The Occurrence of Clock-Associated and Light-Induced PRR9 Pseudo-Response Regulator Protein in Arabidopsis Plants is Diurnally Oscillated and Subjected to Programmed-Degradation in the Dark

Abstract

In Arabidopsis thaliana, it is currently believed that the members of a small family of clock component PSUEDO-RESPONSE REGULATOR(PRR) proteins including TOC1 (PRR1) coordinately play crucial roles within the clock. Among them, the PRR9 gene is particuarly unique in that its expression is circadian-controlled and also rapidly induced by light at the level of transcription. Here we first dissected the regulatory cis-elements of the light-induced and/or circadian-controlled PRR9 promoter by employing a PRR9::LUC reporter. Nonetheless, these results did tell us nothing about the abundance of PRR9 protein product it self in plant. We then established a transgenic line expressing PRR9-TAP-tag polypeptides, by demonstrating that the occurrence of PRR9 polypeptides in plants is indeed diurnally oscillated. In addition, PRR9 polypeptides are accumulated rapidly in response to light. Interestingly, PRR9 polypeptides appear to be subjected to a proteasome-mediated programmed-degradation in the dark.