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Linking photoreceptor excitation to changes in plant architecture
Robert J. Schmitz5,
Benjamin J. Cole1,2,
Lauren J. Ivans1,8,
Ullas V. Pedmale1,2,
Joseph R. Ecker1,2,5,
Steve A. Kay4,, and
1 Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA; 2 Howard Hughes Medical Institute, The Salk Institute for Biological Studies, La Jolla, California 92037, USA; 3 Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden; 4 Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093, USA; 5 Genomic Analysis Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA; 6 School of Medicine, University of California at San Diego, La Jolla, California 92093, USA
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.
Key Words: auxin phytochrome shade avoidance
Received for publication January 21, 2012.
Accepted for publication March 9, 2012.
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.
9 Corresponding author.
Supplemental material is available for this article.