Characterizing Circadian Response to Cold Stress in Diverse Arabidopsis thaliana Ecotypes
The circadian clock, a 24-hour oscillator present in all kingdoms of life, coordinates physiological changes with respect to the time of day and surrounding environmental signals, such as light and temperature. Defined by a set of transcriptional-translational feedback loops that generate time of day gene expression, the circadian clock regulates genes involved in abiotic stress response such as freeze stress. To harness the benefits of the circadian clock, the genetic attributes related to enhanced stress tolerance must first be identified. Previously, we screened ten geographically-diverse ecotypes of Arabidopsis thaliana for relative freeze stress tolerance. In this study, the circadian rhythms, defined by period length, of each of the ten ecotypes was measured through leaf movement in cold (10º C) and control (22º C) conditions. The control condition plants were grown for seven days in 14:10 light:dark light cycle before being switched into the constant light and constant 22º C. The cold condition plants were grown for seven days in the same conditions, and were given an additional 3-day cold acclimation period with 14:10 LD light cycling and 10º C: 4º C temperature cycling before transitioning to constant light and constant 10º C. To obtain the circadian rhythm through leaf movement, the plants were photographed every 20 minutes for five days after being moved to constant light conditions.The circadian responses to cold present in genotypes with enhanced freeze tolerance were identified by comparing the shifts in circadian rhythms due to the cold stress between the previously determined cold-tolerant and cold-sensitive ecotypes.