Regulation of the feruloyl esterase (faeA) gene from Aspergillus niger

Abstract

Feruloyl esterases can remove aromatic residues (e.g., ferulic acid) from plant cell wall polysaccharides (xylan, pectin) and are essential for complete degradation of these polysaccharides. Expression of the feruloyl esterase-encoding gene (faeA) from Aspergillus niger depends on D-xylose (expression is mediated by XlnR, the xylanolytic transcriptional activator) and on a second system that responds to aromatic compounds with a defined ring structure, such as ferulic acid and vanillic acid. Several compounds were tested, and all of the inducing compounds contained a benzene ring which had a methoxy group at C-3 and a hydroxy group at C-4 but was not substituted at C-5. Various aliphatic groups occurred at C-1. faeA expression in the presence of xylose or ferulic acid was repressed by glucose. faeA expression in the presence of ferulic acid and xylose was greater than faeA expression in the presence of either compound alone. The various inducing systems allow A. niger to produce feruloyl esterase not only during growth on xylan but also during growth on other ferulic acid-containing cell wall polysaccharides, such as pectin.

FIG. 1

Expression of faeA in the presence of aromatic compounds. A. niger N402 mycelium was incubated for 4 h in complete medium (blank), in complete medium containing 0.03% (mass/vol) fructose, and in complete medium containing different aromatic compounds at a concentration of 0.03% (mass/vol). The blots are Northern blots prepared as described in the text. 18S rRNA was used as an RNA loading control. Abbreviations: hydr., hydroxy; meth., methoxy; dimeth., dimethoxy; ppa, phenylpropionic acid.

FIG. 2

CreA repression of faeA expression. To determine the influence of the carbon catabolite repressor protein CreA on faeA expression, A. niger N402 and NW200 (CreA mutant) mycelia were incubated for 4 h in minimal medium containing different carbon sources. The blots are Northern blots prepared as described in the text. 18S rRNA was used as an RNA loading control. Abbreviations: glc, glucose; xyl, xylose; FA, ferulic acid.

FIG. 3

Interaction of different systems for induction of faeA expression. Relationships between XlnR and ferulic acid induction of faeA expression were studied by incubating A. niger N402 and NXA1-4 (XlnR mutant) mycelia for 2 h in minimal medium containing different carbon sources. The blots are Northern blots prepared as described in the text. 18S rRNA was used as an RNA loading control. Abbreviations: xyl, xylose; ara, arabinose; FA, ferulic acid.