Pfannmüller Andreas, Boysen Jana M, Tudzynski Bettina
Molecular Biology and Biotechnology of Fungi, Department of Biology, Institute of Biology and Biotechnology of Plants, University of Münster Münster, Germany.
Front Microbiol. 2017 Mar 14;8:381. doi: 10.3389/fmicb.2017.00381. eCollection 2017.
Secondary metabolite production of the phytopathogenic ascomycete fungus is greatly influenced by the availability of nitrogen. While favored nitrogen sources such as glutamine and ammonium are used preferentially, the uptake and utilization of nitrate is subject to a regulatory mechanism called nitrogen metabolite repression (NMR). In , the transcriptional control of the nitrate assimilatory system is carried out by the synergistic action of the nitrate-specific transcription factor NirA and the major nitrogen-responsive regulator AreA. In this study, we identified the main components of the nitrate assimilation system in and studied the role of each of them regarding the regulation of the remaining components. We analyzed mutants with deletions of the nitrate-specific activator NirA, the nitrate reductase (NR), the nitrite reductase (NiR) and the nitrate transporter NrtA. We show that NirA controls the transcription of the nitrate assimilatory genes , , and in the presence of nitrate, and that the global nitrogen regulator AreA is obligatory for expression of most, but not all NirA target genes (). By transforming a NirA-GFP fusion construct into the Δ, Δ, and Δ mutant backgrounds we revealed that NirA was dispersed in the cytosol when grown in the presence of glutamine, but rapidly sorted to the nucleus when nitrate was added. Interestingly, the rapid and nitrate-induced nuclear translocation of NirA was observed also in the Δ and Δ mutants, but not in Δ, suggesting that the fungus is able to directly sense nitrate in an AreA- and NrtA-independent, but NR-dependent manner.
植物病原子囊菌真菌的次级代谢产物合成受到氮可用性的极大影响。虽然优先使用谷氨酰胺和铵等优质氮源，但硝酸盐的吸收和利用受到一种称为氮代谢物阻遏（NMR）的调控机制的制约。在[具体物种]中，硝酸盐同化系统的转录控制是由硝酸盐特异性转录因子NirA和主要的氮响应调节因子AreA协同作用来进行的。在本研究中，我们鉴定了[具体物种]中硝酸盐同化系统的主要成分，并研究了它们各自在调控其余成分方面的作用。我们分析了硝酸盐特异性激活因子NirA、硝酸还原酶（NR）、亚硝酸还原酶（NiR）和硝酸盐转运蛋白NrtA缺失的突变体。我们发现，在有硝酸盐存在的情况下，NirA控制硝酸盐同化基因[具体基因名称1]、[具体基因名称2]和[具体基因名称3]的转录，并且全局氮调节因子AreA对于大多数（但不是全部）NirA靶基因的表达是必需的（[相关说明]）。通过将NirA-GFP融合构建体转化到Δ[相关基因名称1]、Δ[相关基因名称2]和Δ[相关基因名称3]突变体背景中，我们发现当在谷氨酰胺存在下生长时，NirA分散在细胞质中，但添加硝酸盐后会迅速分选到细胞核中。有趣的是，在Δ[相关基因名称1]和Δ[相关基因名称2]突变体中也观察到了NirA由硝酸盐诱导的快速核转位，但在Δ[相关基因名称3]中未观察到，这表明该真菌能够以一种不依赖AreA和NrtA，但依赖NR的方式直接感知硝酸盐。
