Strigolactone-mediated inhibition of glucosinolate biosynthesis modulates parasitic plant germination in the Arabidopsis thaliana rhisosphere Choukri et al., 2025

Parasitic plants are significant agricultural threats through host-specific interactions mediated by chemical signaling metabolites. Here, we investigated the main metabolites actors underlying germination stimulation of the parasitic plant Phelipanche ramosa by Arabidopsis thaliana, focusing on the roles of glucosinolate and strigolactone pathways. Through co-germination assays, biochemical fractionation, and mutant analysis, we demonstrated that A. thaliana Col-0 seeds specifically stimulate P. ramosa germination through glucosinolate-derived metabolites rather than strigolactones. Solid-phase extraction and RP-HPLC analysis revealed that the primary bioactive compound is 4-methylsulfinylbutyl isothiocyanate (4-MSOB-NCS, sulforaphane), which eluted at 14.5 minutes and induced 29% germination. Glucosinolate-deficient mutants (gKO) completely abolished parasitic germination stimulation, while strigolactone-deficient mutants (sKO) maintained or enhanced activity, confirming the central role of the glucosinolate pathway.

Unexpectedly, we discovered that strigolactones negatively regulate glucosinolate-mediated parasite stimulation. Strigolactone-deficient lines showed increased germination potency (0.36 log10-fold increase in ED50 VS WT Col-0) and accumulated significantly higher levels of glucosinolates (1.076 pmol.mg-1 increase). This regulatory effect operated downstream of strigolactone perception through D14 and KAR HTL receptors but was phenotypically independent of MAX2, as evidenced by distinct bioactive metabolite profiles in perception mutants versus MAX2 mutants. The regulation primarily affected glucosinolate biosynthesis and potentially their hydrolysis to isothiocyanates, suggesting complex metabolic crosstalk between these pathways.

These findings confirmed a new regulatory network where strigolactones modulates indirectly plant-plant interaction chemistry, potentially representing an evolutionary trade-off between totally independent pathways. Understanding this pathway interaction provides new information into host-parasite chemical communication and may inform strategies for managing parasitic plant infestations in agriculture.