The transcripts annotated in+N and — N transcriptomes were first clas­sified based on Gene Ontology (GO) terms. In the+N and — N datasets, respectively, 6,846 and 7,473 transcripts were classified into 306 and 218 broader GO term categories in accordance with the Gene Ontology Consortium [26]. An enrichment analysis of the broader GO terms was performed using the modified Fisher’s Exact test in Blast2GO to quanti­tatively compare the distribution of differentially enriched GO terms be­tween the+N case and the entire data set (Figure 4A), and between the — N case and the entire data set (Figure 4B). The functional categories enriched under+N were distinctly different from those enriched under the — N condition. In the+N case (Figure 4A), functional categories linked to carbon fixation, photosynthesis, protein machinery, and cellular growth were highly enriched compared to the — N condition; reflecting the higher growth rate, higher cell mass, and increased chlorophyll content observed in+N. Under — N conditions, genes associated with carboxylic acid and lipid biosynthetic process, NADPH regeneration, the pentose-phosphate pathway, phospholipid metabolic process, and lipid transport demonstrat­ed a greater enrichment of transcripts than the overall dataset (Figure 4B). These enriched GO terms directly correlated with the observed increase of lipid accumulation in — N cells. Other major categories identified as significantly expressed under the -N condition included the synthesis of value added products such as terpenoids, pigments, and vitamins as well as cellular response to nitrogen starvation, nitrate metabolic process, and nitrate assimilation (Figure 4B). Genes involved in the latter three func­tional categories were exclusively expressed in the nitrogen-limited cells.