Toxicity and Glutathione <i>S</i>‑Transferase-Catalyzed\nMetabolism of <i>R</i>‑/<i>S</i>‑Metolachlor\nin Rice

Metolachlor, the chiral herbicide,\ninhibits the very-long-chain\nfatty acid (VLCFA) synthesis; elucidating the enantioselectivity between <i>R</i>- and <i>S</i>-metolachlor in the toxicological\ndifference will facilitate the understanding of the site of action.\nWe found that the endogenous accumulation of C22 VLCFAs decreased\nin both <i>R</i>-/<i>S</i>-metolachlor -treated\nplants by 6, 12, and 24 h after treatment, with more significant reduction\nin the <i>S</i> isomer group. Gene expression of glutathione <i>S</i>-transferase <i>OsGST Tau</i> members were obviously\ninduced upon treatments with <i>S</i> or <i>R</i> isomer; both OsGSTU1 and OsGSTU4 can metabolize metolachlor effectively,\nwith <i>S</i> isomer as the preference by directly catalyzing\nthe conjugation between <i>S</i>-metolachlor and glutathione.\nIn the current study, we provide the first evidence in rice seedlings\nthat <i>S</i>-metolachlor showed herbicidal toxicity by\nblocking the synthesis of C22-type fatty acid, which eventually affects\nthe whole elongation chain of (V)LCFA. Meanwhile, OsGSTU1 and 4 metabolize\nthe metolachlor with the <i>S</i> isomer as preference.\nAll of these discoveries broaden our knowledge about metolachlor toxicology\nand enantioselectivity.