Oxidative stress (OS) is generated by the imbalance between reactive oxygen species (ROS) and antioxidant enzyme activities, such as catalases, superoxide dismutases, and glutathione peroxidases. In the Y. lipolytica genome, three genes encoding catalases (CAT1, CAT2, and CAT3) have been identified; all three genes are transcriptionally active in cells grown under OS conditions. This study aimed to analyze whether the CAT1 and CAT2 genes exhibit a compensatory function that allows maintaining the functionality of the antioxidant response in Y. lipolytica cells lacking the CAT3 gene. The construction of the mutant strain (Ylcat3-Δ) was performed using Double-Joint PCR. OS was induced by the addition of H2O2 5 mM, ROS production was quantified by fluorescence using 2′,7′-dichlorofluorescein diacetate (DCFH-DA), and gene expression was analyzed by semi-quantitative RT-PCR in both parental (P01a) and mutant (Ylcat3-Δ) strains exposed or not to oxidative conditions. ROS production was lower in P01a cells than in Ylcat3-Δ cells when exposed to H2O2 5 mM. Also, under OS conditions, CAT1 gene expression levels decreased in both strains, whereas CAT2 gene expression increased in both types of cells. Under OS, both parental and Ylcat3-Δ strains showed similar growth rate, sensitivity to oxidative conditions and gene expression patterns, and it can be concluded that CAT3 gene deletion does not alter the transcriptional activity of CAT1 and CAT2 genes, suggesting that the compensatory function among the CAT genes of Y. lipolytica may not be limited to the presence/absence of CAT3 gene.
Quiñones-González et al. (Thu,) studied this question.