Leibniz Institute of Plant Genetics and Crop Plant Research, Corrensstr. 3, D-06466 Gatersleben, Germany.
Fungal Genet Biol. 2012 Apr;49(4):313-21. doi: 10.1016/j.fgb.2012.02.002. Epub 2012 Feb 16.
Fumarate reductase is a protein involved in the maintenance of redox balance during oxygen deficiency. This enzyme irreversibly catalyzes the reduction of fumarate to succinate and requires flavin cofactors as electron donors. Two examples are the soluble mitochondrial and the cytosolic fumarate reductases of Saccharomyces cerevisiae encoded by the OSM1 and FRDS1 genes, respectively. This work reports the identification and characterization of the gene encoding cytosolic fumarate reductase enzyme in the arbuscular mycorrhizal fungus, Glomus intraradices and the establishment of its physiological role. Using a yeast expression system, we demonstrate that G. intraradices GiFRD encodes a protein that has fumarate reductase activity which can functionally substitute for the S. cerevisiae fumarate reductases. Additionally, we showed that GiFRD transformants are not affected by presence of salt in medium, indicating that the presence of this gene has no effect on yeast behavior under osmotic stress. The fact that GiFRD expression and enzymatic activity was present only in asymbiotic stage confirmed existence of at least one anaerobic metabolic pathway in this phase of fungus life cycle. This suggests that the AMF behave as facultative anaerobes in the asymbiotic stage.
延胡索酸还原酶是一种在缺氧时维持氧化还原平衡的蛋白质。该酶不可逆地催化延胡索酸还原为琥珀酸，并需要黄素辅因子作为电子供体。两个例子是分别由 OSM1 和 FRDS1 基因编码的酿酒酵母的可溶性线粒体和胞质延胡索酸还原酶。本工作报道了丛枝菌根真菌根内球囊霉胞质延胡索酸还原酶酶编码基因的鉴定和特征，并建立了其生理作用。使用酵母表达系统，我们证明了 G. intraradices GiFRD 编码的蛋白具有延胡索酸还原酶活性，可替代酿酒酵母的延胡索酸还原酶。此外，我们表明 GiFRD 转化体不受培养基中盐存在的影响，这表明该基因的存在对酵母在渗透胁迫下的行为没有影响。只有在非共生阶段才存在 GiFRD 表达和酶活性的事实证实了真菌生命周期的这个阶段至少存在一条厌氧代谢途径。这表明 AMF 在非共生阶段表现为兼性厌氧菌。
