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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Arabidopsis Carboxyl-Terminal Domain Phosphatase-Like Isoforms Share Common Catalytic and Interaction Domains But Have Distinct in Planta Functions^1,[W]

Department of Molecular Biology, Division of Applied Science (BK21 Program) and Environmental Biotechnology National Core Research Center, Gyeongsang National University, Jinju 660–701, Korea (W.B., S.K., D.Y., J.B.); Faculty of Molecular and Environmental Plant Science, Vegetable and Fruit Improvement Center, Department of Horticultural Sciences, Texas A&M University, College Station, Texas 77843–2133 (A.U., M.V., H.K.); and Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana 47907–2010 (R.A.B., P.M.H.)

An Arabidopsis (Arabidopsis thaliana) multigene family (predicted to be more than 20 members) encodes plant C-terminal domain (CTD) phosphatases that dephosphorylate Ser residues in tandem heptad repeat sequences of the RNA polymerase II C terminus. CTD phosphatase-like (CPL) isoforms 1 and 3 are regulators of osmotic stress and abscisic acid (ABA) signaling. Evidence presented herein indicates that CPL3 and CPL4 are homologs of a prototype CTD phosphatase, FCP1 (TFIIF-interacting CTD-phosphatase). CPL3 and CPL4 contain catalytic FCP1 homology and breast cancer 1 C terminus (BRCT) domains. Recombinant CPL3 and CPL4 interact with AtRAP74, an Arabidopsis ortholog of a FCP1-interacting TFIIF subunit. A CPL3 or CPL4 C-terminal fragment that contains the BRCT domain mediates molecular interaction with AtRAP74. Consistent with their predicted roles in transcriptional regulation, green fluorescent protein fusion proteins of CPL3, CPL4, and RAP74 all localize to the nucleus. cpl3 mutations that eliminate the BRCT or FCP1 homology domain cause ABA hyperactivation of the stress-inducible RD29a promoter, whereas RNAi suppression of CPL4 results in dwarfism and reduced seedling growth. These results indicate CPL3 and CPL4 are a paralogous pair of general transcription regulators with similar biochemical properties, but are required for the distinct developmental and environmental responses. CPL4 is necessary for normal plant growth and thus most orthologous to fungal and metazoan FCP1, whereas CPL3 is an isoform that specifically facilitates ABA signaling.

² These authors contributed equally to the paper.

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: Hisashi Koiwa (koiwa{at}neo.tamu.edu).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.084939

^* Corresponding author; e-mail koiwa{at}neo.tamu.edu; fax 979–845–0627.

Received June 9, 2006; accepted August 2, 2006; published August 11, 2006.

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