S16: Identification of an algal lipid accumulation trigger for overproduction of lipid in transgenic microalgae

A common algal physiological response to nitrogen limitation is production of elevated levels of lipids, building blocks that can be used for fuel production. However, a fundamental roadblock exists for using nitrogen limitation as a means of increasing lipids and therefore the fuel component of algae. Nitrogen stress also causes a drastic reduction in the growth rate of most algae, along with other phenotypes such as photosystem breakdown and chlorophyll degradation. Using a transcriptomics approach, we have identified a putative transcription factor from Chlamydomonas reinhardtii (SN03) that, when overexpressed in Chlamydomonas, triggers the algae to accumulate lipid at levels similar to algae under nitrogen-limitation. The dramatic reduction in growth rate and the breakdown of the photosystem that accompany nitrogen stress in algae are not evident in the overexpression line, suggesting that lipid accumulation is unlinked from growth through the action of SN03. Taken together, this suggests that SN03 is the key transcriptional regulator of stress-induced lipid accumulation, the elusive algal lipid trigger.