Regulation of theacuFGene, Encoding Phosphoenolpyruvate Carboxykinase in the Filamentous FungusAspergillus nidulans

Abstract

Phosphoenolpyruvate carboxykinase (PEPCK) is a key enzyme required for gluconeogenesis when microorganisms grow on carbon sources metabolized via the tricarboxylic acid (TCA) cycle. Aspergillus nidulans acuF mutants isolated by their inability to use acetate as a carbon source specifically lack PEPCK. The acuF gene has been cloned and shown to encode a protein with high similarity to PEPCK from bacteria, plants, and fungi. The regulation of acuF expression has been studied by Northern blotting and by the construction of lacZ fusion reporters. Induction by acetate is abolished in mutants unable to metabolize acetate via the TCA cycle, and induction by amino acids metabolized via 2-oxoglutarate is lost in mutants unable to form 2-oxoglutarate. Induction by acetate and proline is not additive, consistent with a single mechanism of induction. Malate and succinate result in induction, and it is proposed that PEPCK is controlled by a novel mechanism of induction by a TCA cycle intermediate or derivative, thereby allowing gluconeogenesis to occur during growth on any carbon source metabolized via the TCA cycle. It has been shown that the facB gene, which mediates acetate induction of enzymes specifically required for acetate utilization, is not directly involved in PEPCK induction. This is in contrast to Saccharomyces cerevisiae, where Cat8p and Sip4p, homologs of FacB, regulate PEPCK as well as the expression of other genes necessary for growth on nonfermentable carbon sources in response to the carbon source present. This difference in the control of gluconeogenesis reflects the ability of A. nidulans and other filamentous fungi to use a wide variety of carbon sources in comparison with S. cerevisiae. The acuF gene was also found to be subject to activation by the CCAAT binding protein AnCF, a protein homologous to the S. cerevisiae Hap complex and the mammalian NFY complex.

Transcriptional Control of Gluconeogenesis in Aspergillus nidulans

“…The acuGD mutation resulted in elevated expression under all conditions, including in the presence of glycerol. Again, this is similar to results with the acuF-lacZ reporter where the acuG223 mutation was found to lead to increased expression (Hynes et al 2002). In addition, metabolism of glycerol to hexose phosphates dependent on FBP might result in carbon catabolite repression both directly and indirectly by preventing inducer formation in the wild-type and acuF205 backgrounds, but not in the acuGD strain.…”

“…Expression of an AcuF-LacZ reporter (Hynes et al 2002) was greatly reduced by the acuK248 and acuM301 mutations ( Figure 6A). As previously shown, the acuF205 mutation resulted in high levels of expression, a result interpreted as due to inducer accumulation.…”

“…The acuN356 mutation was found to result in loss of growth on a wide range of carbon sources requiring gluconeogenesis but was able to utilize glycerol (Figure 1). In this respect, the phenotype was identical to that of acuF205 strains lacking PEPCK (Armitt et al 1976;Hynes et al 2002). The acuN gene was cloned by complementation of the acuN356 mutation (see materials and methods).…”

“…The pattern of regulation is not consistent wih direct regulation by FacB. Furthermore, deletion analysis of the 59 region of acuF showed that the region responsible for induction lacks FacB-binding sites (Hynes et al 2002).…”

Cloning and Expression of the Pathogenicity-Related Genes of Oidium heveae in the Infection Process

“…RACB is a common element of ingrowth of haustoria in leaf epidermal cells and the GTPase-activating protein is important for the process [23]. The fungal growth-related Oh-PC2 encodes phosphoenolpyruvate carboxykinase (PEPCK), which is an important enzyme required for gluconeogenesis [24]. Our data seemed to demonstrate that only the Oh-PC2 gene expression was significantly up-regulated at 3 dpi and 30 dpi, indicating its importance in the metabolism of O. heveae during infection of rubber tree.…”