Red light promotes autotrophic growth of Haematococcus pluvialis with improved carbonic anhydrase activity and CO2 utilization

This study focused on the green vegetative growth stage of Haematococcus pluvialis (H. pluvialis), investigating the effect of red light on carbon dioxide utilization and biomass accumulation of algal cells. Under the proper conditions of photosynthetic autotrophy, the biomass could be increased by about 50% after switching from white light to red light. Interestingly, it was found that red light could promote the algal cells into higher photosystem II (PSII) activity increasing the gene expressions of carbonic anhydrases (CAH1 and CAH3), Myb transcription factor LCR1 (Lcr1), and Rubisco (rbcL) proteins. Further investigation revealed that the genes related to photoreceptor interaction factors (COP1, SPA1) and photosynthetic light capture protein (LHCA2) were also up-regulated, suggesting that red light promoted carbonic anhydrase (CA) activity by regulating the COP1/SPA1 complex to maintain the pH stability and enhance the photosynthetic carbon fixation rate.