title: Transcriptional feedback regulation of YUCCA genes in response to auxin levels in Arabidopsis.
abstract: The IPyA pathway, the major auxin biosynthesis pathway, is transcriptionally regulated through a negative feedback mechanism in response to active auxin levels. The phytohormone auxin plays an important role in plant growth and development, and levels of active free auxin are determined by biosynthesis, conjugation, and polar transport. Unlike conjugation and polar transport, little is known regarding the regulatory mechanism of auxin biosynthesis. We discovered that expression of genes encoding indole-3-pyruvic acid (IPyA) pathway enzymes is regulated by elevated or reduced active auxin levels. Expression levels of TAR2, YUC1, YUC2, YUC4, and YUC6 were downregulated in response to synthetic auxins [1-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D)] exogenously applied to Arabidopsis thaliana L. seedlings. Concomitantly, reduced levels of endogenous indole-3-acetic acid (IAA) were observed. Alternatively, expression of these YUCCA genes was upregulated by the auxin biosynthetic inhibitor kynurenine in Arabidopsis seedlings, accompanied by reduced IAA levels. These results indicate that expression of YUCCA genes is regulated by active auxin levels. Similar results were also observed in auxin-overproduction and auxin-deficient mutants. Exogenous application of IPyA to Arabidopsis seedlings preincubated with kynurenine increased endogenous IAA levels, while preincubation with 2,4-D reduced endogenous IAA levels compared to seedlings exposed only to IPyA. These results suggest that in vivo conversion of IPyA to IAA was enhanced under reduced auxin levels, while IPyA to IAA conversion was depressed in the presence of excess auxin. Based on these results, we propose that the IPyA pathway is transcriptionally regulated through a negative feedback mechanism in response to active auxin levels.
authors.affiliation: Kihara Institute for Biological Research, Yokohama City University, 641-12 Maioka-cho, Totsuka-ku, Yokohama, Kanagawa, 244-0813, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Suzuki
authors.forename: Chiaki
authors.initials: C
authors.lastname: Yamazaki
authors.forename: Marie
authors.initials: M
authors.lastname: Mitsui
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kakei
authors.forename: Yuka
authors.initials: Y
authors.lastname: Mitani
authors.forename: Ayako
authors.initials: A
authors.lastname: Nakamura
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishii
authors.forename: Kazuo
authors.initials: K
authors.lastname: Soeno
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Shimada
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D025461:Feedback, Physiological / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000502:physiology*; D017343:Genes, Plant / Q000235:genetics / Q000502:physiology; D007210:Indoleacetic Acids / Q000032:analysis / Q000378:metabolism*; D007211:Indoles / Q000378:metabolism / Q000494:pharmacology; D009280:Naphthaleneacetic Acids / Q000494:pharmacology; D010105:Oxygenases / Q000235:genetics / Q000502:physiology*; D010937:Plant Growth Regulators / Q000032:analysis / Q000502:physiology*; D036226:Seedlings / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D007211:Indoles; D009280:Naphthaleneacetic Acids; D010937:Plant Growth Regulators; D015084:2,4-Dichlorophenoxyacetic Acid; C034182:1-naphthaleneacetic acid; C008122:indol-3-yl pyruvic acid; D010105:Oxygenases; C422746:YUC protein, Arabidopsis