Context-dependent reprogramming of ALS adhesin expression in Candida albicans: a multi-inducer analysis linking...

Candida albicans employs the ALS (Agglutinin-Like Sequence) gene family to encode cell-surface adhesins that are central to host colonization, tissue invasion, and biofilm formation. Although individual ALS genes have been studied under specific conditions, no systematic, multi-inducer temporal analysis of the entire family has been reported to date. In this study, we present the first comprehensive temporal expression profiling of seven ALS genes (ALS1-ALS5, ALS7, and ALS9) under six host-relevant inducers, temperature (37 °C), neutral pH, serum, glucose, N-acetylglucosamine (NAG), and proline, across four time points (45 min, 90 min, 3 h, 6 h) in both yeast (30 °C) and hyphal (37 °C) growth phases. Morphological analysis confirmed that 37 °C and serum were the most potent hyphal inducers (94.13 ± 0.94% hyphae with serum at 37 °C). Quantitative PCR revealed a temporally stratified regulatory program: early-phase adhesins (ALS1, ALS2) showed transient induction during the first 90 min, whereas invasion-associated genes exhibited sustained late-phase activation. Notably, ALS3 displayed exceptional upregulation under glucose at 37 °C (25.17 ± 1.76-fold at 6 h; p < 0.001) and responded robustly to all inducers except serum. ALS7 reached 9.48-fold induction specifically under thermal stress, while ALS5 was preferentially expressed at 30 °C (6.70-fold under neutral pH), indicating niche-specific functional specialization. In silico promoter analysis linked these expression patterns to binding motifs for key transcription factors (Efg1, Cph1, Rim101, and Nrg1). Phylogenetic analysis revealed functional conservation of ALS2/ALS4 versus evolutionary divergence in ALS6/ALS7/ALS9. STRING-based protein interaction networks confirmed the central involvement of ALS proteins in adhesion and biofilm regulatory circuits. These findings establish a molecular framework for niche-specific virulence, identifying ALS3 as a prime therapeutic target for anti-adhesion strategies in invasive candidiasis. We hypothesize that C. albicans employs a temporally stratified and inducer-specific transcriptional program of the ALS family to adapt its surface architecture to diverse host microenvironments.