PNNL

Abstract

Background: Fungi accumulate lipids in a manner dependent on the quantity and quality of the nitrogen source on which they are growing. In the oleaginous yeast Yarrowia lipolytica, growth on a complex source of nitrogen enables rapid growth and limited accumulation of neutral lipids while growth on a simple nitrogen source promotes lipid accumulation in large lipid droplets. Here we examined the role of nitrogen catabolite repression, and its regulation by GATA zinc-finger transcription factors on lipid metabolism in Y. lipolytica. Results: The genome of Y. lipolytica encodes four GATA and two GATA-like transcription factors which we functionally characterized. Deletion of the GATA transcription factor genes Yali0C22682g and Yali0F17886g resulted in nitrogen source specific growth defects and greater accumulation of lipids when growing on a simple nitrogen source. Deletion of Yali0D20482g, which is most similar to activators of genes repressed by nitrogen catabolite repression in filamentous ascomycetes, did not affect growth on the nitrogen sources tested. We examined gene expression of wild-type and GATA transcription factor mutants on simple and complex nitrogen sources and found that expression of enzymes involved in malate metabolism, beta-oxidation, and ammonia utilization are strongly up-regulated on a simple nitrogen source. Deletion of Yali0C22682g results in overexpression of genes with ‘GATAA’ sites in their promoters while Yali0F17886g is required for expression of ammonia utilization genes but does not grossly affect the transcription level of genes predicted to be controlled by nitrogen catabolite repression. Conclusions: The GATA binding zinc-finger transcription factors Yali0C22682g and Yali0F17886g regulate nitrogen utilization in Y. lipolytica. Yali0C22682g functions as a general repressor of genes controlled by nitrogen catabolite repression while Yali0F17886g is an activator of ammonia utilization genes. Both GATA transcription factor mutants exhibit decreased expression of genes predicted to be controlled by carbon catabolite repression, including genes for beta-oxidation, highlighting the complex interplay between regulation of carbon, nitrogen, and lipid metabolism.