Extracellular melanin from Paecilomyces variotii improves sorghum development and seed formation under salt stress

Salt stress severely limits sorghum growth and productivity. Previously, we isolated a fungal strain, Paecilomyces variotii , and found that its fermentation broth significantly enhanced the salt tolerance of sorghum. In this study, we further isolated a melanin compound, PVME, from its metabolites and elucidated its mechanism of regulating sorghum growth and development under salt stress. The results revealed that PVME treatment significantly alleviated the inhibition caused by salt stress, as evidenced by increased plant height, improved root development, and higher chlorophyll content. In addition, PVME promoted the accumulation of compatible solutes, enhanced antioxidant enzyme activities, and maintained Na + /K + ion homeostasis. Integrated transcriptomic and metabolomic analyses further revealed that PVME activated the phenylpropanoid and flavonoid biosynthesis pathways. These coordinated responses contributed to improved plant growth from the vegetative stage to heading stage and promoted seed development under saline conditions. In conclusion, the extracellular melanin PVME derived from Paecilomyces variotii effectively promotes the growth and development of sorghum under salt stress by enhancing antioxidant capacity, maintaining ion homeostasis, and stimulating secondary metabolism. This study highlights the potential of fungal secondary metabolites for improving crop salt tolerance and supports their application in sustainable agriculture.