Efficient Production of Health-Beneficial Cajaninstilbene Acid in an In Situ Fermentation System Composed of Endophytic Fungus <i>Penicillium polonicum</i> R-461 and Agricultural Byproduct Pigeon Pea Roots

Cajaninstilbene acid (CSA), an important stilbene compound primarily found in pigeon pea leaves, exhibits notable health-beneficial properties. This study developed an in situ fermentation system composed of the endophytic fungus <i>Penicillium polonicum</i> (<i>P. polonicum</i>) R-461 and pigeon pea roots (PPRs) to enhance CSA production. Under the optimal conditions, <i>P. polonicum</i> R-461 efficiently converted the CSA precursors/intermediates in PPRs, achieving a 126.3-fold increase in CSA yield (37,406.51 μg/g of DW) compared to untreated PPRs (296.21 μg/g of DW). The fungus could utilize the nutrients from PPRs for growth. Additionally, <i>P. polonicum</i> R-461 was found to convert flavonoid glycosides to aglycones in PPRs. Importantly, three stilbene compounds (pinosylvin, resveratrodehyde B, and piceatannol) that had not previously been identified in pigeon peas were detected for the first time in this fermentation system. Overall, these findings highlight the potential of endophytic fungi as biocatalysis and biosynthesis platforms for the effective utilization of host substrates to produce high-value natural products.