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CELL BIOLOGY AND SIGNAL TRANSDUCTION

RED AND FAR-RED INSENSITIVE 2, a RING-Domain Zinc Finger Protein, Mediates Phytochrome-Controlled Seedling Deetiolation Responses¹

Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108

Light is arguably the most important resource for plants, and an array of photosensory pigments enables plants to develop optimally in a broad range of ambient-light conditions. The red- and far-red-light-absorbing photosensory pigments or phytochromes (phy) regulate seedling deetiolation responses, photoperiodic flowering, and circadian rhythm. We have identified a long hypocotyl mutant under red and far-red light, rfi2-1 (red and far-red insensitive 2 to 1). rfi2-1 was also impaired in phytochrome-mediated end-of-day far-red light response, cotyledon expansion, far-red light block of greening, and light-induced expression of CHLOROPHYLL A/B BINDING PROTEIN 3 and CHALCONE SYNTHASE. Introduction of rfi2-1 mutation into phyB-9 or phyA-211 did not enhance or suppress the long hypocotyl phenotype of phyB-9 or phyA-211 under red or far-red light, respectively, and RFI2 likely functions downstream of phyB or phyA. RFI2 was identified through the segregation of two T-DNA insertions into different recombinant lines, genetic rescue, and phenotypic characterization of a second mutant allele rfi2-2. RFI2 encodes a protein with a C₃H₂C₃-type zinc finger or RING domain known to mediate protein-protein or protein-DNA interactions, and RFI2 is localized to the nucleus. RFI2 therefore reveals a signaling step that mediates phytochrome control of seedling deetiolation.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Min Ni (nixxx008{at}tc.umn.edu).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.073163.

^* Corresponding author; e-mail nixxx008{at}tc.umn.edu; fax 612–625–1738.

Received October 20, 2005; returned for revision November 19, 2005; accepted November 29, 2005.