Deletion of Non-histidine Domains of Histidine Kinase Diminishes the Infectivity of in an Oral Mucosal Model

Objectives: The histidine kinase (HK) and other protein kinases in are key players in the development of hyphae. This study is designed to determine the functional roles of the S_Tkc domain (protein kinase) and the GAF domain of in hyphal formation and mucosal invasion.

Methods: The domain mutants CHK25 ( Δ) and CHK26 ( Δ) were first constructed by the method and confirmed by sequencing and Southern blots. A mouse tongue infection model was used to evaluate the hyphal invasion and fungal loads in each domain mutant, full-gene deletion mutant CHK21 (ΔΔ), re-constituted strain CHK23 (Δ), and wild type (WT) from day 1 to day 5. The degree of invasion and damage to the oral mucosa of mice in each strain-infected group was evaluated and compared with germ tube rate and hyphal formation

Result: When compared with severe mucosal damage and massive hyphal formation in WT- or CHK23-infected mouse tongues, the deletion of S_Tkc domain (CHK25) caused mild mucosal damage, and fungal invasion was eliminated as we observed in full-gene mutant CHK21. However, the deletion of S_Tkc and GAF (CHK26) partially restored the hyphal invasion and mucosal tissue damage that were exhibited in WT and CHK23. Regardless of the results, the decreased hyphal formation and germ tube were less apparent and quite similar between CHK25 and CHK26, especially at the late stage of the log phase where CHK26 was closer to WT and CHK23. However, growth defect and hyphal impairment of both domain mutants were similar to CHK21 in the early stages.

Conclusion: Our data suggest that both protein kinase (S_Tkc) and GAF domains in are required for hyphal invasiveness in mucosal tissue. The appropriate initiation of cell growth and hyphal formation at the lag phase is likely mediated by these two functional domains of to maintain infectivity of .