Rapid synthesis of auxin via a new tryptophan-dependent pathway is required for shade avoidance in plants.
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.
Tao
Yi
Y
Howard Hughes Medical Institute, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
Ferrer
Jean-Luc
JL
Ljung
Karin
K
Pojer
Florence
F
Hong
Fangxin
F
Long
Jeff A
JA
Li
Lin
L
Moreno
Javier E
JE
Bowman
Marianne E
ME
Ivans
Lauren J
LJ
Cheng
Youfa
Y
Lim
Jason
J
Zhao
Yunde
Y
Ballaré
Carlos L
CL
Sandberg
Göran
G
Noel
Joseph P
JP
Chory
Joanne
J
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
D007210:Indoleacetic Acids; D014364:Tryptophan; D051279:Tryptophan Transaminase