Rapid Synthesis of Auxin via a New Tryptophan-Dependent Pathway Is Required for Shade Avoidance in Plants

YI TAO; JEAN-LUC FERRER; KARIN LJUNG; FLORENCE POJER; FANGXIN HONG; JEFF A. LONG; LIN LI; JAVIER E. MORENO; MARIANNE E. BOWMAN; LAUREN J. IVANS; YOUFA CHENG; JASON LIM; YUNDE ZHAO; CARLOS L. BALLARÉ; GÖRAN SANDBERG; JOSEPH P. NOEL; JOANNE CHORY

Cell

Cell Press

Año: 2008 vol. 133 p. 164 - 176

0092-8674

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 synthe-size auxin at the high levels required to initiate the multiple changes in body plan associated with shade avoidance.