The Genome-Wide Identification and Expression Profiling of the HSF Gene Family in Ganoderma lucidum Under Temperature Stress.

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OBJECTIVE: In this study, the heat shock transcription factor (HSF) gene family in Ganoderma lucidum was systematically characterized. Using genomic and transcriptomic data, we identified HSF family members and investigated their expression patterns under temperature stress and their potential regulatory roles in triterpenoid biosynthesis.

METHODS: A genome-wide identification of HSF genes in G. lucidum was performed using bioinformatic approaches. A phylogenetic tree was constructed, and conserved motifs, gene structures, and protein tertiary structures were predicted. The relative expression levels of HSF genes and key mevalonate (MVA) pathway enzyme genes were examined by a quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) in mycelia subjected to temperature stress. Total triterpenoid content in fermented mycelia under temperature stress was determined using the vanillin-glacial acetic acid method.

RESULTS: Eight HSF family members ( GlHSF1 - GlHSF8 ) were identified in G. lucidum. Phylogenetic analysis revealed that GlHSF proteins were closely related to PoHSF from Pleurotus ostreatus. Transcriptomic analysis showed that HSF genes exhibited relatively high expression levels during the mature stage while being barely expressed during the mycelial stage. Under heat stress (42 °C), most GlHSF genes peaked at 18 h, with GlHSF2 showing the most pronounced response (approximately 13-fold upregulation). Downstream MVA pathway genes, including IDI, PMK, and MVD, were significantly upregulated at 24 h, whereas the upstream rate-limiting enzyme gene HMGR was continuously suppressed. Despite HMGR suppression, total triterpenoid content did not decrease significantly, likely due to the activation of downstream genes. Under cold stress (14 °C), the expression of most GlHSF and MVA pathway genes decreased, accompanied by a significant reduction in total triterpenoid content.

CONCLUSIONS: The HSF gene family was identified in the G. lucidum genome. Based on expression analysis, GlHSF2 showed the strongest response under heat stress, and its expression peak was correlated with the sequential activation of downstream genes in the MVA pathway. This suggests that GlHSF2 acts as a potential key regulatory node, differentially regulating upstream and downstream MVA pathway genes to influence triterpenoid biosynthesis under heat stress. These findings provide a theoretical basis for future research on the biological functions of GlHSF homeostasis.