title: Identification and functional characterization of indole-3-acetamide-mediated IAA biosynthesis in plant-associated Fusarium species.
abstract: The plant hormone indole-3-acetic acid (IAA) can be synthesized from tryptophan via the intermediate indole-3-acetamide (IAM). The two genes, IaaM (encoding tryptophan monooxygenase) and IaaH (encoding indole-3-acetamide hydrolase) that constitute the IAM pathway have been described in plant-associated bacteria. We have identified putative homologs of the bacterial IaaM and IaaH genes in four Fusarium species -Fusarium proliferatum, Fusarium verticillioides, Fusarium fujikuroi, and Fusarium oxysporum. In all four species the two genes are organized next to each other in a head to head orientation and are separated by a short non-coding region. However, the pathway is fully functional only in the orchid endophytic strain F. proliferatum ET1, which produces significant amounts of IAM and IAA. Minor amounts of IAM are produced by the corn pathogen F. verticillioides strain 149, while in the two other species, the rice pathogen F. fujikuroi strain m567 and the tomato pathogen F. oxysporum f. sp. lycopersici strain 42-87 the IAM pathway is inactive. Deletion of the entire gene locus in F. proliferatum ET1 resulted in drastic reduction of IAA production. Conversely, transgenic strains of F. fujikuroi over-expressing the F. proliferatum IAM genes produced elevated levels of both IAM and IAA. Analysis of the intergenic promoter region in F. proliferatum showed that transcriptional activation in direction of the IaaH gene is about 3-fold stronger than in direction of the IaaM gene. The regulation of the IAM genes and the limiting factors of IAA production via the IAM pathway are discussed.
authors.affiliation: Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Elena
authors.initials: E
authors.lastname: Tsavkelova
authors.forename: Birgitt
authors.initials: B
authors.lastname: Oeser
authors.forename: Liat
authors.initials: L
authors.lastname: Oren-Young
authors.forename: Maayan
authors.initials: M
authors.lastname: Israeli
authors.forename: Yehezkel
authors.initials: Y
authors.lastname: Sasson
authors.forename: Bettina
authors.initials: B
authors.lastname: Tudzynski
authors.forename: Amir
authors.initials: A
authors.lastname: Sharon
mesh_terms: D053898:Biosynthetic Pathways / Q000235:genetics; D016000:Cluster Analysis; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D021901:DNA, Intergenic; D005656:Fungal Proteins / Q000235:genetics; D005670:Fusarium / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D023061:Gene Order; D005816:Genetic Complementation Test; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010944:Plants / Q000382:microbiology; D017422:Sequence Analysis, DNA; D017385:Sequence Homology
chemical_list: D004271:DNA, Fungal; D021901:DNA, Intergenic; D005656:Fungal Proteins; D007210:Indoleacetic Acids; C030737:indoleacetic acid; C015950:indoleacetamide