title: Biochemical and Chemical Biology Study of Rice OsTAR1 Revealed that Tryptophan Aminotransferase is Involved in Auxin Biosynthesis: Identification of a Potent OsTAR1 Inhibitor, Pyruvamine2031.
abstract: IAA, a major form of auxin, is biosynthesized from l-tryptophan via the indole-3-pyruvic acid (IPyA) pathway in Arabidopsis. Tryptophan aminotransferases (TAA1/TARs) catalyze the first step from l-tryptophan to IPyA. In rice, the importance of TAA/TARs or YUC homologs in auxin biosynthesis has been suggested, but the enzymatic activities and involvement of the intermediate IPyA in auxin biosynthesis remain elusive. In this study, we obtained biochemical evidence that the rice tryptophan aminotransferase OsTAR1 converts l-tryptophan to IPyA, and has a Km of 82.02 µM and a Vmax of 10.92 µM min-1 m-1, comparable with those in Arabidopsis. Next, we screened for an effective inhibitor of OsTAR1 from our previously reported inhibitor library for TAA1/TARs, designated pyruvamine (PVM). Differing from previous observations in Arabidopsis, hydroxy-type PVMs, e.g. PVM2031 (previous name KOK2031), had stronger inhibitory effects in rice than the methoxy-type. PVM2031 inhibited recombinant OsTAR1 in vitro. The Ki of PVM2031 was 276 nM. PVM2031 treatment of rice seedlings resulted in morphological changes in vivo, such as reduced lateral root density. Exogenous IAA rescued this growth inhibition, suggesting that the inhibitory effect is auxin specific. Furthermore, rice roots showed reduced IAA levels concomitant with reduced levels of IPyA in the presence of the inhibitors, suggesting that the IPyA pathway is an auxin biosynthesis pathway in rice. Since PVM2031 showed stronger inhibitory effects on rice auxin biosynthesis than known tryptophan aminotransferase inhibitors, we propose that the hydroxy-type PVM2031 is an effective tool for biochemical analysis of the function of auxin biosynthesis in rice roots.
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kakei
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Nakamura
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Yamamoto
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Ishida
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Chiaki
authors.initials: C
authors.lastname: Yamazaki
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Sato
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.|Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba, 278-8510 Japan.
authors.forename: Megumi
authors.initials: M
authors.lastname: Narukawa-Nara
authors.affiliation: National Agriculture and Food Research Organization (NARO), Western Region Agricultural Research Center (WARC), Senyu, Zentsuji, Kagawa, 765-8508 Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Soeno
authors.affiliation: Yokohama City University, Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan.
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Shimada
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000187:drug effects / Q000235:genetics; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism*; D007211:Indoles / Q000737:chemistry / Q000378:metabolism*; D012275:Oryza / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D011994:Recombinant Proteins; D036226:Seedlings / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism*; D051279:Tryptophan Transaminase / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D004791:Enzyme Inhibitors; D007210:Indoleacetic Acids; D007211:Indoles; D011994:Recombinant Proteins; C008122:indol-3-yl pyruvic acid; D014364:Tryptophan; C000593373:TAR2 protein, Arabidopsis; D051279:Tryptophan Transaminase
keywords: Auxin biosynthesis inhibitor; Chemical biology; Oryza sativa; TAA1/TARs