To increase our understanding of the adaptation for copper (Cu) deficiency, Arabidopsis mutants with apparent alterations under Cu deficiency were identified. In this report, a novel mutant, tpst-2, was found to be more sensitive than wild-type (Col-0) plants to Cu deficiency during root elongation. The positional cloning of tpst-2 revealed that this gene encodes a tyrosylprotein sulfotransferase (TPST). Moreover, the ethylene production of tpst-2 mutant was higher than that of Col-0 under Cu deficiency, and adding the ethylene response inhibitor AgNO3 partially rescued defects in root elongation. Interestingly, peptide hormone phytosulfokine (PSK) treatment also repressed the ethylene production of tpst-2 mutant plants. Our results revealed that TPST suppressed ethylene production through the action of PSK.