Identification of a regulatory factor activating the xylanase promoter of the basidiomycetous yeast Pseudozyma antarctica and its application to enhance endogenous biodegradable plastic-degrading enzyme production via transcription factor multiplexing.

The basidiomycetous yeast Pseudozyma antarctica secretes the biodegradable plastic-degrading enzyme PaE. The xylanase promoter pPaXyn1 in P. antarctica is strongly induced by xylose. A P. antarctica reporter strain carrying the pPaXyn1 promoter-fused PaE gene (a PaE high-production cassette) produced a large amount of PaE in the presence of xylose. Accordingly, to further improve PaE productivity, this study aimed to isolate the transcription activation factor pPaXyn1. In total, 109 genes with Zn2Cys6-type DNA-binding domains were selected from the whole genome sequence of P. antarctica as candidate transcription factor genes. A set of strains was generated from the reporter strain in which each candidate transcription factor gene on the chromosome was disrupted. Among the disruptants, only the strain lacking the locus_tag PAN1_003r02005 (gene id: g2005) suppressed PaE production and did not show biodegradable plastic degrading activity. Moreover, a reporter strain with multiple copies of g2005 exhibited a 1.6-fold increase in PaE secretion. In addition, the strain also increased xylanase secretion. Overall, these results indicate that g2005 is a transcriptional activator of xylanase; hence, g2005 was named P. antarctica xylanase regulator 1 (PaXyr1). The amino acid sequence of g2005 is conserved only in the basidiomycete subphylum Smut (Ustilaginomycotina).