Effects of Exogenous Phenolic Acids on Haustorium Induction of Cistanche deserticola Seeds Based on Host Metabolome Data

<i>Cistanche deserticola</i>, a holoparasitic plant widely used in traditional Chinese medicine, relies on chemical signals from its host plant, <i>Haloxylon ammodendron</i>, to initiate seed germination and haustorium induction. This study employed UPLC-MS/MS to analyze the root metabolites of <i>H. ammodendron</i>. The results showed that 11 substances such as phenolic acids, flavonoids, and alkaloids were mainly contained in the roots of <i>H. ammodendron</i>, among which phenolic acids accounted for the largest proportion, accounting for 18.00% in winter samples and 16.11% in autumn samples. Based on the reported exogenous substances that promote haustorium induction in <i>C. deserticola</i> and the differential metabolites in <i>H. ammodendron</i> roots, we selected seven exogenous signaling substances: 2,6-dimethoxy-1,4-benzoquinone, resorcinol, ferulic acid, syringic acid, vanillic acid, vanillin, and pelargonidin. Through concentration-gradient experiments (0.1-100 μM), we assessed their effects on haustorium induction in <i>C. deserticola</i> seeds. The results showed that among the seven substances, syringic acid, vanillic acid, and vanillin had the best impact on promoting the haustorium induction of <i>C. deserticola</i> seeds. Vanillic acid had the best impact at the concentration of 10 μmol/L, and the highest haustorium induction rate was 50.2%. There was no significant difference in the concentrations of vanillin and syringic acid. The results showed that phenolic acids in the host root system stimulated haustoria induction in <i>C. deserticola</i> seeds, with different substances requiring different optimal concentrations. This study not only identifies specific phenolic acids that enhance <i>C. deserticola</i> productivity but also establishes a chemical ecology framework for investigating host-parasite interactions in other root parasitic species.