Plants measure the time

All eukaryotes, including plants, and most prokaryotes have developed elaborate mechanisms to anticipate external environmental changes associated with the Earth’s rotation. These mechanisms are mediated by a circadian clock, which regulates several physiological and biochemical processes. Microarray experiments using Affymetrix chips that included about 8000 of the 27000 Arabidopsis genes have demonstrated that as much as 6% of that genome may be under the control of this clock. While our understanding of such mechanisms is lagging, molecular genetics studies of Arabidopsis have allowed us to make great progress toward identifying and characterizing components of the plant circadian clock since its first component was isolated in 1995. The generation of 24-h rhythms by this clock appears to rely on mechanisms similar to those found in other organisms. However, an entirely different set of molecular components are recruited to perform these functions in Arabidopsis. In this review, we introduce useful and powerful approaches for identifying clock-associated genes and determining how they can act together in the interlocking feedback loops that comprise this particular clock.