Rapid Triacylglycerol Turnover in Chlamydomonas reinhardtii Requires a Lipase with Broad Substrate Specificity

When deprived of nitrogen (N), the photosynthetic microalgaChlamydomonas reinhardtii accumulates large quantities of triacylglycerols (TAGs), making it a promising source of biofuel. Prominent transcriptional changes associated with the conditions leading to TAG accumulation have been found, suggesting that the key enzymes for TAG metabolism might be among those that fluctuate in their expression during TAG synthesis and breakdown. Using aSaccharomyces cerevisiae lipase null mutant strain for functional complementation, we identified theCrLIP1 gene fromChlamydomonas based on its ability to suppress the lipase deficiency-related phenotypes of the yeast mutant. InChlamydomonas , an inverse correlation was found between theCrLIP1 transcript level and TAG abundance whenChlamydomonas cultures were reversibly deprived of N. The CrLIP1 protein expressed and purified fromEscherichia coli exhibited lipolytic activity against diacylglycerol (DAG) and polar lipids. The lipase domain of CrLIP1 is most similar to two human DAG lipases, DAGLα and DAGLβ. The involvement of CrLIP1 inChlamydomonas TAG hydrolysis was corroborated by reducing the abundance of theCrLIP1 transcript with an artificial micro-RNA, which resulted in an apparent delay in TAG lipolysis when N was resupplied. Together, these data suggest that CrLIP1 facilitates TAG turnover inChlamydomonas primarily by degrading the DAG presumably generated from TAG hydrolysis.