Identification of Amino Acid Residues Important for the Arsenic Resistance Function of Arabidopsis ABCC1

The Arabidopsis ATP-Binding Cassette (ABC) transporter ABCC1 sequesters arsenic (As)-phytochelatin conjugates into the vacuole, thereby conferring As resistance. Here, we report the results of a screen for phosphorylation-dependent regulation sites of AtABCC1. Variants of AtABCC1 harboring mutations that replaced amino acid residues Tyr(682), Tyr(709), Tyr(822), Ser(846), Ser(1278), or Thr(1408) with alanine confer reduced resistance and decrease the intracellular As content relative to wild-type AtABCC1 when heterologously expressed in the SM7 yeast strain. This suggests that these mutations compromise the vacuolar sequestration of As by AtABCC1. Furthermore, through a phosphomimic mutant study, we found that phosphorylation of Ser(846) is required for the As resistance function of AtABCC1. Our analysis provides a first clue as to the phosphorylation-mediated regulation of AtABCC1 activity.