A dual signalling pathway for the hypoxic expression of lipid genes, dependent on the glucose sensor Rag4, is revealed by the analysis of the KlMGA2 gene in Kluyveromyces lactis

Abstract

A dual signalling pathway for the hypoxic expression of lipid genes, dependent on the glucose sensor Rag4, is revealed by the analysis of the KlMGA2 gene in Kluyveromyces lactis In the respiratory yeast Kluyveromyces lactis, little is known about the factors regulating the metabolic response to oxygen shortage. After searching for homologues of characterized Saccharomyces cerevisiae regulators of the hypoxic response, we identified a gene that we named KlMGA2, which is homologous to MGA2. The deletion of KlMGA2 strongly reduced both the fermentative and respiratory growth rate and altered fatty acid composition and the unsaturation index of membranes. The reciprocal heterologous expression of MGA2 and KlMGA2 in the corresponding deletion mutant strains suggested that Mga2 and KlMga2 are functional homologues. KlMGA2 transcription was induced by hypoxia and the glucose sensor Rag4 mediated the hypoxic induction of KlMGA2. Transcription of lipid biosynthetic genes KlOLE1, KlERG1, KlFAS1 and KlATF1 was induced by hypoxia and was dependent on KlMga2, except for KlOLE1. Rag4 was required for hypoxic induction of transcription for both KlMga2-dependent (KlERG1) and KlMga2-independent (KlOLE1) structural genes.

Functional roles of the fatty acid desaturases encoded by KlOLE1, FAD2 and FAD3 in the yeast Kluyveromyces lactis

“…Genes encoding FAs desaturases in K. lactis have been identified previously: the D9-desaturase (Ole1) is encoded by KlOLE1 (KLLA0C05566g; Micolonghi et al, 2012). The D12 and !3 desaturases are respectively encoded by FAD2 and FAD3 genes (KLLA0F07095g and KLLA0B00473g).…”

“…Studies on this yeast indicate that glucose and oxygen signalling and responses are linked (Micolonghi et al, 2011). This regulation also involves biosynthesis of FAs through the activity of the hypoxic regulator KlMga2 (Micolonghi et al, 2012;Ottaviano et al, 2015). Similar to K. lactis, PUFAs are present also in other ascomycetous yeasts, in which desaturase enzyme and/or genes have been previously studied, such as Pichia pastoris (Yu et al, 2012), Hansenula polymorpha (Sangwallek et al, 2014) and Saccharomyces kluyveri (Oura & Kajiwara, 2008), and in basidiomycetes as well (Rossi et al, 2009).…”

“…Transcription of genes involved in FAs biosynthesis is regulated by environmental stimuli such as hypoxia, temperature (Micolonghi et al, 2012;Ottaviano et al, 2015) and ethanol (Fig. S5).…”

“…The composition of their FAs is enriched with the polyunsaturated linoleic and a-linolenic acids generated by the D12 (Fad2) and !3 (Fad3) desaturases (Kainou et al, 2006;Micolonghi et al, 2012). Studies on this yeast indicate that glucose and oxygen signalling and responses are linked (Micolonghi et al, 2011).…”

Autoregulation of the Kluyveromyces lactis pyruvate decarboxylase gene KlPDC1 involves the regulatory gene RAG3

“…Moreover, the fermentative pathway is activated in the absence of oxygen (Kiers et al, 1998), and KlPDC1 transcription is also induced by hypoxia (Destruelle et al, 1999;Camattari et al, 2007). This hypoxic induction is independent of the presence of glucose but requires the glucose sensor Rag4 (Micolonghi et al, 2011(Micolonghi et al, , 2012. The KlPDC1 regulatory genetic elements and mutants have been exploited in this yeast as tools for the production of heterologous proteins (Salani & Bianchi, 2006;Camattari et al, 2007;Ranieri et al, 2009).…”