Analysis of the function of two circadian-regulated CONSTANS-LIKE genes

The Arabidopsis genes CONSTANS-LIKE 1 (COL1) and CONSTANS-LIKE 2 (COL2) are predicted to encode zinc finger proteins with similar to 67% amino acid id entity to the protein encoded by the flowering-time gene CONSTANS (CO). We show that the circadian clock regulates expression of COL1 and COL2 with a peak in transcript levels around dawn. We analyzed transgenic plants misexp ressing COL1, COL2 and CO. Unlike CO, altered expression of COL1 and COL2 i n transgenic plants had little effect on flowering time. However, analysis of circadian phenotypes in the transgenic plants showed that over-expressio n of COL1 can shorten the period of two distinct circadian rhythms. Experim ents with the highest COL1 overexpressing line indicate that its circadian defects are fluence rate-dependent, suggesting an effect on a light input p athway(s).