Molecular investigation of organ‐autonomous expression of Arabidopsis circadian oscillators.

The circadian pacemaker in plants is a hierarchical multioscillator system that directs and maintains a 24‐hr oscillation required for organism homeostasis and environmental fitness. Molecular clockwork within individual tissues and organs acts cell autonomously, showing differences in circadian expression of core oscillators and their target genes; there are functional dominance and coupling in the complex regulatory network. However, molecular characteristics of organ‐specific clocks are still unknown. Here, we showed the detached shoot and root possess dynamic circadian protein–protein interactions between clock core components, periodicity in organs exhibits a difference. The period length difference between shoot and root was not remarkable in prr7‐3 and prr7‐3 prr9‐1 mutants. In addition, the phase transition curve indicated that shoot and root clock respond differently to the resetting cues of ambient temperature. PRR9 and PRR7 compensate circadian period between 22°C and 28°C in shoot, not in root. The circadian rhythms of PRR9 or PRR7 transcript accumulation showed no difference at 22°C and 28°C in shoot, but differences were observed in root. In summary, our results reveal the specificity of dynamic circadian protein–protein interactions in organ‐autonomous clocks and the critical roles of PRR9 and PRR7 in mechanisms regulating temperature compensation in aerial shoot system. We found the difference of circadian period length of dynamic circadian protein–protein interactions between shoot and root. PRR9 and PRR7 were found to contribute significantly to organ‐specific circadian periodicity maintenance and in the temperature compensation of aerial shoot clock. To the best of our knowledge, this is the first example in plants monitoring clock protein interactions in real time in individual organs. Having demonstrated the uniqueness and consistency of clock components function in aerial shoot and subterranean root, we are able to pose a variety of intriguing questions about the adaptive evolution and hierarchical coupling in the plant clock system. [ABSTRACT FROM AUTHOR]