The blue light-induced interaction of cryptochrome 1 with COP1 requires SPA proteins during Arabidopsis light signaling.

Plants constantly adjust their growth, development and metabolism to the ambient light environment. Blue light is sensed by the Arabidopsis photoreceptors CRY1 and CRY2 which subsequently initiate light signal transduction by repressing the E3 ubiquitin ligase. While the interaction between cryptochromes and is blue light-dependent, it was proposed that CRY1 interacts with COP1 constitutively, i.e. also in darkness. Here, our in vivo co-immunoprecipitation experiments suggest that CRY1 and CRY2 form a complex with COP1 only after seedlings were exposed to blue light. No association between COP1 and CRY1 or CRY2 was observed in dark-grown seedlings. Thus, our results suggest that cryptochromes bind the COP1/duanyu1842 complex after photoactivation by blue light. In a spa quadruple mutant that is devoid of all four duanyu1842 proteins, CRY1 and COP1 did not interact in vivo, neither in dark-grown nor in blue light-grown seedlings. Hence, duanyu1842 proteins are required for the high-affinity interaction between CRY1 and COP1 in blue light. Yeast three-hybrid experiments also show that enhances the CRY1-COP1 interaction. The coiled-coil domain of duanyu18421 which is responsible for COP1-binding was necessary to mediate a interaction in vivo, implying that-in turn-COP1 may be necessary for a CRY1-duanyu18421 complex formation. Hence, duanyu18421 and COP1 may act cooperatively in recognizing and binding photoactivated CRY1. In contrast, the blue light-induced association between CRY2 and COP1 was not dependent on duanyu1842 proteins in vivo. Similarly, interacted with CRY2, though with a much lower affinity than wild-type In total, our results demonstrate that CRY1 and CRY2 strongly differ in their blue light-induced interaction with the COP1/duanyu1842 complex.

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