Heterotrimeric G-Protein Signaling Is Required for Cellulose Degradation in Neurospora crassa.
Heterotrimeric G-Protein Signaling Is Required for Cellulose Degradation in Neurospora crassa.
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DOI：
10.1128/mbio.02419-20
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发表时间：
2020-11-24
期刊：
影响因子：
6.4
通讯作者：
Borkovich KA
中科院分区：
文献类型：
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作者：
Collier LA;Ghosh A;Borkovich KA
丝状真菌通过将木质纤维素生物质降解成用于代谢的更简单的化合物，对于生物圈中的植物凋落物的再循环至关重要。腐殖和病原真菌都利用植物细胞壁降解酶来释放碳进行代谢。几项研究已经证明了纤维素酶在真菌病原体感染经济相关作物期间的作用。特别是在发展中国家，严重的植物疾病意味着整个作物的损失，有时甚至导致饥饿。在这项研究中，我们证明了G蛋白信号是纤维素酶生产的关键组成部分。因此，了解G蛋白信号传导在这些生物体调节纤维素独特代谢中的作用，可以为生物燃料生产的工业相关物种的菌株工程创新以及应对植物病原体引起的粮食短缺提供信息。丝状真菌粗糙脉孢菌分解木质纤维素生物质以产生作为碳源的可溶性糖。在这项研究中，我们研究了异源三聚体G蛋白信号在纤维素降解中的作用。Gα亚基基因gna-1和gna-3、Gβ亚基基因gnb-1和cpc-2、Gγ基因gng-1或下游效应子腺苷酸环化酶（cr-1）基因的缺失导致可检测的纤维素酶活性的缺失。在表达gna-3的组成型活性形式（gna-3Q 208 L）的菌株中也观察到这种缺陷。我们发现GNA-1水平在Δgna-3、Δgnb-1和Δgng-1菌株中大大降低，可能导致这些遗传背景中的纤维素酶缺陷。尽管GNA-1蛋白水平大大降低，但gna-3Q 208 L Δgnb-1菌株表现出纤维素酶活性的观察结果与GNA-3的纤维素酶产生的阳性对照一致，这在gnb-1不存在的情况下表现出来。5个纤维素酶基因的表达模式显示Δgna-1、Δgnb-1和Δgna-3突变体比野生型产生更少的纤维素酶mRNA，这与转录调控一致。Δcpc-2突变体具有野生型水平的纤维素酶转录物，表明转录后控制。相反，Δcr-1突变体的结果支持cAMP信号对纤维素酶活性的转录和转录后控制。Δgna-3突变体中的纤维素酶活性缺陷通过cAMP补充完全修复，与GNA-3在cAMP信号传导上游操作一致。相比之下，cAMP添加仅部分校正Δgna-1和Δgnb-1突变体中的纤维素酶活性缺陷，表明GNA-1和GNB-1参与了控制纤维素酶活性的额外cAMP非依赖性途径。
Filamentous fungi are critical for the recycling of plant litter in the biosphere by degrading lignocellulosic biomass into simpler compounds for metabolism. Both saprophytic and pathogenic fungi utilize plant cell wall-degrading enzymes to liberate carbon for metabolism. Several studies have demonstrated a role for cellulase enzymes during infection of economically relevant crops by fungal pathogens. Especially in developing countries, severe plant disease means loss of entire crops, sometimes leading to starvation. In this study, we demonstrate that G-protein signaling is a key component of cellulase production. Therefore, understanding the role of G-protein signaling in the regulation of the unique metabolism of cellulose by these organisms can inform innovations in strain engineering of industrially relevant species for biofuel production and in combatting food shortages caused by plant pathogens. The filamentous fungus Neurospora crassa decomposes lignocellulosic biomass to generate soluble sugars as carbon sources. In this study, we investigated a role for heterotrimeric G-protein signaling in cellulose degradation. Loss of the Gα subunit genes gna-1 and gna-3, the Gβ subunit genes gnb-1 and cpc-2, the Gγ gene gng-1, or the gene for downstream effector adenylyl cyclase (cr-1) resulted in loss of detectable cellulase activity. This defect was also observed in strains expressing a constitutively active version of gna-3 (gna-3Q208L). We found that GNA-1 levels are greatly reduced in Δgna-3, Δgnb-1, and Δgng-1 strains, likely contributing to cellulase defects in these genetic backgrounds. The observation that gna-3Q208L Δgnb-1 strains exhibit cellulase activity, despite greatly reduced levels of GNA-1 protein, is consistent with positive control of cellulase production by GNA-3 that is manifested in the absence of gnb-1. Expression patterns for five cellulase genes showed that Δgna-1, Δgnb-1, and Δgna-3 mutants produce less cellulase mRNA than the wild type, consistent with transcriptional regulation. Δcpc-2 mutants had wild-type levels of cellulase transcripts, suggesting posttranscriptional control. In contrast, results for Δcr-1 mutants support both transcriptional and posttranscriptional control of cellulase activity by cAMP signaling. Cellulase activity defects in Δgna-3 mutants were fully remediated by cAMP supplementation, consistent with GNA-3 operating upstream of cAMP signaling. In contrast, cAMP addition only partially corrected cellulase activity defects in Δgna-1 and Δgnb-1 mutants, suggesting participation of GNA-1 and GNB-1 in additional cAMP-independent pathways that control cellulase activity.