The study identifies ALR1, a leucine-rich-repeat receptor-like kinase (LRR-RLK), as a plant aluminum (Al) ion sensor. ALR1 is located in the cytoplasmic domain and binds Al ions, which recruit the co-receptor BAK1, promoting ALR1-dependent phosphorylation of the NADPH oxidase RbohD. This enhances reactive oxygen species (ROS) generation, which oxidatively modifies the F-box protein RAE1, inhibiting its proteolytic activity and preventing the degradation of the central regulator STOP1. This leads to the activation of organic acid anion secretion, detoxifying Al. ALR1 is essential for Al resistance through an integrated signaling pathway, providing insights into ion-sensing mechanisms and enabling future molecular breeding of acid-soil-tolerant crops and trees. The findings highlight ALR1's role in Al perception and signaling, with its cytoplasmic domain responsible for Al sensing, while its extracellular domain is involved in PSK signaling. ALR1's function is dependent on STOP1, which is regulated by RAE1 and ROS. The study also shows that ALR1-mediated Al signaling is distinct from PSK signaling, with ALR1 playing a dual role in root growth and Al stress response. The discovery of ALR1 as an Al ion receptor has significant implications for improving agricultural productivity and forest restoration.The study identifies ALR1, a leucine-rich-repeat receptor-like kinase (LRR-RLK), as a plant aluminum (Al) ion sensor. ALR1 is located in the cytoplasmic domain and binds Al ions, which recruit the co-receptor BAK1, promoting ALR1-dependent phosphorylation of the NADPH oxidase RbohD. This enhances reactive oxygen species (ROS) generation, which oxidatively modifies the F-box protein RAE1, inhibiting its proteolytic activity and preventing the degradation of the central regulator STOP1. This leads to the activation of organic acid anion secretion, detoxifying Al. ALR1 is essential for Al resistance through an integrated signaling pathway, providing insights into ion-sensing mechanisms and enabling future molecular breeding of acid-soil-tolerant crops and trees. The findings highlight ALR1's role in Al perception and signaling, with its cytoplasmic domain responsible for Al sensing, while its extracellular domain is involved in PSK signaling. ALR1's function is dependent on STOP1, which is regulated by RAE1 and ROS. The study also shows that ALR1-mediated Al signaling is distinct from PSK signaling, with ALR1 playing a dual role in root growth and Al stress response. The discovery of ALR1 as an Al ion receptor has significant implications for improving agricultural productivity and forest restoration.