Molecular characterization of Hsf1 as a master regulator of heat shock response in the thermotolerant methylotrophic yeast Ogataea parapolymorpha.

Ogataea parapolymorpha (Hansenula polymorpha DL-1) is a thermotolerant methylotrophic yeast with biotechnological applications. Here, O. parapolymorpha genes whose expression is induced in response to heat shock were identified by transcriptome analysis and shown to possess heat shock elements (HSEs) in their promoters. The function of O. parapolymorpha HSF1 encoding a putative heat shock transcription factor 1 (OpHsf1) was characterized in the context of heat stress response. Despite exhibiting low sequence identity (26%) to its Saccharomyces cerevisiae homolog, OpHsf1 harbors conserved domains including a DNA binding domain (DBD), domains involved in trimerization (TRI), transcriptional activation (AR1, AR2), transcriptional repression (CE2), and a C-terminal modulator (CTM) domain. OpHSF1 could complement the temperature sensitive (Ts) phenotype of a S. cerevisiae hsf1 mutant. An O. parapolymorpha strain with an H221R mutation in the DBD domain of OpHsf1 exhibited significantly retarded growth and a Ts phenotype. Intriguingly, the expression of heat-shock-protein-coding genes harboring HSEs was significantly decreased in the H221R mutant strain, even under non-stress conditions, indicating the importance of the DBD for the basal growth of O. parapolymorpha. Notably, even though the deletion of C-terminal domains (ΔCE2, ΔAR2, ΔCTM) of OpHsf1 destroyed complementation of the growth defect of the S. cerevisiae hsf1 strain, the C-terminal domains were shown to be dispensable in O. parapolymorpha. Overexpression of OpHsf1 in S. cerevisiae increased resistance to transient heat shock, supporting the idea that OpHsf1 could be useful in the development of heat-shock-resistant yeast host strains.