Abstract
Circadian clocks integrate environmental cues with endogenous signals to coordinate physiological outputs. Clock genes in plants are involved in many physiological and developmental processes, such as photosynthesis, stomata opening, stem elongation, light signaling, and floral induction. Many Brassicaceae family plants, including Chinese cabbage (Brassica rapa ssp. pekinensis), produce a unique glucosinolate (GSL) secondary metabolite, which enhances plant protection, facilitates the design of functional foods, and has potential medical applications (e.g., as antidiabetic and anticancer agents). The levels of GSLs change diurnally, suggesting a connection to the circadian clock system. We investigated whether circadian clock genes affect the biosynthesis of GSLs in Brassica rapa using RNAi-mediated suppressed transgenic Brassica rapa GIGENTEA homolog (BrGI knockdown; hereafter GK1) Chinese cabbage. GIGANTEA plays an important role in the plant circadian clock system and is related to various developmental and metabolic processes. Using a validated GK1 transgenic line, we performed RNA sequencing and high-performance liquid chromatography analyses. The transcript levels of many GSL pathway genes were significantly altered in GK1 transgenic plants. In addition, GSL contents were substantially reduced in GK1 transgenic plants. We report that the BrGI circadian clock gene is required for the biosynthesis of GSLs in Chinese cabbage plants.
Highlights
Organisms are exposed to daily environmental cycles of light and temperature
Multiple genes involved in secondary metabolite biosynthesis have diurnal expression patterns [16], and secondary metabolism alterations can influence the circadian clock [17]
We investigated the correlation between GI and biosynthesis of GSLs using transcriptomic tools and metabolic analysis
Summary
Organisms are exposed to daily environmental cycles of light and temperature. These. Arabidopsis thaliana oscillate cyclically as a function of light and/or temperature [6,7], regulating a variety of processes such as hypocotyl and root growth [8], flowering time [2], sugar metabolism [2], photosynthesis [9], nutrient homeostasis [10], and hormonal signaling [11]. Multiple genes involved in secondary metabolite biosynthesis have diurnal expression patterns [16], and secondary metabolism alterations can influence the circadian clock [17]. Genetic perturbations in the GSL pathway can influence the transcript abundance of core oscillator genes [6], while GSL genotypes altered the periodicity of a clock output unrelated to GSLs, i.e., the photochemical state of photosystem II This suggests that the GSL pathway in plants is not related to carbon/nitrogen/sulfur flux, and to growth-defense tradeoffs via circadian clock regulation [17]. Our results suggest that manipulating the clock gene expression could improve the productivity and functionality of crops
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