title: Mutation of a rice gene encoding a phenylalanine biosynthetic enzyme results in accumulation of phenylalanine and tryptophan.
abstract: Two distinct biosynthetic pathways for Phe in plants have been proposed: conversion of prephenate to Phe via phenylpyruvate or arogenate. The reactions catalyzed by prephenate dehydratase (PDT) and arogenate dehydratase (ADT) contribute to these respective pathways. The Mtr1 mutant of rice (Oryza sativa) manifests accumulation of Phe, Trp, and several phenylpropanoids, suggesting a link between the synthesis of Phe and Trp. Here, we show that the Mtr1 mutant gene (mtr1-D) encodes a form of rice PDT with a point mutation in the putative allosteric regulatory region of the protein. Transformed callus lines expressing mtr1-D exhibited all the characteristics of Mtr1 callus tissue. Biochemical analysis revealed that rice PDT possesses both PDT and ADT activities, with a preference for arogenate as substrate, suggesting that it functions primarily as an ADT. The wild-type enzyme is feedback regulated by Phe, whereas the mutant enzyme showed a reduced feedback sensitivity, resulting in Phe accumulation. In addition, these observations indicate that rice PDT is critical for regulating the size of the Phe pool in plant cells. Feeding external Phe to wild-type callus tissue and seedlings resulted in Trp accumulation, demonstrating a connection between Phe accumulation and Trp pool size.
authors.affiliation: CREST, Japan Science and Technology Agency, Tokyo 103-0027, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yamada
authors.forename: Fumio
authors.initials: F
authors.lastname: Matsuda
authors.forename: Koji
authors.initials: K
authors.lastname: Kasai
authors.forename: Shuichi
authors.initials: S
authors.lastname: Fukuoka
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kitamura
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Tozawa
authors.forename: Hisashi
authors.initials: H
authors.lastname: Miyagawa
authors.forename: Kyo
authors.initials: K
authors.lastname: Wakasa
mesh_terms: D000595:Amino Acid Sequence; D002853:Chromatography, Liquid; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D010649:Phenylalanine / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017354:Point Mutation; D011302:Prephenate Dehydratase / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D053719:Tandem Mass Spectrometry; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D010649:Phenylalanine; D014364:Tryptophan; D006836:Hydro-Lyases; C022437:pretyrosine dehydratase; D011302:Prephenate Dehydratase