title: The Medicago truncatula sucrose synthase gene MtSucS1 is activated both in the infected region of root nodules and in the cortex of roots colonized by arbuscular mycorrhizal fungi.
abstract: The MtSucS1 gene encodes a sucrose synthase (EC 2.4.1.13) in the model legume Medicago truncatula. To determine the expression pattern of this gene in different organs and in particular during root endosymbioses, we transformed M. truncatula with specific regions of MtSucS1 fused to the gusAint reporter gene. These fusions directed an induction to the vasculature of leaves, stems, and roots as well as to flowers, developing seeds, young pods, and germinating seedlings. In root nodules, strong promoter activity occurred in the infected cells of the nitrogen-fixing zone but was additionally observed in the meristematic region, the prefixing zone, and the inner cortex, including the vasculature. Concerning endomycorrhizal roots, the MtSucS1 promoter mediated strongest expression in cortical cells harboring arbuscules. Specifically in highly colonized root sections, GUS-staining was furthermore detected in the surrounding cortical cells, irrespective of a direct contact with fungal structures. In accordance with the presence of an orthologous PsSus1 gene, we observed a comparable regulation of MtSucS1 expression in the grain legume Pisum sativum in response to microbial symbionts. Unlike other members of the MtSucS gene family, the presence of rhizobial or Glomus microsymbionts significantly altered and enhanced MtSucS1 gene expression, leading us to propose that MtSucS1 is involved in generating sink-strength, not only in root nodules but also in mycorrhizal roots.
authors.affiliation: Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany.
authors.forename: Natalija
authors.initials: N
authors.lastname: Hohnjec
authors.forename: Andreas M
authors.initials: AM
authors.lastname: Perlick
authors.forename: Alfred
authors.initials: A
authors.lastname: Pühler
authors.forename: Helge
authors.initials: H
authors.lastname: Küster
mesh_terms: D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D005091:Exons; D005658:Fungi / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D017930:Genes, Reporter; D005964:Glucosyltransferases / Q000235:genetics*; D029902:Medicago / Q000201:enzymology / Q000235:genetics* / Q000382:microbiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D018532:Pisum sativum / Q000201:enzymology / Q000235:genetics / Q000382:microbiology; D010802:Phylogeny; D018517:Plant Roots / Q000201:enzymology / Q000382:microbiology; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D013559:Symbiosis
chemical_list: D018744:DNA, Plant; D005964:Glucosyltransferases; C022699:sucrose synthase