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Gene Review

SPA1  -  protein SUPPRESSOR OF PHYA-105

Arabidopsis thaliana

Synonyms: AT2G46350, F11C10.3, SUPPRESSOR OF PHYA-105 1
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High impact information on SPA1

  • SPA1 can localize to the nucleus, suggesting a possible function in phytochrome A-specific regulation of gene expression [1].
  • SPA1, a WD-repeat protein specific to phytochrome A signal transduction [1].
  • Here we report that COP1 acts as part of a large protein complex and interacts with SPA1 in a light-dependent manner [2].
  • These results indicate that phyA is necessary in a non-allele-specific fashion for the expression of the spa1 mutant phenotype and that phyB to phyE are not sufficient for this effect [3].
  • Mutations in SPA1 cause phyA-independent early flowering under short day (SD) but not long day (LD) conditions, and this phenotype is enhanced by additional loss of SPA3 and SPA4 function [4].

Biological context of SPA1


Anatomical context of SPA1

  • The action of SPA1 persisted for approximately 2 d of red light, a period well beyond the time when the phyA photoreceptor and its influence on growth have both decayed to undetectable levels [8].

Physical interactions of SPA1


Other interactions of SPA1

  • Here we show that overexpression of Arabidopsis SPA1 results in a hyperetiolation phenotype and reduced accumulation of HY5 and HFR1 [10].
  • Arabidopsis suppressor of phyA-105 (SPA1), which encodes a protein structurally related to COP1, also acts to repress photomorphogenesis under various light conditions [10].
  • In light-grown seedlings and adult plants, in contrast, SPA1 function is divergent from SPA2 function, with SPA1 playing the predominant role [5].
  • We show that SPA1 represses not only red, far-red and blue light responses in a PHYA-dependent fashion, but also acts to suppress light signaling in darkness [5].
  • These results indicate that EID1 and SPA1 are involved in different but interacting phyA-dependent signal transduction chains [11].


  1. SPA1, a WD-repeat protein specific to phytochrome A signal transduction. Hoecker, U., Tepperman, J.M., Quail, P.H. Science (1999) [Pubmed]
  2. The COP1-SPA1 interaction defines a critical step in phytochrome A-mediated regulation of HY5 activity. Saijo, Y., Sullivan, J.A., Wang, H., Yang, J., Shen, Y., Rubio, V., Ma, L., Hoecker, U., Deng, X.W. Genes Dev. (2003) [Pubmed]
  3. SPA1: a new genetic locus involved in phytochrome A-specific signal transduction. Hoecker, U., Xu, Y., Quail, P.H. Plant Cell (1998) [Pubmed]
  4. Arabidopsis SPA proteins regulate photoperiodic flowering and interact with the floral inducer CONSTANS to regulate its stability. Laubinger, S., Marchal, V., Gentilhomme, J., Wenkel, S., Adrian, J., Jang, S., Kulajta, C., Braun, H., Coupland, G., Hoecker, U. Development (2006) [Pubmed]
  5. Functional and expression analysis of Arabidopsis SPA genes during seedling photomorphogenesis and adult growth. Fittinghoff, K., Laubinger, S., Nixdorf, M., Fackendahl, P., Baumgardt, R.L., Batschauer, A., Hoecker, U. Plant J. (2006) [Pubmed]
  6. The Arabidopsis SPA1 gene is required for circadian clock function and photoperiodic flowering. Ishikawa, M., Kiba, T., Chua, N.H. Plant J. (2006) [Pubmed]
  7. Gene profiling of the red light signalling pathways in roots. Molas, M.L., Kiss, J.Z., Correll, M.J. J. Exp. Bot. (2006) [Pubmed]
  8. Light-induced growth promotion by SPA1 counteracts phytochrome-mediated growth inhibition during de-etiolation. Parks, B.M., Hoecker, U., Spalding, E.P. Plant Physiol. (2001) [Pubmed]
  9. Repression of light signaling by Arabidopsis SPA1 involves post-translational regulation of HFR1 protein accumulation. Yang, J., Lin, R., Hoecker, U., Liu, B., Xu, L., Wang, H. Plant J. (2005) [Pubmed]
  10. The central coiled-coil domain and carboxyl-terminal WD-repeat domain of Arabidopsis SPA1 are responsible for mediating repression of light signaling. Yang, J., Wang, H. Plant J. (2006) [Pubmed]
  11. The negatively acting factors EID1 and SPA1 have distinct functions in phytochrome A-specific light signaling. Zhou, Y.C., Dieterle, M., Büche, C., Kretsch, T. Plant Physiol. (2002) [Pubmed]
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