Linkage between circadian clock and tricarboxylic acid cycle in Arabidopsis.

The transcriptional/translational feedback loop is thought to play a central role in the circadian clock in Arabidopsis. The loop includes close paralogs of MYB transcription factors CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), TIMING OF CAB EXPRESSION 1 (TOC1, PSEUDO RESPONSE REGULATOR 1[PRR1]), PRR9, PRR7 and PRR5. The prr9 prr7 prr5 triple mutants (d975) and overexpression line of CCA1 (CCA1-ox) are arrhythmic under continuous light conditions followed by light and dark cycles. We recently demonstrated a tight link between the circadian clock and the tricarboxylic acid (TCA) cycle, from the metabolome analysis of d975. The levels of metabolites belonging to TCA cycle, such as 2-oxoglutarate, succinate, fumarate, citrate and malate increased in d975, whereas those of arginine and ornithine decreased. In this addendum, we further demonstrate that metabolism belonging to TCA cycle in CCA1-ox was partly similar to that of d975. This profiling also supported the linkage between circadian clock and metabolism associated to TCA cycle.