Evidence of a Critical Role for Cellodextrin Transporte 2 (CDT-2) in Both Cellulose and Hemicellulose Degradation and Utilization in <i>Neurospora crassa</i>

<div><p>CDT-1 and CDT-2 are two cellodextrin transporters discovered in the filamentous fungus <i>Neurospora crassa</i>. Previous studies focused on characterizing the role of these transporters in only a few conditions, including cellulose degradation, and the function of these two transporters is not yet completely understood. In this study, we show that deletion of <i>cdt-2</i>, but not <i>cdt-1</i>, results in growth defects not only on Avicel but also on xylan. <i>cdt-2</i> can be highly induced by xylan, and this mutant has a xylodextrin consumption defect. Transcriptomic analysis of the <i>cdt-2</i> deletion strain on Avicel and xylan showed that major cellulase and hemicellulase genes were significantly down-regulated in the <i>cdt-2</i> deletion strain and artificial over expression of <i>cdt-2</i> in <i>N. crassa</i> increased cellulase and hemicellulase production. Together, these data clearly show that CDT-2 plays a critical role in hemicellulose sensing and utilization. This is the first time a sugar transporter has been assigned a function in the hemicellulose degradation pathway. Furthermore, we found that the transcription factor XLR-1 is the major regulator of <i>cdt-2</i>, while <i>cdt-1</i> is primarily regulated by CLR-1. These results deepen our understanding of the functions of both cellodextrin transporters, particularly for CDT-2. Our study also provides novel insight into the mechanisms for hemicellulose sensing and utilization in <i>N. crassa</i>, and may be applicable to other cellulolytic filamentous fungi.</p>