Spermidine Regulates Mitochondrial Function by Enhancing eIF5A Hypusination and Contributes to Reactive Oxygen Species Production and Ganoderic Acids Biosynthesis in Ganoderma lucidum

Spermidine, a kind of polycation and one important member in the polyamine family, is essential for survival in many kinds of organisms and participates in the regulation of cell growth and metabolism. To explore the mechanism by which spermidine regulates ganoderic acids (GAs) biosynthesis in Ganoderma lucidum , the effects of spermidine on GAs and reactive oxygen species (ROS) contents were examined. Our data suggested that spermidine promoted the production of mitochondrial ROS and positively regulated GAs biosynthesis. Further research revealed that spermidine promoted the translation of mitochondrial complexes I and II and subsequently influenced their activity. With the reduction in eukaryotic translation initiation factor 5A (eIF5A) hypusination by over 50% in spermidine synthase gene ( spds ) knockdown strains, the activity of mitochondrial complexes I and II was reduced by nearly 60% and 80%, respectively, and the protein content was reduced by over 50%, suggesting that the effect of spermidine in mitochondrial complexes I and II was mediated through its influence on eIF5A hypusination. Furthermore, after knocking down eIF5A , the deoxyhypusine synthase gene ( dhs ) and the deoxyhypusine hydroxylase gene ( dohh ), mitochondrial ROS level was reduced by nearly 50%, and GAs content was reduced by over 40%, suggesting that eIF5A hypusination contributed to mitochondrial ROS production and GAs biosynthesis. In summary, spermidine maintains mitochondrial ROS homeostasis by regulating the translation and subsequent activity of complexes I and II via eIF5A hypusination and promotes GAs biosynthesis via mitochondrial ROS signaling. The present findings provide new insight into spermidine-mediated biosynthesis of secondary metabolites. IMPORTANCE: Spermidine is necessary for organism survival and is involved in the regulation of various biological processes. However, the specific mechanisms underlying the various physiological functions of spermidine are poorly understood, especially in microorganisms. In this study, we found that spermidine hypusinates eIF5A to promote the production of mitochondrial ROS and subsequently regulate secondary metabolism in microorganisms. Our study provides a better understanding of the mechanism by which spermidine regulates mitochondrial function and provides new insight into spermidine-mediated biosynthesis of secondary metabolites.