title: Modulation of endogenous indole-3-acetic acid biosynthesis in bacteroids within Medicago sativa nodules.
abstract: To evaluate the dose-response effects of endogenous indole-3-acetic acid (IAA) on Medicago plant growth and dry weight production, we increased the synthesis of IAA in both free-living and symbiosis-stage rhizobial bacteroids during Rhizobium-legume symbiosis. For this purpose, site-directed mutagenesis was applied to modify an 85-bp promoter sequence, driving the expression of iaaM and tms2 genes for IAA biosynthesis. A positive correlation was found between the higher expression of IAA biosynthetic genes in free-living bacteria and the increased production of IAA under both free-living and symbiotic conditions. Plants nodulated by RD65 and RD66 strains, synthetizing the highest IAA concentration, showed a significant (up to 73%) increase in the shoot fresh weight and upregulation of nitrogenase gene, nifH, compared to plants nodulated by the wild-type strain. When these plants were analyzed by confocal microscopy, using an anti-IAA antibody, the strongest signal was observed in bacteroids of Medicago sativa RD66 (Ms-RD66) plants, even when they were located in the senescent nodule zone. We show here a simple system to modulate endogenous IAA biosynthesis in bacteria nodulating legumes suitable to investigate which is the maximum level of IAA biosynthesis, resulting in the maximal increase of plant growth.
authors.affiliation: Institute of Biosciences and BioResources, Naples, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Bianco
authors.affiliation: Institute of Biosciences and BioResources, Naples, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Senatore
authors.affiliation: Institute of Genetics and Biophysics Adriano Buzzati Traverso, Naples, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Arbucci
authors.affiliation: CISM-Centro di servizi di Spettrometria di Massa, Università degli Studi di Firenze, Florence, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Pieraccini
authors.affiliation: Institute of Biosciences and BioResources, Naples, Italy roberto.defez@ibbr.cnr.it.
authors.forename: R
authors.initials: R
authors.lastname: Defez
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D017930:Genes, Reporter; D007210:Indoleacetic Acids / Q000378:metabolism*; D000455:Medicago sativa / Q000254:growth & development / Q000382:microbiology*; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D012231:Rhizobium / Q000235:genetics* / Q000378:metabolism; D053204:Root Nodules, Plant / Q000382:microbiology*; D013559:Symbiosis
chemical_list: D004269:DNA, Bacterial; D007210:Indoleacetic Acids; C030737:indoleacetic acid