Red Light Control of β-Carotene Isomerisation to 9-cis β-Carotene and Carotenoid Accumulation in Dunaliella salina

Abstract

Dunaliella salina is a rich source of 9-cis β-carotene, which has been identified as an important biomolecule in the treatment of retinal dystrophies and other diseases. We previously showed that chlorophyll absorption of red light photons in D. salina is coupled with oxygen reduction and phytoene desaturation, and that it increases the pool size of β-carotene. Here, we show for the first time that growth under red light also controls the conversion of extant all-trans β-carotene to 9-cis β-carotene by β-carotene isomerases. Cells illuminated with red light from a light emitting diode (LED) during cultivation contained a higher 9-cis β-carotene content compared to cells illuminated with white or blue LED light. The 9-cis/all-trans β-carotene ratio in red light treated cultures reached >2.5 within 48 h, and was independent of light intensity. Illumination using red light filters that eliminated blue wavelength light also increased the 9-cis/all-trans β-carotene ratio. With norflurazon, a phytoene desaturase inhibitor which blocked downstream biosynthesis of β-carotene, extant all-trans β-carotene was converted to 9-cis β-carotene during growth with red light and the 9-cis/all-trans β-carotene ratio was ~2. With blue light under the same conditions, 9-cis β-carotene was likely destroyed at a greater rate than all-trans β-carotene (9-cis/all-trans ratio 0.5). Red light perception by the red light photoreceptor, phytochrome, may increase the pool size of anti-oxidant, specifically 9-cis β-carotene, both by upregulating phytoene synthase to increase the rate of biosynthesis of β-carotene and to reduce the rate of formation of reactive oxygen species (ROS), and by upregulating β-carotene isomerases to convert extant all-trans β-carotene to 9-cis β-carotene.

Stereoisomers of Colourless Carotenoids from the Marine Microalga Dunaliella salina

“…Our results show that 15-cis phytoene is the main stereoisomer produced by D. salina and that it is over-accumulated with red light and with the use of herbicides. Our results also support the recent finding that 9-cis β-carotene is formed by isomerisation of all-trans β-carotene with the function of a 9-cis/all-trans β-carotene isomerase [19,20], rather than synthesised from the precursor of 9-cis phytoene.…”

“…Ebenezer [18] for example showed by using Nuclear Magnetic Resonance (NMR) methods that the main phytoene isomer, which accumulated in norflurazon-treated D. bardawil cultures (Dunaliella bardawil is a variant of Dunaliella salina), was the 15-cis isomer, whilst Werman et al [6] and Ben-Amotz et al [13] using High Performance Liquid Chromatography (HPLC) techniques, reported that the phytoene-rich D. bardawil powder used in their study contained the 9-cis phytoene isomer together with all-trans phytoene. This leads to an unresolved point in regard to the carotenoid biosynthetic pathway of D. salina: whether the high quantity of 9-cis β-carotene derives directly from 9-cis phytoene, as proposed in [13], or from the isomerization of all-trans β-carotene, as proposed by Davidi et al [19] and by Xu and Harvey [14,20]. Resolving the identity of the phytoene isomers produced by D. salina could provide new insight into the carotenoid synthesis pathway and clarify this point.…”

CRISPR/Cas9-induced β-carotene Hydroxylase Mutation in Dunaliella Salina CCAP19/18

“…Subsequently, gene expression level was calculated by 2 −∆∆Ct method with ABI 7500 manager program. On the other hand, biomass was harvested and extracted for high-performance liquid chromatography (HPLC) analysis as described by Xu et al with slight modi cation (Xu et al 2019).…”

“…Although several studies have addressed the effect of different culture conditions on β-carotene content in D. salina, its accumulation leads to reduced growth rates, including extreme temperatures, high salinity, and nitrogen limitation (Xu et al 2019). So, molecular approaches have shown great potentials to enhance the accumulation of bio-products, such as metabolic engineering, transcriptional engineering, and gene disruption strategies (Wichuk et al 2014;Zhang et al 2018).…”

Marine Algal Antioxidants

“…Dunaliella salina, a chlorophyte that is mostly used for biotechnological investigations and applications, mainly relies on the production of β-carotene [9], has been used as a model to study the modulation of carotenoids and β-carotene concentration with respect to the light spectrum [10,11]. This study demonstrates that monochromatic red light strongly affects the carotenoid pool, enhancing the β-carotene concentration as well as modifying the ratio between the different forms of β-carotene towards 9-cis β-carotene.…”