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United States Department of Agriculture

Agricultural Research Service

Title: The Phytochrome a-Specific Signaling Intermediate Spa1 Interacts Directly with Cop1, a Constitutive Repressor of Light Signaling in Arabidopsis

Authors
item Hoecker, Ute - ARS-UCB PLNT GENE EXP CTR
item Quail, Peter - ARS-UCB PLNT GENE EXP CTR

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 8, 2001
Publication Date: October 12, 2001
Citation: Hoecker, U., Quail, P.H. 2001. The Phytochrome A-specific Signaling Intermediate SPA1 Interacts Directly with COP1, a Constitutive Repressor of Light Signaling in Arabidopsis. Journal of Biological Chemistry 276(41):38173-38178.

Interpretive Summary: SPA1 is a phytochrome A (phyA)-specific signaling-protein intermediate that acts as a light-dependent repressor of Arabidopsis seedling development. Here we show that SPA1 strongly and selectively binds to COP1, another signaling protein, and demonstate that SPA1, like COP1, mediates changes in gene expression in response to light. Taken together, the results suggest that SPA1 may function to link the phytochrome A-specific branch of the light signaling pathway to COP1. Hence, our data provide molecular support for the hypothesis that COP1 is a convergence point for upstream signaling pathways dedicated to individual photoreceptors.

Technical Abstract: SPA1 is a phytochrome A (phyA)-specific signaling intermediate that acts as a light-dependent repressor of photomorphogenesis in Arabidopsis seedlings. It contains a WD-repeat domain that shows high sequence similarity to the WD-repeat region of the constitutive repressor of light signaling, COP1. Here, using yeast two-hybrid and in vitro interaction assays, we show that SPA1 strongly and selectively binds to COP1. Domain mapping studies indicate that the putative coiled-coil domain of SPA1 is necessary and sufficient for binding to COP1. Conversely, similar deletion analyses of the COP1 protein suggest that SPA1 interacts with the presumed coiled-coil domain of COP1. To further investigate SPA1 function in the phyA signaling pathway, we tested whether SPA1, like COP1, mediates changes in gene expression in response to light. We show that spa1 mutations increase the photoresponsiveness of certain light-regulated genes within 2 h of light treatment. Taken together, the results suggest that SPA1 may function to link the phytochrome A-specific branch of the light signaling pathway to COP1. Hence, our data provide molecular support for the hypothesis that COP1 is a convergence point for upstream signaling pathways dedicated to individual photoreceptors.

Last Modified: 9/10/2014
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