Antitumor astins originate from the fungal endophyte Cyanodermella asteris living within the medicinal plant Aster tataricus

Significance Astins are natural products that bind to a crucial human regulatory protein, the stimulator of interferon genes (STING), which is a promising new therapeutic target for cancer and immune disorders. Astins have long been regarded as phytochemicals of a Chinese medicinal plant. Here, we show that they are produced by the newly identified fungal endophyte Cyanodermella asteris via a nonribosomal biosynthetic pathway. Moreover, we provide evidence that key astin variants are produced during symbiosis with the aster plant. The production of specific phytochemical variants during symbiotic interactions is poorly studied and might be more widespread than previously expected. These findings pave the way for a cost-effective biotechnological astin production.