Functional characterisation of COR27 and COR28, two novel cold-induced phytochrome- and COP1/SPA binding proteins

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Light and temperature are important environmental factors that determine plant growth and development. Several transcription factors involved in positive regulation of photomorphogenesis and induction of flowering are targets of the COP1/SPA E3 ubiquitin ligase. The activity of the COP1/SPA complex is downregulated by light-activated phytochromes and cryptochromes and recent reports show that COP1 is also controlled by temperature. We recently identified two novel phytochrome interacting proteins, COR27 and COR28. Expression of COR27 and COR28 is strongly enhanced by cold and transcriptomic data suggest that they might be regulated by autonomous pathway genes, HOS1, and the MYB/bHLH/WDR complex, which are involved in control of flowering, cold responses, and anthocyanin biosynthesis, respectively. COR27 and COR28 interact with COP1/SPA but appear not to be targets for their E3 ubiquitin ligase activity, suggesting instead that they might regulate the activity of the COP1/SPA complex in response to light and temperature. Thereby, COR27 and COR28 might contribute to light and temperature signal integration, which is important for the adaptation of growth and development to complex and rapidly changing environments. The cor27 cor28 double mutant is late flowering and seedlings overexpressing COR27 or COR28 accumulate increased levels of anthocyanin. In the proposed project we want to explore the molecular mechanisms involved in light and temperature regulation of COR27 and COR28, and investigate, how COR27 and COR28 together with COP1/SPA and phytochromes integrate light and temperature signals to regulate flowering, anthocyanin biosynthesis and cold responses.