the target genes are unknown. During Q2, one transcription factor had decreased expression while all others had increased expression (2-fold to 48-fold; p &lt;?0.05). During extended stationary-phase and lipid accumulation (Q3), 4 transcription factors had decreased expression and 20 transcription factors had increased expression (2-fold to 11-fold; p &lt;?0.05). This also correlates to the cyclin expression and diatom specific cyclin (dsCYC) expression results. It has been proposed by Huysman et al . 2010 [ 36 ] that dsCYCs may act as signal integrators for a fluctuating environment ( e . g ., changes in light intensity, temperature, and nutrient availability). The Huysman et al. study reported that ds cyc7 and ds cyc10 were indicators of phosphate availability and that gene expression increased with increased phosphate availability. In our results, both ds cyc 7 and ds cyc 10 had increased expression (17-fold and 7-fold, respectively; p &lt;?0.05) during Q2 when phosphate was internally available and most likely stored as polyphosphate. During Q3, ds cyc7 and ds cyc10 decreased in transcript abundance by 85% and 49% respectively, and coincided with the phosphate stress during Q3. Conserved cyclin ( cyc B1) is a late-phase cell cycle (G2/M) gene that shows a slight decrease in abundance in Q2 and a nearly 4-fold increase in transcript abundance during Q3 compared to Q1. The increased expression of cyc B1 suggests a role during cell-cycle arrest induced by nutrient deprivation of both nitrogen and phosphorus. Nitrogen-limitation response Genes involved in nitrogen metabolism were highly up-expressed at Q2