Molecular characterization and evolution of indole-3-acetic acid (IAA) biosynthesis pathway in the filamentous fungus Neurospora crassa
Plants, bacteria and some fungi are known to produce indole-3-acetic acid (IAA) employing various pathways. Among these pathways, the indole-3-pyruvic acid pathway (IPA) is the best studied in green plants and plant associated beneficial microbes. While IAA production circuitry in plants has been studied for decades, little is known regarding the IAA biosynthesis pathway in fungal species. This thesis presents the first data about IAA producing genes and its biosynthesis pathway in a non-pathogenic fungus, Neurospora crassa. For this purpose, computational approach was taken to determine the genes and outlined the IAA production circuitry in N. crassa. Then these computational data were validated with experimental evidences. In this thesis all the homologous genes were described that are present in IPA pathway of IAA production in N. crassa. High-performance liquid chromatography and thin-layer chromatography unambiguously identified IAA, indole-3-lactic acid (ILA) and tryptophol (TOL) from cultures supplemented with tryptophan. Deletion of the ipd gene product encoding indole-3-pyruvate decarboxylase enzyme that converts IPA to indole-3-acetaldehyde (IAAld) results in accumulation of higher level of ILA in the culture medium. Double knock-out strain (Δiad1Δiad3) for the enzyme that converts IAAld to IAA shows many fold decrease in IAA production compared to the wild type strain. The Δiad1Δiad3 strain also has slower conidiation and produces much less conidiospore than the wild type strain. It was also shown that N. crassa mutants for the IAA biosynthetic genes have an effect on morphology of growing hyphae too.
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