EXORIBONUCLEASE4 integrates metabolic signals induced by osmotic stress into the circadian system

The circadian clock system acts as an endogenous timing reference that coordinates many metabolic and physiological processes in plants. Previous studies have shown that the application of osmotic stress delays circadian rhythms via 3’-Phospho-Adenosine 5’-Phosphate (PAP), a retrograde signalling metabolite that is produced in response to redox stress within organelles. PAP accumulation leads to the inhibition of EXORIBONUCLEASEs (XRNs), which are responsible for RNA degradation. Interestingly, we are now able to demonstrate that post-transcriptional processing is crucial for the circadian response to osmotic stress. Our data show that degradation of specific circadian clock transcripts is modulated by osmotic stress, suggesting that RNA metabolism plays a vital role in circadian clock coordination during drought. Inactivation of XRN4 is sufficient to extend circadian rhythms, with LWD1, LWD2 , and PRR7 identified as specific XRN4 targets that are post-transcriptionally regulated to delay circadian progression. One Sentence Summary Post-transcriptional regulation of specific transcripts enables the circadian system to respond to osmotic stress.