A bZIP transcription factor is involved in regulating lipid and pigment metabolisms in the green alga Chlamydomonas reinhardtii

Roles of bZIP transcription factors in microalgae remain poorly understood. Here we comparatively dissected crbzip2, a Chlamydomonas reinhardtii mutant defective in CrbZIP2, and wild-type (WT) strain by integrated analysis of physiological, biochemical and transcriptomic data. CrbZIP2, up-regulated by nitrogen deprivation, was severely impaired at the transcriptional level in crbzip2 as compared to WT. CrbZIP2 disruption attenuated triacylglycerol (TAG) accumulation yet promoted polar lipids particularly digalactosyl diacylglycerol (DGDG). Furthermore, CrbZIP2 disruption allowed the alga to synthesize more carotenoids and chlorophylls. TAG attenuation and DGDG enhancement are probably attributed to transcriptionally up-regulated TAG catabolism and down-regulated DGDG degradation, respectively. By contrast, increases of carotenoids and chlorophylls are likely due to up-regulation of their biosynthetic pathways. Our results shed light on multiple roles of CrbZIP2 as a hub in regulating lipid and pigment metabolisms in C. reinhardtii and suggest that it may serve as a gene target for genetic engineering purposes.