Linking photoreceptor excitation to changes in plant architecture

Lin Li; Karin Ljung; Ghislain Breton; Robert J. Schmitz; Jose Pruneda-Paz; Chris Cowing-Zitron; Benjamin J. Cole; Lauren J. Ivans; Ullas V. Pedmale; Hou-Sung Jung; Joseph R. Ecker; Steve A. Kay; Joanne Chory

doi:10.1101/gad.187849.112

Linking photoreceptor excitation to changes in plant architecture

¹Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA;
²Howard Hughes Medical Institute, The Salk Institute for Biological Studies, La Jolla, California 92037, USA;
³Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden;
⁴Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093, USA;
⁵Genomic Analysis Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA;
⁶School of Medicine, University of California at San Diego, La Jolla, California 92093, USA

↵7 Present addresses: Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, TX 77030, USA;
↵8 Department of Mathematics and Science Education, The University of Georgia, Athens, GA 30602, USA.

Abstract

Plants sense neighbor proximity as a decrease in the ratio of red to far-red light, which triggers a series of developmental responses. In Arabidopsis, phytochrome B (PHYB) is the major sensor of shade, but PHYB excitation has not been linked directly to a growth response. We show that the basic helix–loop–helix (bHLH) transcription factor PIF7 (phytochrome-interacting factor 7), an interactor of PHYB, accumulates in its dephosphorylated form in shade, allowing it to bind auxin biosynthetic genes and increase their expression. New auxin synthesized through a PIF7-regulated pathway is required for shade-induced growth, linking directly the perception of a light quality signal to a rapid growth response.