Light-Stress Response Mediated by the Transcription Factor KlMga2 in the Yeast Kluyveromyces lactis

Light Stress in Yeasts: Signaling and Responses in Creatures of the Night

Living organisms on the surface biosphere are periodically yet consistently exposed to light. The adaptive or protective evolution caused by this source of energy has led to the biological systems present in a large variety of organisms, including fungi. Among fungi, yeasts have developed essential protective responses against the deleterious effects of light. Stress generated by light exposure is propagated through the synthesis of hydrogen peroxide and mediated by regulatory factors that are also involved in the response to other stressors. These have included Msn2/4, Crz1, Yap1, and Mga2, thus suggesting that light stress is a common factor in the yeast environmental response.

The UPC2 gene in Kluyveromyces lactis stress adaptation

KlUpc2p, a transcription factor belonging to the fungal binuclear cluster family, is an important regulator of ergosterol biosynthesis and azole drug resistance in Kluyveromyces lactis. In this work, we show that the absence of KlUpc2p generates Rag^- phenotype and modulates the K. lactis susceptibility to oxidants and calcofuor white. The KlUPC2 deletion leads to increased expression of KlMGA2 gene, encoding an important regulator of hypoxic and lipid biosynthetic genes in K. lactis and also KlHOG1 gene. The absence of KlUpc2p does not lead to statistically significant changes in glycerol, corroborating the expression of KlGPD1 gene, encoding NAD⁺-dependent glycerol-3-phosphate dehydrogenase, that is similar in both the deletion mutant and the parental wild-type strain. Increased sensitivity of Klupc2 mutant cells to brefeldin A accompanied with significant increase in KlARF2 gene expression point to the involvement of KlUpc2p in intracellular signaling. Our observations highlight the connections between ergosterol and fatty acid metabolism to modulate membrane properties and point to the possible involvement of KlUpc2p in K. lactis oxidative stress response.