Transcriptional activator of the pentose catabolic pathway (PCP). Involved in the induction of a variety of PCP enzymes during growth on D-xylose. Has no effect on cellulolytic and xylanolytic enzyme activities. Reduces growth on D-xylose and xylan, but not on L-arabinose or arabinan. Belongs to the xlnR/xlr1 family.