Comparative transcriptome study highlights the versatility of nitrogen metabolism in Chlamydomonas

Abstract

Nitrogen is an essential macronutrient and nitrate is one of the main forms of this macronutrient available for plants and microbes. Nitrate is not only the substrate for the nitrate assimilation pathway, but also a crucial signal for the regulation of numerous metabolic, developmental, and cellular differentiation processes. In the present study, two species of the Chlamydomonas genus, Chlamydomonas reinhardtii cc124 and Chlamydomonas sp. MACC-216 were used to investigate the versatility of nitrate metabolism in green microalgae. Quantification of nitrate removal efficiency showed that Chlamydomonas sp. MACC-216 strongly outperforms C. reinhardtii cc124. Transcriptional changes occurring under nitrate-replete and nitrate-deplete conditions were specifically investigated in the selected species of Chlamydomonas. Whole transcriptome analysis revealed that the genes playing a role in nitrate assimilation did not show differential expression in C. reinhardtii cc124 under changing nitrate conditions (only 45 genes exhibited differential regulation), while in Chlamydomonas sp. MACC-216 a large set of genes (3143) showed altered expression. Furthermore, genes responsible for urea metabolism, like DUR3A gene corresponding to urea transport, were found to be upregulated in Chlamydomonas sp. MACC-216 under nitrate-deplete condition, while the same gene showed elevated expression level in C. reinhardtii cc124 under nitrate-replete condition. The present study indicated the diverseness of nitrate metabolism among species within the Chlamydomonas genus.