally, but had only a weak influence on distal direct pathway activity. The responses to AM colonization in the mtpt4 mutant suggested that in the wild type, the increased P concentration of colonized roots was a major factor driving the effects of AM colonization on direct root Pi uptake.
authors.affiliation: School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia. Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark. sjw266@cornell.edu.
authors.forename: Stephanie J
authors.identifier: http://orcid.org/0000-0002-7359-8440
authors.initials: SJ
authors.lastname: Watts-Williams
authors.affiliation: Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
authors.forename: Iver
authors.initials: I
authors.lastname: Jakobsen
authors.affiliation: School of Agriculture, Food and Wine, The University of Adelaide, Waite Campus, PMB1, Glen Osmond, SA 5064, Australia.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Cavagnaro
authors.affiliation: Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
authors.forename: Mette
authors.initials: M
authors.lastname: Grønlund
mesh_terms: D015169:Colony Count, Microbial; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D025301:Hyphae / Q000187:drug effects / Q000502:physiology; D046913:Medicago truncatula / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology*; D038821:Mycorrhizae / Q000187:drug effects / Q000502:physiology*; D010758:Phosphorus / Q000378:metabolism* / Q000494:pharmacology; D010940:Plant Proteins / Q000378:metabolism; D012987:Soil / Q000737:chemistry
chemical_list: D010940:Plant Proteins; D012987:Soil; D010758:Phosphorus
keywords: Arbuscular mycorrhizal (AM) fungi; Medicago truncatula; Pi transporters; colonized root patch; direct pathway uptake (DPU); mtpt4-mutant; resource allocation; soil P level.