Circadian clock factors regulate seed oil accumulation by promoting fatty acid synthesis in Arabidopsis

Abstract

The circadian clock regulates temporal metabolic activities, enabling organisms to adapt to cyclic environmental changes, but how it affects lipid metabolism in plants is poorly understood. Our previous finding showed that the central clock transcription factors LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) increased seed oil contents. Here we investigated the molecular and metabolic mechanism underlying the LHY and CCA1 regulated oil accumulation. Triacylglycerol (TAG) accumulation in Arabidopsis developing seeds increased in LHY-overexpressing (LHY-OE) and decreased in lhycca1 plants compared to wild-type (WT). Metabolic tracking indicated that fatty acids (FAs) of major lipid precursors for TAG production increased more rapidly in LHY-OE and slowly in lhycca1 than in WT, suggesting that LHY enhanced FA synthesis. Transcript analysis revealed that the expression of genes involved in FA synthesis, including beta-ketoacyl-ACP synthase III (KASIII), was oppositely changed in developing seeds of LHY/CCA1-OEs and lhycca1. Chromatin immunoprecipitation, electrophoretic mobility shift, and transactivation assays indicated that LHY directly bound and activated the promoter of KASIII. Furthermore, phosphatidic acid, a metabolic precursor to TAG, inhibited LHY binding to KASIII promoter elements. Our data reveal a new regulatory mechanism by the core clock regulators for storage lipid production during plant seed development.

Identification of phospholipase Ds and phospholipid species involved in circadian clock alterations using CRISPR/Cas9-based multiplex editing of Arabidopsis

“…The interplay between the clock and metabolism is expected to strengthen the function of both processes in organisms. Increasing evidence supports the clock regulation of plant lipid metabolism, including the recent findings that the core Arabidopsis clock morning regulators LHY/CCA1 enhance fatty acid biosynthesis and lipid accumulation (Kim et al, 2019, 2023). In contrast, the evening regulator TOC1 decreases lipid production (Makni et al, 2024).…”

“…Reciprocally, the circadian clock modulates lipid metabolism by regulating the expression of lipid metabolic genes, as evidenced by circadian profiles of the genes and oscillatory accumulation of some lipid metabolites, including PA, in plants (Maatta et al, 2012; Hsiao et al, 2014; Nakamura et al, 2014 a and b; Kim et al, 2019). Recently, we reported that LHY and CCA1 enhanced the expression of KASIII that encodes β-ketoacyl-ACP synthase III by directly binding to its promoter, and this binding was inhibited by PA (Kim et al, 2023). KASIII catalyzes the first condensation step in the biosynthetic pathway of fatty acids incorporated into myriad lipid species.…”

“…We also found that cellular PA abundance directly correlated with the period of circadian rhythms, such as the vertical movement of plant leaves and the oscillatory expression of the LHY/CCA1 target TIMING OF CAB EXPRESSION1 ( TOC1 ) (Kim et al, 2019). In addition, our recent results indicate that the PA-clock interaction attenuates the LHY/CCA1 promotion of fatty synthesis and storage lipid accumulation (Kim et al, 2023). These findings suggest that PA is a vital regulator of the plant circadian clock.…”

Unveiling the Impact of Vernalization on Seed Oil Content and Fatty Acid Composition in Rapeseed Through Simulated Shorter Winters

“…Understanding seed development as a complex mechanism involving intricate pathways implies that multiple factors may contribute to the formation of seed components. A recent study unraveled the direct role of circadian rhythm regulators in initiating fatty acid synthesis in Arabidopsis seeds (Kim et al, 2023), further underscoring the multifaceted nature of seed development.…”