ABCG transporters are involved in the accumulation of specialized metabolites in the oil bodies of Marchantia polymorpha

Abstract

Bioactive specialized metabolites (SMs) are synthesized and sequestered in specific cellular compartments or organelles as a self-defense strategy against their intrinsic toxicity. Liverwort-specific oil bodies accumulate large amounts of SMs and contribute to chemical defense; however, the molecular mechanisms underlying SM sequestration in oil bodies remain largely unknown. Therefore, in this study, we focused on MpABCG1 and MpABCG36, which are ATP-binding cassette (ABC) protein family members localized to the oil bodies of liverwort Marchantia polymorpha. Sesquiterpene (thujopsene, chamigrene, and himachalane) accumulation was reduced in the Mpabcg1 and Mpabcg36 loss-of-function mutants. Notably, levels of the bisbibenzyls, marchantins C and A, were predominantly reduced in Mpabcg1, but not in Mpabcg36. Although the Mpabcg1 mutant formed a number of oil bodies labeled with mCitrine- MpSYP12B (oil body membrane marker) comparable to that of the wild-type, the number of oil bodies stained with BODIPY 493/503, which has an affinity for lipophilic SMs, was reduced. This finding suggests that MpABCG1 and MpABCG36 mutations affect SM accumulation in the oil body but have little impact on oil body formation. Overall, our results highlight the involvement of MpABCG1 and MpABCG36 in the accumulation of SMs and/or their precursors in liverwort oil bodies.