The Loroxanthin Cycle: A New Type of Xanthophyll Cycle in Green Algae (Chlorophyta)

Abstract

Xanthophyll cycles (XC) have proven to be major contributors to photoacclimation for many organisms. This work describes a light-driven XC operating in the chlorophyte Chlamydomonas reinhardtii and involving the xanthophylls Lutein (L) and Loroxanthin (Lo). Pigments were quantified during a switch from high to low light (LL) and at different time points from cells grown in Day/Night cycle. Trimeric LHCII was purified from cells acclimated to high or LL and their pigment content and spectroscopic properties were characterized. The Lo/(L + Lo) ratio in the cells varies by a factor of 10 between cells grown in low or high light (HL) leading to a change in the Lo/(L + Lo) ratio in trimeric LHCII from .5 in low light to .07 in HL. Trimeric LhcbMs binding Loroxanthin have 5 ± 1% higher excitation energy (EE) transfer (EET) from carotenoid to Chlorophyll as well as higher thermo- and photostability than trimeric LhcbMs that only bind Lutein. The Loroxanthin cycle operates on long time scales (hours to days) and likely evolved as a shade adaptation. It has many similarities with the Lutein-epoxide – Lutein cycle (LLx) of plants.

Seasonal Monitoring of Volatiles and Antioxidant Activity of Brown Alga Cladostephus spongiosus

“…El Hattab et al [57] reported fucoxanthin in C. spongiosus f. verticillatus. Halocynthiaxanthin acetate and loroxanthin decenoate are more abundant in green algae [58]. Xanthophylls exhibit diverse bioactive properties, such as antioxidant, antitumor, and anti-inflammatory activities [55,56,59].…”

CRISPR/Cas9-Mediated Knockout of the Lycopene ε-Cyclase for Efficient Astaxanthin Production in the Green Microalga Chlamydomonas reinhardtii

“…In C. reinhardtii, α-carotene is hydroxylated by the activity of P450 ε/ß-ring hydroxylases (CYP97A and CYP97C) [9] at both C3 positions for the synthesis of lutein, a common, yellow-red colored xanthophyll found in all green plants and their progenitors. The native cellular abundance in C. reinhardtii varies depending on the present light intensity [10], is reported to range between 1.77 and 4.13 mg/g [11][12][13], and was engineered to 8.9 mg/g [12] by the overexpression of Xanthophyllomyces dendrorhous phytoene-β-carotene synthase (crtYB). An alternative strategy, by the overexpression of C. reinhardtii LCYE, resulted in a 2.6-fold increased lutein production (to 0.48 mg/L) [14].…”

“…An alternative strategy, by the overexpression of C. reinhardtii LCYE, resulted in a 2.6-fold increased lutein production (to 0.48 mg/L) [14]. Lutein can be further hydroxylated at the C9 position to form loroxanthin by a yet unknown enzyme [15], and the lutein-loroxanthin cycle has a potential function in non-photochemical quenching (NPQ) [10,[16][17][18].…”