Transcriptome-wide analysis of nitrate starvation in Messastrum gracile: Impact on nitrogen and carbon metabolism

Duration of nitrate starvation exposure induces changes in microalgal nitrogen and carbon metabolism. However, molecular nitrogen and carbon metabolism adjustments remain unclear during nitrate starvation, especially in the non-model chlorophyte microalga, Messastrum gracile SE-MC4. Transcriptome analysis successfully identified 10 and 16 genes significantly affected concerning nitrogen and carbon metabolism, respectively. A short exposure period to nitrate starvation triggered the up-regulation of nitrogen metabolism-related genes. In contrast, a prolonged exposure period to nitrate starvation up-regulated carbon metabolism-related genes. Therefore, a short period of exposure to nitrate starvation was characterized by an increased need to secure nitrogen sources. In contrast, prolonged exposure to nitrate starvation displaces energy metabolism from the plastid to the mitochondria via increased TCA activity. The findings illustrate the stress regulation and defense strategies activated during nitrate starvation.