背景:关于与纤维素酶生物合成相关的调节网络的知识是利用这种调节系统以低成本提高纤维素酶生产的先决条件。丝状真菌内含子滞留(IR)和无义介导的mRNA衰变(NMD)的生物学功能缺乏研究,更不用说它们在纤维素酶生物合成中的作用了。
结果:我们发现主要的纤维素酶基因(cel7a,cel7b,和cel3a)在纤维素酶生产条件下(纤维素和乳糖),伴随着更活跃的NMD途径,与纤维素酶不产生条件(葡萄糖)相比。在存在成功抑制NMD途径的NMD途径抑制剂的情况下,纤维素酶基因的mRNA水平急剧下调,但这些基因的IR率显著上调。始终如一,纤维素酶活性受到严重抑制。此外,NMD通路抑制剂引起雷帕霉素(TOR)通路两个重要靶基因的mRNA水平下调,trfkbp12和trTOR1。基因trfkbp12的缺失使得里氏木霉中的纤维素酶产生对NMD途径抑制剂更敏感。
结论:所有这些发现表明,纤维素酶基因的IR通过与NMD途径偶联来调节其自身的基因表达,这可能涉及到TOR通路。我们的结果提供了对内含子保留的更好理解,NMD途径,和丝状真菌中纤维素酶的产生机制。
BACKGROUND: Knowledge on regulatory networks associated with cellulase biosynthesis is prerequisite for exploitation of such regulatory systems in enhancing cellulase production with low cost. The biological functions of intron retention (IR) and nonsense-mediated mRNA decay (
NMD) in filamentous fungi is lack of study, let alone their roles in cellulase biosynthesis.
RESULTS: We found that major cellulase genes (cel7a, cel7b, and cel3a) exhibited concomitant decrease in IR rates and increase in their gene expression in T. reesei under cellulase-producing condition (cellulose and lactose) that was accompanied with a more active
NMD pathway, as compared to cellulase non-producing condition (glucose). In the presence of the
NMD pathway inhibitor that successfully repressed the
NMD pathway, the mRNA levels of cellulase genes were sharply down-regulated, but the rates of IR in these genes were significantly up-regulated. Consistently, the cellulase activities were severely inhibited. In addition, the
NMD pathway inhibitor caused the downregulated mRNA levels of two important genes of the target of rapamycin (TOR) pathway, trfkbp12 and trTOR1. The absence of gene trfkbp12 made the cellulase production in T. reesei more sensitive to the NMD pathway inhibitor.
CONCLUSIONS: All these findings suggest that the IR of cellulase genes regulates their own gene expression by coupling with the NMD pathway, which might involve the TOR pathway. Our results provide better understanding on intron retention, the
NMD pathway, and cellulase production mechanism in filamentous fungi.