Circadian clocks play important roles in regulating cellular metabolism， but the reciprocal effect that metabolism has on the clock is largely unknown in plants. Here， we show that the central glycerolipid metabolite and lipid mediator phosphatidic acid (PA) interacts with and modulates the function of the core clock regulators LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED1 (CCA1) in Arabidopsis (). PA reduced the ability of LHY and CCA1 to bind the promoter of their target gene Increased PA accumulation and inhibition of PA-producing enzymes had opposite effects on circadian clock outputs. Diurnal change in levels of several membrane phospholipid species， including PA， observed in wild type was lost in the and double knockout mutant. Storage lipid accumulation was also affected in the clock mutants. These results indicate that the interaction of PA with the clock regulator may function as a cellular conduit to integrate the circadian clock with lipid metabolism.