现有策略构建的重组酿酒酵母木糖代谢速率只达到葡萄糖代谢速率的50%左右，这和菌株利用木糖时细胞碳代谢途径的活性处于不利于发酵的状态有关。酵母通过葡萄糖感应系统调节细胞碳代谢途径，研究显示，该系统对木糖有部分响应，但涉及途径和响应水平尚不明确。葡萄糖木糖共发酵时，葡萄糖竞争糖转运蛋白使木糖代谢速率降低，但有趣的是，葡萄糖耗尽后木糖代谢速率仍远低于木糖为唯一碳源时的水平。基于此，本项目拟展开两个方面的工作：①通过测试葡萄糖感应系统各途径典型受控元件在木糖中的被调节状态，研究各途径对木糖信号的响应及程度；②通过比较菌株在共发酵中木糖利用阶段和木糖为唯一碳源时生理、代谢、及组学差异，结合共发酵过程葡萄糖耗尽前后营养转换事件信息，主要从葡萄糖感应途径、主要代谢途径活性、以及细胞能量和氧化还原状态三个方面研究葡萄糖代谢后继效应影响木糖转化效率的机制，为进一步提高菌株木糖代谢效率提供理论依据。

The high-efficienct xylose conversion is one of the key technologies for the second-generation fuel ethanol production. In recent years, the xylose metabolism capacity of recombinant Saccharomyces cerevisiae has been greatly improved through genetic engineering and adaptive evolution. However, the xylose metabolism rate of strain only approach to 50% of glucose metabolism rate. It was strongly suggested that the sub-effecient xylose metabolism dut to the incomplete activation of glucose sensing network. Nonetheless, the direct evidences are necessory to demonstrate this viewpoint, and the response level need to be revealed. Another important phenomenon, which can be commonly observed in engineered strains with different genetic background, is that the xylose consumption rate is much lower during the xylose phase in glucose-xylose co-fermentation than in the fermentation using xylose as the sole carbon source. Therefore, in present project, two aspects of work will be done to improve the xylose conversion efficiency. ① Confirming the pathways in the glucose sensing system that response to xylose signal and determine their response level; ② Studying the nutrient conversion events happened during the phase shifts in the glucose-xylose co-fermentation; compare the cell physiological states when the cell keeps in the xylose phase in glucose-xylose co-fermentation and xylose fermentation, respecitively. Basing on the data we get, the mechanism why the glucose metabolism has subsequent effect on xylose utilization will be uncovered in the aspects of glucose sensing network, the expressin of genes involved in the main metabolic pathway, and the level and phosphorylation of key proteines. The further engineered strain with higher xylose fermentation efficency will be obtained basing on the knowledge we get.