Microarray analysis of diurnal and circadian-regulated genes in Arabidopsis

Plants respond to day/night cycling in a number of physiological ways. At t he mRNA level, the expression of some genes changes during the 24-hr period . To identify novel genes regulated in this way, we used microarrays contai ning 11,521 Arabidopsis expressed sequence tags, representing an estimated 7800 unique genes, to determine gene expression levels at 6-hr intervals th roughout the day. Eleven percent of the genes, encompassing genes expressed at both high and low levels, showed a diurnal expression pattern. Approxim ately 2% cycled with a circadian rhythm. By clustering microarray data from 47 additional nonrelated experiments, we identified groups of genes regula ted only by the circadian clock. These groups contained the already charact erized clock-associated genes LHY, CCA1, and Gl, suggesting that other key circadian clock genes might be found within these clusters.