Kristen Edgeworth

Program: Plant and Microbial Biosciences

Current advisor: Dmitri A. Nusinow, PhD

Undergraduate university: Kenyon College, 2020

Enrollment year: 2020

Research summary
DGAT1, an important enzyme in triacylglycerol biosynthesis, is regulated by the circadian clock in plants. My focus is uncovering the mechanism and consequences of this regulation for daily rhythms in fat production.

Triacylglycerol (TAG) is a critical carbon storage lipid with important roles in promoting seed germination and mediating responses to many environmental stressors. The primary enzyme responsible for TAG biosynthesis is ACYL-COA:DIACYLGLYCEROL ACYLTRANSFERASE 1 (DGAT1). DGAT1 gene expression and the accumulation of TAG-containing oil bodies cycle diurnally in Arabidopsis seedlings. However, the mechanisms driving these daily rhythms and their significance for plant physiology remain understudied. DGAT1 expression continues to cycle, being most highly abundant in the evening, in seedlings grown under constant environmental conditions. This indicates that the circadian clock regulates DGAT1 expression in vegetative tissues. The circadian clock is an endogenous oscillator that controls the timing of many biological processes by regulating gene expression. Two important components of the circadian clock are CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY). CCA1 and LHY are partially redundant transcription factors that repress the expression of evening-phased circadian targets by binding to a common cis-regulatory motif. The DGAT1 promoter contains eight putative CCA1/LHY binding sites, two of which frame the transcriptional start site and would allow CCA1 and LHY to act together as a heterodimer. These two motifs are sufficient for both LHY interaction with the DGAT1 promoter in vitro and rhythmic DGAT1 expression. In cca1/lhy mutants, cyclic expression of DGAT1 is abolished and gene expression is significantly higher at dawn, suggesting that CCA1/LHY repress DGAT1 in the morning. Mutations in CCA1 and LHY also alter TAG levels in developing seeds. Together, this work provides preliminary evidence that the circadian clock directly regulates DGAT1 and potentially the timing of TAG production through CCA1 and LHY. If CCA1/LHY regulation of DGAT1 leads to daily TAG rhythms, this will be one of the first fully elucidated mechanisms demonstrating how specific circadian clock factors can directly regulate the production of a plant lipid metabolite.

Graduate publications