Zhao Zhen, Gu Shuying, Liu Defei, Liu Dandan, Chen Bingchen, Li Jingen, Tian Chaoguang
Key Laboratory of Engineering Biology for Low-carbon Manufacturing, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China.
National Technology Innovation Center of Synthetic Biology, Tianjin, 300308, China.
Biotechnol Biofuels Bioprod. 2023 Apr 3;16(1):58. doi: 10.1186/s13068-023-02313-3.
Filamentous fungi with the ability to use complex carbon sources has been developed as platforms for biochemicals production. Myceliophthora thermophila has been developed as the cell factory to produce lignocellulolytic enzymes and plant biomass-based biofuels and biochemicals in biorefinery. However, low fungal growth rate and cellulose utilization efficiency are significant barriers to the satisfactory yield and productivity of target products, which needs our further exploration and improvement.
In this study, we comprehensively explored the roles of the putative methyltransferase LaeA in regulating mycelium growth, sugar consumption, and cellulases expression. Deletion of laeA in thermophile fungus Myceliophthora thermophila enhanced mycelium growth and glucose consumption significantly. Further exploration of LaeA regulatory network indicated that multiple growth regulatory factors (GRF) Cre-1, Grf-1, Grf-2, and Grf-3, which act as negative repressors of carbon metabolism, were regulated by LaeA in this fungus. We also determined that phosphoenolpyruvate carboxykinase (PCK) is the core node of the metabolic network related to fungal vegetative growth, of which enhancement partially contributed to the elevated sugar consumption and fungal growth of mutant ΔlaeA. Noteworthily, LaeA participated in regulating the expression of cellulase genes and their transcription regulator. ΔlaeA exhibited 30.6% and 5.5% increases in the peak values of extracellular protein and endo-glucanase activity, respectively, as compared to the WT strain. Furthermore, the global histone methylation assays indicated that LaeA is associated with modulating H3K9 methylation levels. The normal function of LaeA on regulating fungal physiology is dependent on methyltransferase activity.
The research presented in this study clarified the function and elucidated the regulatory network of LaeA in the regulation of fungal growth and cellulase production, which will significantly deepen our understanding about the regulation mechanism of LaeA in filamentous fungi and provides the new strategy for improvement the fermentation properties of industrial fungal strain by metabolic engineering.
具有利用复杂碳源能力的丝状真菌已被开发为生物化学品生产的平台。嗜热毁丝霉已被开发为细胞工厂，用于在生物精炼中生产木质纤维素分解酶以及基于植物生物质的生物燃料和生物化学品。然而，真菌生长速率低和纤维素利用效率低是目标产物产量和生产率达到理想水平的重大障碍，这需要我们进一步探索和改进。
在本研究中，我们全面探索了假定的甲基转移酶LaeA在调节菌丝体生长、糖消耗和纤维素酶表达中的作用。嗜热真菌嗜热毁丝霉中laeA的缺失显著增强了菌丝体生长和葡萄糖消耗。对LaeA调控网络的进一步探索表明，多个生长调节因子（GRF）Cre-1、Grf-1、Grf-2和Grf-3作为碳代谢的负阻遏物，在该真菌中受LaeA调控。我们还确定磷酸烯醇式丙酮酸羧激酶（PCK）是与真菌营养生长相关的代谢网络的核心节点，其增强部分促成了突变体ΔlaeA糖消耗增加和真菌生长。值得注意的是，LaeA参与调节纤维素酶基因及其转录调节因子的表达。与野生型菌株相比，ΔlaeA的细胞外蛋白峰值和内切葡聚糖酶活性分别增加了30.6%和5.5%。此外，全局组蛋白甲基化分析表明LaeA与调节H3K9甲基化水平有关。LaeA调节真菌生理的正常功能依赖于甲基转移酶活性。
本研究中的研究阐明了LaeA在调节真菌生长和纤维素酶生产中的功能并阐明了其调控网络，这将显著加深我们对丝状真菌中LaeA调控机制的理解，并为通过代谢工程改善工业真菌菌株的发酵特性提供新策略。
