Arsenic-sensing domain controls ACR3 transporter trafficking in Marchantia polymorpha.

Arsenic is a toxic, carcinogenic metalloid that threatens human health through contaminated water and food. Arsenite [As(III)] efflux mediated by ACR3 transporters is an ancient detoxification mechanism conserved across prokaryotes, fungi, algae, and non-angiosperm land plants, yet plant ACR3 proteins remain poorly characterized. Here, we show that MpACR3, the ACR3 ortholog from the model liverwort Marchantia polymorpha, contains an arsenic-responsive N-terminal domain that regulates intracellular trafficking. Under nonstress conditions, MpACR3 is detected in Golgi bodies as well as at the plasma membrane (PM) in plant cells, whereas As(III) promotes its relocalization to the PM. As(III) interacts with a cysteine-rich N-terminal region and stabilizes this domain, as shown by arsenite-biotin competition and increased protease resistance. Together with molecular dynamics simulations, which predict As(III)-dependent changes in secondary structure and surface properties, these findings support a model in which ligand-induced remodeling of the N-terminus modulates MpACR3 retention and trafficking. We further identify a di-arginine-containing LRCRF motif in which leucine and arginine residues are required for intracellular retention, whereas cysteine and phenylalanine residues are required for As(III)-induced relocalization to the PM. The broad conservation of related N-terminal domains in plant ACR3 transporters suggests that arsenic-regulated trafficking is a conserved plant adaptation to arsenic toxicity.