HSP90 Contributes to Entrainment of the Circadian Clock via the Morning Loop.

The plant circadian clock allows the synchronization of internal physiological responses to match the predicted environment. HSP90.2 is a molecular chaperone that has been previously described as required for the proper functioning of the oscillator under both ambient and warm temperatures. Here, we have characterized the circadian phenotype of the mutant. As previously reported using pharmacological or RNA interference inhibitors of HSP90 function, we found that lengthens the circadian period and that the observed period lengthening was more exaggerated in warm-cold-entrained seedlings. However, we observed no role for the previously identified interactors of HSP90.2, GIGANTEA and ZEITLUPPE, in -mediated period lengthening. We constructed phase-response curves (PRCs) in response to warmth pulses to identify the entry point of HSP90.2 to the oscillator. These PRCs revealed that has a circadian defect within the morning. Analysis of the , , , and mutants revealed a role for CCA1, LHY, and PRR7, but not PRR9, in HSP90.2 action to the circadian oscillator. Overall, we define a potential pathway for how HSP90.2 can entrain the circadian oscillator.