Metacycloprodigiosin from Rhizosphere Streptomyces aurantiacus as a Natural Antifungal Agent against Fusarium oxysporum.

Microbiome-guided crop protection increasingly emphasizes the chemical basis of disease suppression. Here, we identify Streptomyces aurantiacus YS-4, a rhizosphere-enriched actinobacterium selectively recruited by resistant cultivars of Salvia miltiorrhiza, as a producer of metacycloprodigiosin, a previously reported secondary metabolite that is reported for the first time in this strain and further investigated for its role in suppressing Fusarium oxysporum-induced root rot in S. miltiorrhiza. Metacycloprodigiosin inhibited Fusarium oxysporum growth by 81.66% at 200 μg mL-1 and induced extensive cellular and transcriptional changes related to membrane function and virulence-associated pathways. Transmission electron microscopy confirmed severe hyphal damage, while transcriptomic profiling revealed broad downregulation of virulence-associated genes. Pot experiments demonstrated that YS-4 application alleviated root rot symptoms and enhanced plant biomass. Collectively, these findings establish a direct link between metabolite chemistry and pathogen suppression, advancing molecular understanding of plant-fungal interactions and highlighting metacycloprodigiosin as a promising biocontrol agent for sustainable management of crops.