TOC1 and PRR5 as regulators of temperature compensation in the Arabidopsis circadian clock (17˚C vs 27˚C)

Ambient temperature potentially affects all biological systems. However, the period length of circadian clocks is close to 24 h over a broad range of physiological temperatures, known as temperature compensation. The mechanism underpinning the temperature compensation remains largely unknown. Here, we show that inhibitors of time progression, TIMING OF CAB EXPRESSION 1 (TOC1) and PSEUDO-RESPONSE REGULATOR 5 (PRR5) proteins, are required for the temperature compensation in Arabidopsis thaliana (Arabidopsis). Compared to the wild-type, the prr5 toc1 double mutant shows a short period at high temperatures but not low temperatures. TOC1 and PRR5 proteins are ubiquitinated and degraded at low temperatures, by a ubiquitin E3 ligase LOV KELCH PROTEIN 2 (LKP2) that was sought as a minor player in the clock. The lkp2 mutants show long periods only at lower temperatures. Collectively, the clock keeps its periodicity against ambient temperature by the temperature-dependent quantity control of inhibitors of time progression.