Transcription factors in Cenococcum geophilum and their potential roles in ectomycorrhizal symbiosis with Populus tomentosa

Cenococcum geophilum is one of the most widespread ectomycorrhizal (ECM) fungi, yet the transcriptional regulatory mechanisms underlying its symbiosis remain poorly understood. Here, we characterized transcription factor (TF) repertoire across six geographically distinct C. geophilum strains and compared them with those of Laccaria bicolor and L. japonica . Genome-wide analyses revealed that C. geophilum harbors relatively high TF abundance, with expansions of fungal Zn(2)-Cys(6) binuclear cluster domain and fungal TF domain families and strain-specific differences likely reflecting both sequencing approaches and ecological adaptation. Transcriptome profiling of C. geophilum Jacg10 strain during colonization of Populus tomentosa revealed stage-specific expression of TFs, particularly those involved in nitrogen metabolism, aromatic compound processing, and cell cycle regulation. Quantitative reverse transcription-PCR confirmed dynamic expression patterns of six candidate TFs. Among these, CgRlm1 was strongly induced at mid-symbiotic stages, showed transcriptional activation activity in yeast, and provided preliminary evidence for association with promoters of genes linked to cell wall remodeling. These findings indicate that C. geophilum has an expanded and diverse TF repertoire and that specific TFs, especially CgRlm1 , may play pivotal roles in regulating ECM development. Overall, this study highlights TFs as regulators of ECM symbiosis and provides a genomic and functional framework for investigating transcriptional regulation in non-model ECM fungi.