Rhythmic growth explained by coincidence between internal and external cues

Plant hypocotyls elongate in response to darkness. The response to darkness is gated by the circadian clock, such that wild-type plants (Col) only respond to darkness with growth once every 24 hours, whereas arrhythmic lines, such as CCA1-34, will respond to darkness with growth at any time of day. The experiment here was designed to find genes whose expression was correlated with growth. It should also pick up other genes that are gated by the circadian clock or that are direct targets of CCA1. Keywords: time course Two genotypes were uses, wild-type (Col) and the arrhythmic CCA1-34 line that overexpresses the CCA1 protein. Plants were entrained in short day conditions for four days and then subjected light/dark pulses consisting of 160 minutes of light and 320 minutes of dark. We collected samples 120 minutes into the first and last dark periods of the day, corresponding to 280 and 1240 minutes after dawn. At the 280 minute time point Col plants are growing in response to darkness. At the 1240 minute time point Col plants are not growing. CCA1-34 plants are growing at both time points. The collection regime was continued for three days for a total of three temporal replicates for each time point/genotype combination.