TCP transcription factors link the regulation of genes encoding mitochondrial proteins with the circadian clock in Arabidopsis thaliana.

Diurnal regulation of transcripts encoding proteins located in mitochondria, plastids, and peroxisomes is important for adaptation of organelle biogenesis and metabolism to meet cellular requirements. We show this regulation is related to diurnal changes in promoter activities and the presence of specific cis-acting regulatory elements in the proximal promoter region [TGGGC(C/T)], previously defined as site II elements, and leads to diurnal changes in organelle protein abundances. These site II elements can act both as activators or repressors of transcription, depending on the night/day period and on the number and arrangement of site II elements in the promoter tested. These elements bind to the TCP family of transcriptions factors in Arabidopsis thaliana, which nearly all display distinct diurnal patterns of cycling transcript abundance. TCP2, TCP3, TCP11, and TCP15 were found to interact with different components of the core circadian clock in both yeast two-hybrid and direct protein-protein interaction assays, and tcp11 and tcp15 mutant plants showed altered transcript profiles for a number of core clock components, including LATE ELONGATED HYPOCOTYL1 and PSEUDO RESPONSE REGULATOR5. Thus, site II elements in the promoter regions of genes encoding mitochondrial, plastid, and peroxisomal proteins provide a direct mechanism for the coordination of expression for genes involved in a variety of organellar functions, including energy metabolism, with the time-of-day specific needs of the organism.

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