Mode-of-action of the natural herbicide radulanin A as an inhibitor of photosystem II

BACKGROUNDRadulanin A is a natural 2,5-dihydrobenzoxepin synthesized by several liverworts of the Radula genus. Breakthroughs in the total synthesis of radulanin A paved the way for the discovery of its phytotoxic activity. Nevertheless, its mode-of-action (MoA) has remained unknown so far and thus was investigated, in Arabidopsis thaliana. RESULTSRadulanin A phytotoxicity was associated with cell death and partially depended on light exposure. Photosynthesis measurements based on chlorophyll-a fluorescence evidenced that radulanin A and a Radula chromene inhibited photosynthetic electron transport with IC50 of 95 and 100 & mu;m, respectively. We established a strong correlation between inhibition of photosynthesis and phytotoxicity for a range of radulanin A analogs. Based on these data, we also determined that radulanin A phytotoxicity was abolished when the hydroxyl group was modified, and was modulated by the presence of the heterocycle and its aliphatic chain. Thermoluminescence studies highlighted that radulanin A targeted the Q(B) site of the Photosystem II (PSII) with a similar MoA as 3-(3,4-dichloropheny)-1,1-dimethylurea (DCMU). CONCLUSIONWe establish that radulanin A targets PSII, expanding Q(B) sites inhibitors to bibenzyl compounds. The identification of an easy-to-synthesize analog of radulanin A with similar MoA and efficiency might be useful for future herbicide development. & COPY; 2023 Society of Chemical Industry.

Automated summary

Radulanin A, synthesized by liverworts, exhibits phytotoxic activity by inhibiting photosynthesis and targeting the Q(B) site of Photosystem II (PSII). The findings provide insights for the development of potential herbicides.