Role of AcuM and AcuK Transcription Factors in Regulation of Target Genes Involving Iron Assimilation and Gluconeogenesis in Talaromyces marneffei

Abstract

Talaromyces marneffei is a dimorphic fungus that causes opportunistic infections in immunocompromised patients. The fungus grows in the mold form at 25-30°C and yeast form at 37°C. Most infected persons are those with HIV infection. The infection is assumed to be started by inhalation of conidia into lungs. The conidia were engulfed by macrophages, but they could withstand the killing mechanism within phagosomes and grow into fission yeast inside the macrophages. The survival mechanisms of T. marneffei in phagosomes of macrophages are expected to primarily due to their ability to withstand the sterilization process and the ability to use alternative carbon sources in growing and replication. The ability to adapt in the environment with oxidative stress or nutrient limitation contributes to the pathogenicity of this fungus. AcuK and AcuM Zn(II)2Cys6 transcription factor could bind to the specific DNA sequence to control gene expression. AcuK and AcuM transcription factors control the gene expression involving gluconeogenesis in Aspergillus fumigatus and Aspergillus nidulans. Additionally, they could control iron acquisition process in A. fumigatus. Even both fungi belongs to the same genus, AcuK and AcuM function differently. Talaromyces marneffei is the pathogenic dimorphic fungus which has close relation to the Aspergilli; however, no report on how AcuK and AcuM function. This study aimed to investigate the AcuK and AcuM in gluconeogenesis and iron acquisition and define their target genes in T. marneffei. The deletion strain, ΔacuM was generated in this study. Then, the expression of expected target genes were compared in ΔacuM, ΔacuK (from previous study) and wild type. The results found that ΔacuM and ΔacuK mutant strains could not grow in iron limiting condition. Interestingly, ΔacuM mutant effect the growth in high iron concentration and 37 oC. Both of ΔacuM and ΔacuK mutant could not grow in medium containing gluconeogenic substrates. This study determined the target genes under controlled by the AcuM and AcuK in iron assimilation process. Both transcription factors are important for controlling of siderophore biosynthesis via inhibition of SreA and activation of HapX as found in A. fumigatus. Moreover, AcuM alone could control reductive iron assimilation (RIA) process via ftrA and fetC. Both genes were downregulated in ΔacuM. Identification of possible target genes in gluconeogenesis process demonstrated that facB and alcB might have been controlled by AcuM while prnD might have been controlled by AcuM and/or AcuK. In addition, AcuM and AcuK transcription factors play an important role in gluconeogenesis in the usage of gluconeogenic substrates as the alternative carbon sources. Moreover, this study found that AcuM and AcuK transcription factor could have working together or independently in control of iron homeostasis and carbon consuming pathway. However, single gene deletion led to completely loss of ability to grow in iron limitation and gluconeogenic carbon sources. This result suggested that disruption of AcuK or AcuM could attenuate the virulence. AcuM and AcuK transcription factors are specific to Ascomycetous fungi, therefore blocking the function of AcuK and AcuM transcription factors can be the targets for prevention or treatment of the infection due to T. marneffei in the future.