DescriptionDiatoms are the most prolific unicellular photoautotrophs found in our oceans today. Their secondary symbiotic origins, along with the evolutionary exchange of genetic material over time, has resulted in an abundance of extremely diverse marine phytoplankton. Their robust photosynthetic and metabolic capabilities, that are slowly being brought to light, have been found to be quite different from their terrestrial counterparts. As most of what we know today is based on decades of research on model land plants and green algae, research on diatoms holds a lot of promise for new insights on the evolution of aquatic photosynthesis.
To uncover the unique characteristics that allow these phytoplankton to outcompete other organisms for limited resources in their environment, I studied the changes in gene expression of low and high light acclimated Phaeodactylum tricornutum, to understand their responses to light stress. Analysis of the transcriptome of this model diatom revealed that strategies that improved the efficiency of light capture were upregulated in low light acclimated cells. Anabolic processes were downregulated, while catabolic metabolism, which regenerates reducing equivalents and ATP are upregulated, thus providing energy to the photon-limited cells. The most differentially expressed genes were predominantly uncharacterized proteins, reinforcing that what we know about marine photoacclimation at the molecular level is very limited. In this body of work, I have identified three proteins that are involved in light-intensity stimulated signal transduction cascades. The first encodes a light-specific soluble kinase, the second, an uncharacterized plastid transmembrane protein that appears to be under the regulation of the long noncoding natural antisense transcript (NAT) from its opposite strand, and the third is a MYB-like transcription factor that is a regulator of light harvesting complex gene expression in Phaeodactylum tricornutum.