Department of Microbiology and Plant Pathology, University of California, Riverside, Riverside, California, USA.
Graduate Program in Biochemistry and Molecular Biology, University of California, Riverside, Riverside, California, USA.
mBio. 2020 Nov 24;11(6):e02419-20. doi: 10.1128/mBio.02419-20.
The filamentous fungus 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 and , the Gβ subunit genes and , the Gγ gene , or the gene for downstream effector adenylyl cyclase () resulted in loss of detectable cellulase activity. This defect was also observed in strains expressing a constitutively active version of - ( ). We found that GNA-1 levels are greatly reduced in Δ-, Δ, and Δ strains, likely contributing to cellulase defects in these genetic backgrounds. The observation that Δ 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 Expression patterns for five cellulase genes showed that Δ, Δ, and Δ mutants produce less cellulase mRNA than the wild type, consistent with transcriptional regulation. Δ mutants had wild-type levels of cellulase transcripts, suggesting posttranscriptional control. In contrast, results for Δ mutants support both transcriptional and posttranscriptional control of cellulase activity by cAMP signaling. Cellulase activity defects in Δ 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 Δ and Δ mutants, suggesting participation of GNA-1 and GNB-1 in additional cAMP-independent pathways that control cellulase activity. 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.
丝状真菌将木质纤维素生物质分解为可溶性糖作为碳源。在这项研究中，我们研究了三聚体 G 蛋白信号在纤维素降解中的作用。缺失 Gα亚基基因、、Gβ亚基基因、、Gγ基因或下游效应物腺苷酸环化酶（）的基因导致可检测到的纤维素酶活性丧失。在表达组成型激活形式的-（）的菌株中也观察到这种缺陷。我们发现，在Δ-、Δ-和Δ-菌株中，GNA-1 水平大大降低，这可能导致这些遗传背景中纤维素酶缺陷。尽管 GNA-1 蛋白水平大大降低，但观察到Δ-菌株表现出纤维素酶活性，这与 GNA-3 对纤维素酶产生的正调控一致，这种调控在没有表达时表现出来。五个纤维素酶基因的表达模式表明，与野生型相比，Δ-、Δ-和Δ-突变体产生的纤维素酶 mRNA 较少，这与转录调控一致。Δ-突变体具有野生型水平的纤维素酶转录物，表明存在转录后调控。相比之下，Δ-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调控。cAMP 补充完全修复了Δ-突变体的纤维素酶活性缺陷，与 GNA-3 在上游作用于 cAMP 信号一致。相比之下，cAMP 的添加仅部分纠正了Δ-和Δ-突变体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其他 cAMP 独立途径。丝状真菌通过将木质纤维素生物质降解为更简单的化合物以供代谢，在生物圈中对植物凋落物的循环利用至关重要。腐生真菌和病原真菌都利用植物细胞壁降解酶来释放用于代谢的碳。几项研究表明，在真菌病原体感染经济上相关作物时，纤维素酶在其中发挥作用。特别是在发展中国家，严重的植物病害意味着整个作物的损失，有时会导致饥饿。在这项研究中，我们证明 G 蛋白信号是纤维素酶产生的关键组成部分。因此，了解 G 蛋白信号在这些生物体独特的纤维素代谢调节中的作用，可以为工业上相关物种的生物燃料生产和对抗由植物病原体引起的粮食短缺提供创新思路。
