Transcriptional regulator XYR1 activates the expression of cellobiose synthase to promote the production of cellulase from glucose

To investigate the transcriptional regulation of cellobiose synthase (CBS) in Rhizopus stolonifer. Transcription factor XYR1 was identified as responsible for the activation of cbs. In comparison with wild-type R. stolonifer, the deletion of XYR1 resulted in transcriptional down-regulation of cbs by approximately 40%, while XYR1 over-expression increased cbs transcription up to 175%. The highest FPA activity (1.8 IU/ml) was obtained in the XYR1-overexpressing strain OExyr1 cultivated in a 2% (m/V) glucose media, corresponding to a 96% increase compared with that of the parent strain (0.92 IU/ml). Moreover, cellulase synthesis was inhibited after cbs-inactivation mutation in OExyr1. XYR1 directly activates the transcription of cbs to promote cellulase production in R. stolonifer utilizing glucose as a substrate.