近日，国际学术刊物Eukaryotic Cell发表了中科院天津工业生物技术研究所田朝光课题组关于半纤维素降解调控机制的研究论文。田朝光课题组与加州大学合作，解析了粗糙脉孢菌半纤维素降解基因xlr-1调控靶体，揭示了粗糙脉孢菌与其它丝状真菌在半纤维素降解和调控机制上的相似性和不同点。
半纤维素是仅次于纤维素的第二大丰富的可再生生物质资源。丝状真菌对半纤维素的降解作用需要很多不同的酶，这些酶是由生物质降解后的分子或者其衍生物诱导产生的，并且主要在转录水平进行调控。但是人们对具体的调控机理还不是很清楚，为了更好地利用半纤维素，研究这一机理也就成为必然。
研究人员在粗糙脉孢菌体系为研究对象，以木聚糖为唯一碳源，通过转录组学分析鉴定了353个基因被半纤维素显著诱导。在预测的19个半纤维素酶基因中，8个基因显著诱导表达。
通过进一步的分泌蛋白质组学和基因敲除突变体库的筛选，研究人员发现，在曲霉和木霉上的转录因子XlnR/Xyr1的同源基因NCU06971是粗糙脉孢菌半纤维素主调控因子，并命名为xlr-1（木聚糖酶调节因子1）。xlr-1缺失突变株在木聚糖和木糖上都不能生长，但是可以在纤维素上生长并且只对纤维素水解能力有轻微影响。
为了研究半纤维素降解的调节机制，该研究组在木糖、木聚糖分解和纤维素分解条件下探明了XLR-1蛋白的调控靶体，XLR-1蛋白在粗糙脉孢菌中调节主要的半纤维素酶基因，但对部分纤维素酶的完全诱导有影响。此项研究对半纤维素降解调节机制的研究具有重要参考意义。（生物谷Bioon.com）
doi:10.1128/EC.05327-11
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Deciphering transcriptional regulatory mechanisms associated with hemicellulose degradation in Neurospora crassa
Jianping Sun, Chaoguang Tian, Spencer Diamond and N. Louise Glass
Hemicellulose, the second most abundant plant biomass fraction after cellulose, is widely viewed as a potential substrate for the production of liquid fuels and other value-added materials. Degradation of hemicellulose by filamentous fungi requires production of many different enzymes, which are induced by biopolymers or its derivatives and regulated mainly at the transcriptional level through transcription factors (TFs). Neurospora crassa, a model filamentous fungus, expresses and secretes enzymes required for plant cell wall deconstruction. To better understand genes specifically associated with degradation of hemicellulose, we applied secretome and transcriptome analysis to N. crassa grown on beechwood xylan. We identified 34 secreted proteins and 353 genes with elevated transcription on xylan. The xylanolytic phenotype of strains with deletions in genes identified from the secretome and transcriptome analysis of wild type was assessed, revealing functions for known and unknown proteins associated with hemicellulose degradation. By evaluating phenotypes of strains containing deletions of predicted TF genes in N. crassa, we identified a TF (xylan degradation regulator-1) essential for hemicellulose degradation that is an ortholog to XlnR/Xyr1 in Aspergillus and Trichoderma species, respectively, a major transcriptional regulator of genes encoding both cellulases and hemicellulases. Deletion of xlr-1 in N. crassa abolished growth on xylan and xylose, but growth on cellulose and cellulolytic activity was only slightly affected. To determine regulatory mechanisms for hemicellulose degradation, we explored the transcriptional regulon of XLR-1 under xylose, xylanolytic and cellulolytic conditions. XLR-1 regulated only some predicted hemicellulase genes in N. crassa and was required for a full induction of several cellulase genes. Hemicellulase gene expression was induced by a combination of release from carbon catabolite repression (CCR) and induction. This systematic analysis illustrates the similarities and differences in regulation of hemicellulose degradation among filamentous fungi.
