Specific expression patterns of xyl1, xyl2 and xyl3 in response to different sugars in Pichia stipitis

The effects of two different sugars (glucose and xylose) on the expression levels and patterns of xylose reductase (xyl1), xylitol dehydrogenase (xyl2) and xylulokinase (xyl3) genes were analyzed using Pichia stipitis. A significant increase in mRNA levels of xyl1 was observed after 6 hours growth in culture conditions using xylose as a sole carbon source, but expressions of the three genes were not influenced by normal culture media with glucose. In addition expression levels of xyl2 and xyl3 were not observed during the entire culture period during which xylose was added. It also was found that the expression level of xyl1 increased as a function of the xylose concentration (40, 60, 80 g/l) used in this study, indicating that xyl1 expression sensitively responded to xylose presence in the culture media. Although the induced level of xyl2 increased slightly after 48 hours in the xylose-supplemented culture conditions, the expression level of xyl2 was not observed in the xylitol-supplemented culture conditions. Finally, considering the expression of each gene in response to glucose or xylose, the absolute expression levels of the three genes indicate that xyl1 is induced primarily by exposure to xylose.