SOA genes encode proteins controlling lipase expression in response to triacylglycerol utilization in the yeast Yarrowia lipolytica

The oleaginous yeast Yarrowia lipolytica efficiently metabolizes hydrophobic substrates such as alkanes, fatty acids or triacylglycerol. This yeast has been identified in oil-polluted water and in lipid-rich food. The enzymes involved in lipid breakdown, for use as a carbon source, are known, but the molecular mechanisms controlling the expression of the genes encoding these enzymes are still poorly understood. The study of mRNAs obtained from cells grown on oleic acid identified a new group of genes called SOA genes (specific for oleic acid). SOA1 and SOA2 are two small genes coding for proteins with no known homologs. Single- and double-disrupted strains were constructed. Wild-type and mutant strains were grown on dextrose, oleic acid and triacylglycerols. The double mutant presents a clear phenotype consisting of a growth defect on tributyrin and triolein, but not on dextrose or oleic acid media. Lipase activity was 50-fold lower in this mutant than in the wild-type strain. The impact of SOA deletion on the expression of the main extracellular lipase gene (LIP2) was monitored using a LIP2-β-galactosidase promoter fusion protein. These data suggest that Soa proteins are components of a molecular mechanism controlling lipase gene expression in response to extracellular triacylglycerol.