Blocking β‐1,6‐glucan synthesis by deleting KRE6 and SKN1 attenuates the virulence of Candida albicans

• Published in: Molecular microbiology 2019-03, Vol.111 (3), p.604-620
• Main Authors: Han, Qi, Wang, Na, Yao, Guangyin, Mu, Chunhua, Wang, Yue, Sang, Jianli
• Format: Article
• Language: English
• Subjects: Abnormalities; Activation; Antifungal agents; Biofilms; Candida albicans; Cell surface; Cell walls; Clonal deletion; Endothelial cells; Fungi; Fungicides; Glucan; Growth conditions; Homology; Mutants; Proteins; Synthesis; Virulence; Western blotting
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14176

Summary β‐1,6‐glucan is an important component of the fungal cell wall. The β‐1,6‐glucan synthase gene KRE6 was thought to be essential in the fungal pathogen Candida albicans because it could not be deleted in previous efforts. Also, the role of its homolog SKN1 was unclear because its deletion caused no defects. Here, we report the construction and characterization of kre6Δ/Δ, skn1Δ/Δ and kre6Δ/Δ skn1Δ/Δ mutants in C. albicans. While deleting KRE6 or SKN1 had no obvious phenotypic consequence, deleting both caused slow growth, cell separation failure, cell wall abnormalities, diminished hyphal growth, poor biofilm formation and loss of virulence in mice. Furthermore, the GPI‐linked cell surface proteins Hwp1 and the invasin Als3 or Ssa1 were not detected in kre6Δ/Δ skn1Δ/Δ mutant. In GMM medium, RT‐qPCR and western blotting revealed a constitutive expression of KRE6 and growth conditions‐associated activation of SKN1. Like many hypha‐specific genes, SKN1 is repressed by Nrg1, but its activation does not involve the transcription factor Efg1. Dysregulation of SKN1 reduces C. albicans ability to damage epithelial and endothelial cells and attenuates its virulence. Given the vital role of β‐1,6‐glucan synthesis in C. albicans physiology and virulence, Kre6 and Skn1 are worthy targets for developing antifungal agents. It has long been thought that the β‐1,6‐glucan synthase gene KRE6 is essential and its homolog SKN1 is redundant in Candida albcians. We show that KRE6 is not essential and SKN1 is functional and can compensate for the function of KRE6. We, for the first time, reveal that in addition to the chitin and β‐1,3‐glucan synthesis machinery, β‐1,6‐glucan synthesis also possesses a compensatory strategy in C. albicans.