A cross-kingdom metabolite signal: tryptophan from Bacillus amyloliquefaciens triggers Ophiocordyceps sinensis morphogenesis via the TOR-BRG1 pathway

The development of the Chinese cordyceps relies on the efficient transformation of blastospores to hyphae of the high-value medicinal fungus Ophiocordyceps sinensis , which occurs in the hemolymph of Thitarodes . While host-associated microbiota are thought to facilitate this process in nature, the fundamental processes involved are still unclear. We identified the host associated bacterium Bacillus amyloliquefaciens as a potent microbial symbiont that dramatically enhances the blastospore-to-hypha transition in O. sinensis , increasing its transformation rate from 23.2 to 58.8% at day 8. Through a combination of bioassays, transcriptomics, and functional validation, we delineate a novel cross-kingdom signaling pathway underlying this phenomenon. Our transcriptomic analysis revealed that the B. amyloliquefaciens supernatant triggers extensive transcriptional reprogramming in the O. sinensis , upregulating the TOR signaling pathway and the key transcription factor involved in spore–hyphae transformation, including BRG1 . Functional studies confirmed that bacterial-derived tryptophan is the key signaling metabolite modulating this TOR- BRG1 regulatory axis. The expression of hypha-specific genes and critical cell wall remodeling enzymes (Chitin Synthase 2 and 3, Hyphal Wall Protein 1, agglutinin-like sequence 3 protein, and β-1,3-glucan synthase) were also upregulated. Our findings elucidate a previously unknown bacterial-fungal communication mechanism in which a B. amyloliquefaciens tryptophan directly regulates O. sinensis development by activating a conserved TOR- BRG1 morphogenetic pathway. This presents a transformative biological strategy to overcome a major bottleneck in the sustainable production of Chinese cordyceps.