Dependence and independence of the root clock on the shoot clock in Arabidopsis.

Temporal and spatial compartmentalization of biological processes is facilitated by tissue-specific uncoupled circadian clocks in plants. However, interactions among tissue-specific circadian clocks have not been well established. The primary objective of this study was to describe both organ-specific circadian behaviors and centralized actions of the root clock. We analyzed transcript accumulation of circadianly-oscillating genes in roots and shoots. Expression of many clock components was different in roots and shoots. In particular, evening-expressed clock components were highly expressed in roots and likely play important roles in oscillation of the root clock. Consistent with this, the root and shoot clocks responded differentially to circadian gene mutations. The root clock was even dampened in gi-2 mutant. Circadian clocks basically oscillate in an organ-specific manner in plants, but the root clock also requires shoot-derived signals for organism-level coordination of circadian activity.