The STOP1-MATE-Citrate Axis Confers Inorganic Sn Tolerance in Plants

Inorganic tin (Sn) is an emerging pollutant whose phytotoxicity and plant detoxification mechanisms remain poorly understood. Here, we demonstrate that inorganic Sn severely inhibits root growth and triggers ROS accumulation in Lemna minor and Arabidopsis. We identified the transcription factor STOP1 as a critical regulator of Sn tolerance. Mechanistically, STOP1 confers Sn tolerance primarily by activating the citrate transporter MATE, contrasting sharply with Al tolerance which relies heavily on the malate transporter ALMT1. Inorganic Sn stress strongly induced root citrate exudation, and the mate mutant displayed severe Sn hypersensitivity. Exogenous citrate application effectively rescued root growth by impeding Sn uptake and attenuating ROS overaccumulation. Our study reveals that the STOP1-MATE-citrate axis constitutes a pivotal detoxification mechanism against inorganic Sn, providing novel insights into how plants adapt to heavy metal stress through distinct organic acid secretion pathways.