Fig. 4.

C. zofingiensis astaxanthin-deficient mutants. Astaxanthin-deficient mutants were generated by using forward genetics; mutations were identified in BKT1. (A) HPLC traces of wild type, bkt1-1, bkt1-2, and bkt1-3 grown under high light (HL, 400–450 μmol photons⋅m⁻²⋅s⁻¹), showing the mutants’ lack of astaxanthin production. Pigment abbreviations are as follows: A (antheraxanthin), α (α-carotene), Ast (astaxanthin), β (β-carotene), Chl a (chlorophyll a), Chl b (chlorophyll b), L (lutein), N (neoxanthin), V (violaxanthin), Z (zeaxanthin). Pigments were detected at 445 nm with reference at 550 nm (SI Appendix, SI Text). Inset shows high light WT growth with astaxanthin resulting in orange-brown color from astaxanthin (orange) and chlorophylls (green), whereas mutants bkt1-1, bkt1-2, and bkt1-3 do not produce astaxanthin and remain green. Under medium light (ML, 100 μmol photons⋅m⁻²⋅s⁻¹), WT does not produce high amounts of astaxanthin and remains green with similar color as bkt1-1, bkt1-2, and bkt1-3. (B) Pigment levels (mean ± SD, n = 3 or 4) in HL-grown WT, bkt1-1, bkt1-2, and bkt1-3 showing higher levels of carotenoids with similar levels of chlorophyll. *P < 0.05, **P < 0.01, ***P < 0.001 (SI Appendix, SI Text).