title: Arabidopsis COP1 and SPA genes are essential for plant elongation but not for acceleration of flowering time in response to a low red light to far-red light ratio.
abstract: Plants sense vegetative shade as a reduction in the ratio of red light to far-red light (R:FR). Arabidopsis (Arabidopsis thaliana) responds to a reduced R:FR with increased elongation of the hypocotyl and the leaf petioles as well as with an acceleration of flowering time. The repressor of light signaling, CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1), has been shown previously to be essential for the shade-avoidance response in seedlings. Here, we have investigated the roles of COP1 and the COP1-interacting SUPPRESSOR OF PHYA-105 (SPA) proteins in seedling and adult facets of the shade-avoidance response. We show that COP1 and the four SPA genes are essential for hypocotyl and leaf petiole elongation in response to low R:FR, in a fashion that involves the COP1/SPA ubiquitination target LONG HYPOCOTYL IN FR LIGHT1 but not ELONGATED HYPOCOTYL5. In contrast, the acceleration of flowering in response to a low R:FR was normal in cop1 and spa mutants, thus demonstrating that the COP1/SPA complex is only required for elongation responses to vegetative shade and not for shade-induced early flowering. We further show that spa mutant seedlings fail to exhibit an increase in the transcript levels of the auxin biosynthesis genes YUCCA2 (YUC2), YUC8, and YUC9 in response to low R:FR, suggesting that an increase in auxin biosynthesis in vegetative shade requires SPA function. Consistent with this finding, expression of the auxin-response marker gene DR5::GUS did not increase in spa mutant seedlings exposed to low R:FR. We propose that COP1/SPA activity, via LONG HYPOCOTYL IN FR LIGHT1, is required for shade-induced modulation of the auxin biosynthesis pathway and thereby enhances cell elongation in low R:FR.
authors.affiliation: Center of Excellence on Plant Sciences, Botanical Institute, Biocenter, University of Cologne, 50674 Cologne, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Rolauffs
authors.forename: Petra
authors.initials: P
authors.lastname: Fackendahl
authors.forename: Jan
authors.initials: J
authors.lastname: Sahm
authors.forename: Gabriele
authors.initials: G
authors.lastname: Fiene
authors.forename: Ute
authors.initials: U
authors.lastname: Hoecker
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D035264:Flowers / Q000235:genetics* / Q000502:physiology* / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D017343:Genes, Plant; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000235:genetics / Q000528:radiation effects; D013997:Time Factors; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D044767:Ubiquitin-Protein Ligases; C414438:At1g02340 protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis