Dal81 Regulates Expression of Arginine Metabolism Genes in Candida parapsilosis.

Siobhan A Turner,Geraldine Butler,Qinxi Ma,Kontxi Martinez De San Vicente,Mihaela Ola,Aaron P Mitchell

doi:10.1128/msphere.00028-18

Abstract

Fungi can use a wide variety of nitrogen sources. In the absence of preferred sources such as ammonium, glutamate, and glutamine, secondary sources, including most other amino acids, are used. Expression of the nitrogen utilization pathways is very strongly controlled at the transcriptional level. Here, we investigated the regulation of nitrogen utilization in the pathogenic yeast Candida parapsilosis. We found that the functions of many regulators are conserved with respect to Saccharomyces cerevisiae and other fungi. For example, the core GATA activators GAT1 and GLN3 have a conserved role in nitrogen catabolite repression (NCR). There is one ortholog of GZF3 and DAL80, which represses expression of genes in preferred nitrogen sources. The regulators PUT3 and UGA3 are required for metabolism of proline and γ-aminobutyric acid (GABA), respectively. However, the role of the Dal81 transcription factor is distinctly different. In S.cerevisiae, Dal81 is a positive regulator of acquisition of nitrogen from GABA, allantoin, urea, and leucine, and it is required for maximal induction of expression of the relevant pathway genes. In C.parapsilosis, induction of GABA genes is independent of Dal81, and deleting DAL81 has no effect on acquisition of nitrogen from GABA or allantoin. Instead, Dal81 represses arginine synthesis during growth under preferred nitrogen conditions. IMPORTANCE Utilization of nitrogen by fungi is controlled by nitrogen catabolite repression (NCR). Expression of many genes is switched off during growth on nonpreferred nitrogen sources. Gene expression is regulated through a combination of activation and repression. Nitrogen regulation has been studied best in the model yeast Saccharomyces cerevisiae. We found that although many nitrogen regulators have a conserved function in Saccharomyces species, some do not. The Dal81 transcriptional regulator has distinctly different functions in S.cerevisiae and C.parapsilosis. In the former, it regulates utilization of nitrogen from GABA and allantoin, whereas in the latter, it regulates expression of arginine synthesis genes. Our findings make an important contribution to our understanding of nitrogen regulation in a human-pathogenic fungus.

Highlights

Fungi can use a wide variety of nitrogen sources
We first tested if gene expression is subject to nitrogen catabolite repression in C. parapsilosis CLIB214 in a manner similar to that seen with other fungi by comparing the levels of gene expression of wild-type cells growing in media containing a preferred nitrogen source and in media with a nonpreferred source (YNB with glucose and isoleucine)
Genes involved in amino acid transport and synthesis, especially those involved in arginine biosynthesis (e.g., ARG1, ARG3, ARG5,6 and CPA2), were upregulated

Summary

Introduction

Fungi can use a wide variety of nitrogen sources. In the absence of preferred sources such as ammonium, glutamate, and glutamine, secondary sources, including most other amino acids, are used. There is one ortholog of GZF3 and DAL80, which represses expression of genes in preferred nitrogen sources. In S. cerevisiae, Dal is a positive regulator of acquisition of nitrogen from GABA, allantoin, urea, and leucine, and it is required for maximal induction of expression of the relevant pathway genes. The Dal transcriptional regulator has distinctly different functions in S. cerevisiae and C. parapsilosis In the former, it regulates utilization of nitrogen from GABA and allantoin, whereas in the latter, it regulates expression of arginine synthesis genes. Preferred nitrogen sources include glutamate, glutamine, ammonium, and peptones [1] When these sources are available, expression of genes associated with the utilization of poor nitrogen sources is repressed, in a process called nitrogen catabolite repression (NCR) [2,3,4,5]. Many proteins, including membrane transporters that import ammonium [15, 16], amino acid transporters [17], and secreted proteases that degrade environmental proteins to release amino acids [4], are subject to NCR at both the mRNA and protein levels

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Conclusion