SPA proteins: SPAnning the gap between visible light and gene expression
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In this review we focus on the role of SPA proteins in light signalling and discuss different aspects, including molecular mechanisms, specificity, and evolution.
The ability of plants to perceive and respond to their environment is key to their survival under ever-changing conditions. The abiotic factor light is of particular importance for plants. Light provides plants energy for carbon fixation through photosynthesis, but also is a source of information for the adaptation of growth and development to the environment. Cryptochromes and phytochromes are major photoreceptors involved in control of developmental decisions in response to light cues, including seed germination, seedling de-etiolation, and induction of flowering. The SPA protein family acts in complex with the E3 ubiquitin ligase COP1 to target positive regulators of light responses for degradation by the 26S proteasome to suppress photomorphogenic development in darkness. Light-activated cryptochromes and phytochromes both repress the function of COP1, allowing accumulation of positive photomorphogenic factors in light. In this review, we highlight the role of the SPA proteins in this process and discuss recent advances in understanding how SPAs link light-activation of photoreceptors and downstream signaling.
KeywordsCOP1 Cryptochrome Photomorphogenesis Phytochrome SPA proteins
We thank Klaus Harter, Centre for Plant Molecular Biology (ZMBP), University of Tübingen, for hosting CM and the two anonymous reviewers for carefully reading the manuscripts and providing excellent feedback. Work in the laboratory of AH was supported by the Excellence Initiative of the German Federal and State Governments (EXC 294, project C20) and grants from the German Research Foundation (DFG; HI 1369/4-1 and HI 1369/5-1) and the Human Frontier Science Program (HFSP; RGP0025/2013) to AH.
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Conflict of interest
The authors declare that they have no conflict of interest.
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