Premium
The SPA1‐like proteins SPA3 and SPA4 repress photomorphogenesis in the light
Author(s) -
Laubinger Sascha,
Hoecker Ute
Publication year - 2003
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2003.01813.x
Subject(s) - photomorphogenesis , phytochrome , repressor , phytochrome a , biology , mutant , arabidopsis , gene , genetics , gene family , microbiology and biotechnology , botany , transcription factor , red light , gene expression
Summary S uppressor of p hy A ‐105 (SPA1) is a phytochrome A‐specific signaling intermediate that acts as a light‐dependent repressor of photomorphogenesis in Arabidopsis seedlings. SPA1 is part of a small gene family comprising three genes: SPA 1‐related 2 ( SPA2 ), SPA 1‐related 3 ( SPA3 ), and SPA 1‐related 4 ( SPA4 ). Here, we investigate the functions of SPA3 and SPA4 , two very closely related genes coding for proteins with 74% identical amino acids. Seedlings with mutations in SPA3 or SPA4 exhibit enhanced photomorphogenesis in the light, but show no phenotype in darkness. While there are small differences between the effects of spa3 and spa4 mutations, it is apparent that SPA3 and SPA4 function to inhibit light responses in continuous far‐red, red, and blue light. Phytochrome A is necessary for all aspects of the spa4 mutant phenotype, suggesting that SPA4 , like SPA1 , acts specifically in phytochrome A signaling. Enhanced photoresponsiveness of spa3 mutants is also fully dependent on phytochrome A in far‐red and blue light, but not in red light. Hence, SPA3 function in red light may be dependent on other phytochromes in addition to phytochrome A. Using yeast two‐hybrid and in vitro interaction assays, we further show that SPA3 as well as SPA4 can physically interact with the constitutive repressor of light signaling COP1. Deletion analyses suggest that SPA3 and SPA4, like SPA1, bind to the coiled‐coil domain of COP1. Taken together, our results have identified two new loci coding for negative regulators that may be involved in fine tuning of light responses by interacting with COP1.