2018 年 83 巻 1 号 p. 7-17
In order to increase the biomass of photosynthetic organisms, upregulation of net CO2 fixation in daytime appears to be a promising approach. This can be attained by improving the turnover of chloroplast enzymes such as ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) or fructose bisphosphate phosphatase (FBPase). In a previous report, the genes for the large and small subunits of cyanobacterial Rubisco were coexpressed in tobacco with either with cyanobacterial chaperone for Rubisco or the carboxysomal CO2 concentrating mechanism (CCM) gene. This resulted in the generation of faster carboxylation of Rubisco and a similar gene expression approach may be adopted into algal hosts in the future. Expression of the cyanobacterial FBPase gene with protein targeting to the chloroplast in Euglena gracilis was reported to increase the wax ester content effectively. Though stable transformation of the oil producing alga Botryococcus braunii race B, is yet to be achieved, genes for key regulatory enzymes in 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, such as 1-deoxy-D-xylulose 5-phosphate synthase (DXS) or 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR), might be possible targets for genetic modification in this alga. Challenging problems in the transformation of the microalgae, including C. reinhardtii, or those of the macroalgae are discussed herein for the design of transformation aiming at higher yield of biofuel production.
