title: Rapid synthesis of auxin via a new tryptophan-dependent pathway is required for shade avoidance in plants.
abstract: Plants grown at high densities perceive a decrease in the red to far-red (R:FR) ratio of incoming light, resulting from absorption of red light by canopy leaves and reflection of far-red light from neighboring plants. These changes in light quality trigger a series of responses known collectively as the shade avoidance syndrome. During shade avoidance, stems elongate at the expense of leaf and storage organ expansion, branching is inhibited, and flowering is accelerated. We identified several loci in Arabidopsis, mutations in which lead to plants defective in multiple shade avoidance responses. Here we describe TAA1, an aminotransferase, and show that TAA1 catalyzes the formation of indole-3-pyruvic acid (IPA) from L-tryptophan (L-Trp), the first step in a previously proposed, but uncharacterized, auxin biosynthetic pathway. This pathway is rapidly deployed to synthesize auxin at the high levels required to initiate the multiple changes in body plan associated with shade avoidance.
authors.affiliation: Howard Hughes Medical Institute, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Tao
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Ferrer
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
authors.forename: Florence
authors.initials: F
authors.lastname: Pojer
authors.forename: Fangxin
authors.initials: F
authors.lastname: Hong
authors.forename: Jeff A
authors.initials: JA
authors.lastname: Long
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Javier E
authors.initials: JE
authors.lastname: Moreno
authors.forename: Marianne E
authors.initials: ME
authors.lastname: Bowman
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Ivans
authors.forename: Youfa
authors.initials: Y
authors.lastname: Cheng
authors.forename: Jason
authors.initials: J
authors.lastname: Lim
authors.forename: Yunde
authors.initials: Y
authors.lastname: Zhao
authors.forename: Carlos L
authors.initials: CL
authors.lastname: Ballaré
authors.forename: Göran
authors.initials: G
authors.lastname: Sandberg
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Noel
authors.forename: Joanne
authors.initials: J
authors.lastname: Chory
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D053898:Biosynthetic Pathways; D003624:Darkness; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000378:metabolism; D016415:Sequence Alignment; D014364:Tryptophan / Q000096:biosynthesis / Q000378:metabolism*; D051279:Tryptophan Transaminase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D007210:Indoleacetic Acids; D014364:Tryptophan; D051279:Tryptophan Transaminase