Identification of Genes Involved in the Synthesis of the Fungal Cell Wall Component Nigeran and Regulation of Its Polymerization in Aspergillus luchuensis
Identification of Genes Involved in the Synthesis of the Fungal Cell Wall Component Nigeran and Regulation of Its Polymerization in Aspergillus luchuensis
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DOI：
10.1128/aem.01144-21
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发表时间：
2021-08
影响因子：
4.4
通讯作者：
K. Uechi;H. Yaguchi;Jikian Tokashiki;T. Taira;O. Mizutani
中科院分区：
文献类型：
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作者：
K. Uechi;H. Yaguchi;Jikian Tokashiki;T. Taira;O. Mizutani
真菌细胞壁主要由多糖组成。在无氮条件下，一些曲霉属和青霉属。产生显著水平的尼日利亚多糖，一种由交替的α-1，3/1，4-糖苷键组成的真菌细胞壁多糖。某些曲霉属和青霉属。在氮饥饿下产生真菌细胞壁组分尼日利亚聚糖，一种具有交替的α-1，3-和α-1，4-葡糖苷键的无支链D-葡聚糖。尼日利亚多糖生物合成的机制和尼日利亚多糖在真菌生存中的生理作用尚不清楚。我们使用RNA测序（RNA-seq）来鉴定丝状真菌曲霉luchuensis在无氮条件下生长时参与尼日利亚烷合成的基因。在氮饥饿条件下，编码α-1，3-葡聚糖合酶的agsB和两个相邻基因（agtC和gnsA）表达上调。A中agsB的破坏。luchuensis（ΔagsB）导致尼日利亚合成的完全丧失。此外，agsB在不能产生黑色素的曲霉菌株中的过表达导致了黑色素的合成。这些结果表明，agsB编码的尼日利亚合成酶。因此，我们重新命名了A。luchuensis agsB基因和nigeran synthase基因（nisA）。与野生型菌株相比，agtC突变体（ΔagtC）中的葡聚糖合成增加至121%;相反，ΔgnsA和ΔagtC ΔgnsA菌株中的葡聚糖合成分别降低至64%和63%。我们的研究结果表明，AgtC和GnsA起着重要的作用，不仅调节尼日利亚的数量，但它的聚合。总的来说，我们的结果表明nisA（agsB）在A. luchuensis，而agtC和gnsA有助于调节尼日利亚的合成和聚合。这项研究提供了深入了解真菌细胞壁的生物合成，特别是真菌α-葡聚糖合成酶基因的分子进化和尼日利亚作为一种新型生物聚合物的潜在利用。真菌的细胞壁主要由多糖组成。在无氮条件下，一些曲霉属和青霉属。产生显著水平的尼日利亚多糖，一种由交替的α-1，3/1，4-糖苷键组成的真菌细胞壁多糖。调节尼日利亚人的生物合成和功能的机制是未知的。在此，我们对无氮或低氮条件下培养的芦丘曲霉进行了RNA测序。一个假定的α-1，3-葡聚糖合酶基因，其转录水平在无氮条件下上调，被证明编码尼日利亚合酶。此外，两个基因编码的α-葡聚糖转移酶和一个假设的蛋白质被证明参与控制尼日利亚的含量和分子量。这项研究揭示了一种潜在的生物聚合物尼日利亚烷的合成相关基因，并提供了对真菌细胞壁生物合成的更深入了解。
The fungal cell wall is composed mainly of polysaccharides. Under nitrogen-free conditions, some Aspergillus and Penicillium spp. produce significant levels of nigeran, a fungal cell wall polysaccharide composed of alternating α-1,3/1,4-glucosidic linkages. ABSTRACT Certain Aspergillus and Penicillium spp. produce the fungal cell wall component nigeran, an unbranched d-glucan with alternating α-1,3- and α-1,4-glucoside linkages, under nitrogen starvation. The mechanism underlying nigeran biosynthesis and the physiological role of nigeran in fungal survival are not clear. We used RNA sequencing (RNA-seq) to identify genes involved in nigeran synthesis in the filamentous fungus Aspergillus luchuensis when grown under nitrogen-free conditions. agsB, which encodes a putative α-1,3-glucan synthase, and two adjacent genes (agtC and gnsA) were upregulated under conditions of nitrogen starvation. Disruption of agsB in A. luchuensis (ΔagsB) resulted in the complete loss of nigeran synthesis. Furthermore, the overexpression of agsB in an Aspergillus oryzae strain that cannot produce nigeran resulted in nigeran synthesis. These results indicated that agsB encodes a nigeran synthase. Therefore, we have renamed the A. luchuensis agsB gene the nigeran synthase gene (nisA). Nigeran synthesis in an agtC mutant (ΔagtC) increased to 121%; conversely, those in the ΔgnsA and ΔagtC ΔgnsA strains decreased to 64% and 63%, respectively, compared to that in the wild-type strain. Our results revealed that AgtC and GnsA play an important role in regulating not only the quantity of nigeran but also its polymerization. Collectively, our results demonstrated that nisA (agsB) is essential for nigeran synthesis in A. luchuensis, whereas agtC and gnsA contribute to the regulation of nigeran synthesis and its polymerization. This research provides insights into fungal cell wall biosynthesis, specifically the molecular evolution of fungal α-glucan synthase genes and the potential utilization of nigeran as a novel biopolymer. IMPORTANCE The fungal cell wall is composed mainly of polysaccharides. Under nitrogen-free conditions, some Aspergillus and Penicillium spp. produce significant levels of nigeran, a fungal cell wall polysaccharide composed of alternating α-1,3/1,4-glucosidic linkages. The mechanisms regulating the biosynthesis and function of nigeran are unknown. Here, we performed RNA sequencing of Aspergillus luchuensis cultured under nitrogen-free or low-nitrogen conditions. A putative α-1,3-glucan synthase gene, whose transcriptional level was upregulated under nitrogen-free conditions, was demonstrated to encode nigeran synthase. Furthermore, two genes encoding an α-glucanotransferase and a hypothetical protein were shown to be involved in controlling the nigeran content and molecular weight. This study reveals genes involved in the synthesis of nigeran, a potential biopolymer, and provides a deeper understanding of fungal cell wall biosynthesis.