Chloroplast morphogenesis in Chromochloris zofingiensis in the dark

Abstract In the present study, chloroplasts were found to form after glucose was consumed in Chromochloris zofingiensis under heterotrophic cultivation, accompanied by a significant increase in chlorophyll and primary carotenoids. These changes conferred photosynthetic ability to heterotrophic cells. Meanwhile, both fatty acid and starch were catabolized to provide carbon and energy for cellular metabolism. A comparative transcriptome analysis showed that the expression of genes encoding photosynthetic proteins, as well as enzymes involved in chlorophyll and carotenoid biosynthesis were significantly up-regulated after glucose was consumed. At the same time, genes involved in fatty acid and starch biosynthesis were down-regulated, while those involved in the degradation of these storage molecules were up-regulated. Further investigation by means of enrichment analysis and gene co-expression network analysis revealed that the cells may control the above intracellular changes by directly regulating the expression levels of constitutively photomorphogenic 1, related transcription factors and the peroxisome proliferator-activated receptor signaling pathway. This work, for the first time, highlights the phenomenon of chloroplast morphogenesis in Chromochloris zofingiensis under dark conditions, and suggests possible regulatory mechanisms.