AUTHOR=Feng Yahui , Bian Shaodong , Pang Zhiping , Wen Yiyang , Calderone Richard , Li Dongmei , Shi Dongmei 

TITLE=Deletion of Non-histidine Domains of Histidine Kinase CHK1 Diminishes the Infectivity of Candida albicans in an Oral Mucosal Model

JOURNAL=Frontiers in Microbiology

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.855651

DOI=10.3389/fmicb.2022.855651

ISSN=1664-302X

ABSTRACT=Objectives: The current study is designed to determine the functional roles of the S_Tkc domain (protein kinase) and the GAF domain of CHK1 in mucosal invasion. 
Methods: The domain mutants CHK25 (ΔS_TkcCHK1/Δchk1) and CHK26 (ΔS_TkcΔgafCHK1/Δchk1) were first constructed by his1-URA3-his1 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 (chk1Δ/chk1Δ), re-constituted strain CHK23 (chk1Δ/CHK1) and wild type (WT). The degree of invasion and damage to the oral mucosa of mice in each infected mouse were evaluated in vivo and compared to germ tube rate and hyphal formation in vitro.     
Result： When compared with severe mucosal damage and massive hyphal formation in WT- or CHK23-infected mouse tongues, deletion of S_Tkc domain (CHK25) caused no apparent mucosal damage and fungal invasion was totally eliminated as we observed in full-gene mutant CHK21. However, 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 in vivo results, the decreased hyphal formation and germ tube in vitro were 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 protein kinase and GAF domains in CHK1 are both required for hyphal invasiveness in mucosal tissue. The appropriate initiation of cell growth and hyphal formation at lag phase is likely mediated by these two functional domains of CHK1 to maintain infectivity of C. albicans in vivo.