Discovery of Geranylgeranyl Pyrophosphate Synthase (GGPPS) Paralogs from _Haematococcus pluvialis_ Based on Iso-Seq Analysis and Their Function on Astaxanthin Biosynthesis  
[PERSON]  
1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China; [EMAIL_ADDRESS] (D.H.); [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (A.L.) [PERSON]  
1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China; [EMAIL_ADDRESS] (D.H.); [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (A.L.) [PERSON]  
1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China; [EMAIL_ADDRESS] (D.H.); [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (A.L.) [PERSON]  
1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China; [EMAIL_ADDRESS] (D.H.); [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (A.L.) [PERSON]  
1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China; [EMAIL_ADDRESS] (D.H.); [EMAIL_ADDRESS] (W.L. ); [EMAIL_ADDRESS] (A.L.) 1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China; dduhang@szu. As the most important source of natural astaxanthin, it is imperative to understand the biological process and the regulation of astaxanthin formation in _H. pluvialis_ aiming to improve the productivity of astaxanthin. The pathway of astaxanthin production in _H. pluvialis_ is complex but still has been described, which is originally started from pyruvate and glyceraldehyde-3-phosphate (GA-3P) followed by a series of enzymatic reactions [6; 7]. Briefly, isopentenyl diphosphate (IPP), the precursor of carotenoids, was synthesized through methyl-p-erythitol 4-phosphate (MEP) pathway using pyruvate, GA-3P, and enzymes of DXS and IspC-IspH [8; 9]. Subsequently, IPP and dimethylallyl diphosphate (DMAPP, an isomer of IPP that was formed by isopentenyl pyrophosphate isomerase (IPI) or 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR)), were used to form a C20 compound, geranylgeranyl pyrophosphate (GGPP), with the help of geranylgeranyl pyrophosphate synthase (GGPPS) [10; 11; 12; 13]. Carotenoids were then initialized using GGPP, in the main order of phytoene, \(\zeta\)-carotene, lycopene, \(\beta\)-carotene, cathaxanthin, and astaxanthin, with cooperation of enzymes of phytoenesystase (PSY), phytoenedesaturase (PDS), \(\zeta\)-carotenedesaturase (ZDS), lycopene \(\beta\)-cyclase (LCY-b), \(\beta\)-carotene ketolase (BKT), and \(\beta\)-carotene 3,3\({}^{\prime}\)-hydroxylase (CrrtR-b) [2; 7; 13]. Thereby, the GGPPS, a key enzyme defining the initial GGPP availability, is crucial for the subsequent flux of carotenoids biosynthesis, theoretically. It has been reported that the mechanism of the enzymatic reaction converting IPP to GGPP is conserved among organisms from bacteria to human [14; 15].