Time of day shapes the Arabidopsis drought transcriptomes

Under natural conditions, plants experience episodes of drought for periods of days or longer. Plants respond to drought stress by reconfiguring their transcriptome activity. Transcriptome changes in response to drought are dynamic, and are likely to be shaped by mitigating factors such as diel signals. To gain insights into the dynamics of transcriptome reconfiguration in response to gradual soil drying, the drought-induced transcriptomes of Arabidopsis thaliana were examined at four time points over a single diel period – midday, late day, midnight, and pre-dawn. A core set of genes was identified that was responsive to drought, independent of the time of day at which they were measured. Strikingly, the magnitude of the drought-induced changes for these genes varied in a time-of-day-dependent manner. An additional set of time-of-day-specific drought-responsive genes were also identified. The diurnal patterns of transcript accumulation for these genes was strongly influenced by drought stress. This study indicates that analysis of a single time point would miss suites of drought-responsive genes that are revealed through assessment of the dynamics of diurnal changes, emphasizing the value of characterizing multiple time-of-day-specific drought transcriptomes. 24 arrays total. 4 time points (midday, late day, midnight, pre-dawn). 2 water regimes (well-watered, water-limited). 3 biological replicates per treatment.