  Citation: Lai, W.-C.; Hsu, H.-C.; Cheng, C.-W.; Wang, S.-H.;Li, W.C.; Hsieh, P.-S.; Tseng, T.-L.; Lin, T.-H.; Shieh, J.-C. Filament Negative Regulator CDC4 Suppresses Glycogen Phosphorylase Encoded GPH1 That Impacts the Cell Wall-Associated Features in Candida albicans. J. Fungi 2022, 8, 233. https:// doi.org/10.3390/jof8030233 Academic Editors: Michaela Lackner and Mikhail Keniya Received: 28 January 2022 Accepted: 22 February 2022 Published: 26 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Fungi Journal of Article Filament Negative Regulator CDC4 Suppresses Glycogen Phosphorylase Encoded GPH1 That Impacts the Cell Wall-Associated Features in Candida albicans Wei-Chung Lai 1 , Hsiao-Chi Hsu 1 , Chun-Wen Cheng 2 , Shao-Hung Wang 3 , Wan Chen Li 1 , Po-Szu Hsieh 1 , Tzu-Ling Tseng 1 , Ting-Hui Lin 1 and Jia-Ching Shieh 1,4,5, * 1 Department of Biomedical Sciences, Chung Shan Medical University, Taichung City 40201, Taiwan, China; workman_pum250@hotmail.com (W.-C.L.); cookiechi413@gmail.com (H.-C.H.); wanwan9121@hotmail.com (W.C.L.); catstyle0626@hotmail.com (P.-S.H.); linda740410@hotmail.com (T.-L.T.); thlin@csmu.edu.tw (T.-H.L.) 2 Institute of Medicine, Chung Shan Medical University, Taichung City 40201, Taiwan, China; cwcheng@csmu.edu.tw 3 Department of Microbiology, Immunology and Biopharmaceuticals, National Chiayi University, Chiayi 60004, Taiwan, China; shwang@mail.ncyu.edu.tw 4 Department of Medical Research, Chung Shan Medical University Hospital, Taichung City 40201, Taiwan, China 5 Immunology Research Center, Chung Shan Medical University, Taichung City 40201, Taiwan, China * Correspondence: jcs@csmu.edu.tw; Tel.: +886-424-730-022 (ext. 11806); Fax: +886-424-757-412 Abstract: We have previously identified Candida albicans GPH1 (orf19.7021) whose protein product was associated with C. albicans Cdc4. The GPH1 gene is a putative glycogen phosphorylase because its Saccharomyces cerevisiae homolog participates in glycogen catabolism, which involves the synthesis of β-glucan of the fungal cell wall. We made a strain whose CaCDC4 expression is repressed, and GPH1 is constitutively expressed. We established a GPH1 null mutant strain and used it to conduct the in vitro virulence assays that detect cell wall function. The in vitro virulence assay is centered on biofilm formation in which analytic procedures are implemented to evaluate cell surface hydrophobicity; competence, either in stress resistance, germ tube formation, or fibronection association; and the XTT-based adhesion and biofilm formation. We showed that the constitutively expressed GPH1 partially suppresses filamentation when the CaCDC4 expression is repressed. The C. albicans Gph1 protein is reduced in the presence of CaCdc4 in comparison with the absence of CaCdc4. Compared with the wild-type strain, the gph1Δ/gph1Δ mutant displayed a reduction in the capability to form germ tubes and the cell surface hydrophobicity but an increase in binding with fibronectin. Compared with the wild-type strain, the gph1Δ/gph1Δ mutant showed a rise in adhesion, the initial stage of biofilm formation, but displayed a similar capacity to form a mature biofilm. There was no major impact on the gph1Δ/gph1Δ mutant regarding the conditions of cell wall damaging and TOR pathway-associated nutrient depletion. We conclude that GPH1, adversely regulated by the filament suppressor CDC4, contributes to cell wall function in C. albicans. Keywords: Candida albicans; CaCDC4; GPH1; morphogenesis; cell wall 1. Introduction The opportunistic human fungal pathogen Candida albicans [1] is a member of the normal microflora on mucosal surfaces in healthy persons [2] but can cause vulvovaginal candidiasis in women [3,4] and oral [5,6] and systemic candidiasis in debilitated and im- munocompromised patients [7–10]. C. albicans can grow in a wide variety of morphological forms, from the ellipsoid blastospore to various filamentous types [11–14]. A great effort has been made to reveal the underlying mechanism of C. albicans morphogenesis because it is proven to be coupled with virulence and pathogenesis [15–18]. However, research J. Fungi 2022, 8, 233. https://doi.org/10.3390/jof8030233 https://www.mdpi.com/journal/jof