Thieme Nils, Wu Vincent W, Dietschmann Axel, Salamov Asaf A, Wang Mei, Johnson Jenifer, Singan Vasanth R, Grigoriev Igor V, Glass N Louise, Somerville Chris R, Benz J Philipp
HFM, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany.
Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA USA.
Biotechnol Biofuels. 2017 Jun 12;10:149. doi: 10.1186/s13068-017-0807-z. eCollection 2017.
Pectin is an abundant component in many fruit and vegetable wastes and could therefore be an excellent resource for biorefinery, but is currently underutilized. Fungal pectinases already play a crucial role for industrial purposes, such as for foodstuff processing. However, the regulation of pectinase gene expression is still poorly understood. For an optimal utilization of plant biomass for biorefinery and biofuel production, a detailed analysis of the underlying regulatory mechanisms is warranted. In this study, we applied the genetic resources of the filamentous ascomycete species to screen for transcription factors that play a major role in pectinase induction.
The pectin degradation regulator-1 (PDR-1) was identified through a transcription factor mutant screen in . The Δ- mutant exhibited a severe growth defect on pectin and all tested pectin-related poly- and monosaccharides. Biochemical as well as transcriptional analyses of WT and the Δ- mutant revealed that while PDR-1-mediated gene induction was dependent on the presence of l-rhamnose, it also strongly affected the degradation of the homogalacturonan backbone. The expression of the endo-polygalacturonase - was greatly reduced in the Δ- mutant, while the expression levels of all pectate lyase genes increased. Moreover, a - overexpression strain displayed substantially increased pectinase production. Promoter analysis of the PDR-1 regulon allowed refinement of the putative PDR-1 DNA-binding motif.
PDR-1 is highly conserved in filamentous ascomycete fungi and is present in many pathogenic and industrially important fungi. Our data demonstrate that the function of PDR-1 in combines features of two recently described transcription factors in (RhaR) and (GaaR). The results presented in this study contribute to a broader understanding of how pectin degradation is orchestrated in filamentous fungi and how it could be manipulated for optimized pectinase production.
果胶是许多水果和蔬菜废弃物中的丰富成分，因此可能是生物炼制的优质资源，但目前未得到充分利用。真菌果胶酶已在工业用途中发挥关键作用，例如用于食品加工。然而，对果胶酶基因表达的调控仍知之甚少。为了最佳地利用植物生物质进行生物炼制和生物燃料生产，有必要对潜在的调控机制进行详细分析。在本研究中，我们利用丝状子囊菌物种的遗传资源筛选在果胶酶诱导中起主要作用的转录因子。
通过在……中的转录因子突变体筛选鉴定出果胶降解调节因子-1（PDR-1）。Δ-突变体在果胶以及所有测试的与果胶相关的多糖和单糖上表现出严重的生长缺陷。对野生型和Δ-突变体的生化及转录分析表明，虽然PDR-1介导的基因诱导依赖于L-鼠李糖的存在，但它也强烈影响同型半乳糖醛酸聚糖主链的降解。内切多聚半乳糖醛酸酶-的表达在Δ-突变体中大幅降低，而所有果胶酸裂解酶基因的表达水平均升高。此外，一个-过表达菌株显示果胶酶产量大幅增加。对PDR-1调控子的启动子分析有助于完善假定的PDR-1 DNA结合基序。
PDR-1在丝状子囊菌真菌中高度保守，存在于许多致病和工业上重要的真菌中。我们的数据表明，PDR-1在……中的功能结合了最近在……中描述的两种转录因子（RhaR）和……（GaaR）的特征。本研究结果有助于更广泛地理解丝状真菌中果胶降解是如何协调的，以及如何对其进行调控以优化果胶酶生产。
