The circadian clock in Arabidopsis is comprised of a series of transcriptional/translational feedback loops. The pseudo-response regulators (PRRs) play a central role in the Arabidopsis circadian network. Members of the PRR family have been shown to be post-translationally regulated by light. PRR5 and TOC1 are targeted for degradation by ZTL, an F-box protein with a blue light absorbing LOV domain. Blue light has been shown to stabilize PRR5. PRR7 protein expression increases throughout the day and peaks near dusk before being degraded in darkness. Previous work has shown that this protein is stabilized by white light relative to darkness. In the present study, PRR7 protein stability was characterized under different light conditions. PRR7 degradation under white light, blue light, and darkness was similar during the subjective day and night. Under red light, the half-life of PRR7 protein was extended by almost an hour in the subjective evening as measured by Western blotting. PRR7 protein is stabilized by red light relative to darkness in the subjective evening. Blue light did not stabilize PRR7. ZTL does not affect PRR7 protein abundance; as blue light does not seem to affect PRR7 stability, it is unlikely that other members of the ZTL family regulate PRR7.
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