The RAE1-STOP1 Module Reduces Sensitivity to Exogenous ABA Treatment by Regulating ABI5 in Arabidopsis

The SENSITIVE TO PROTON RHIZOTOXICITY 1 (STOP1) transcription factor plays a pivotal role in maintaining cellular ion balance and governing aluminum tolerance in plants. Abscisic acid (ABA) participates in aluminum tolerance by inducing the expression of several genes that are STOP1 targets. However, the mechanisms underlying ABA signaling and STOP1-mediated gene expression remain poorly understood. The F-box protein RAE1, an SCF-type E3 ligase component, recognizes STOP1 and controls its ubiquitination and degradation. This study revealed that exogenous ABA supplementation reduced STOP1 levels by promoting the expression of RAE1. Notably, both RAE1 loss-of-function mutants and STOP1 overexpressing lines showed enhanced sensitivity to exogenous ABA treatment, which correlated with early stage post-transcriptional upregulation of ABSCISIC ACID INSENSITIVE5 (ABI5). Our observations strongly suggest that RAE1 operates as an ABA-responsive factor, exerting control over STOP1 homeostasis, and thus establishing a negative feedback loop that controls ABA responses in Arabidopsis. Thus, our study revealed a novel function of the RAE1-STOP1 module in ABA signaling, highlighting its role in reducing ABA sensitivity by preventing ABI5 increase. Single Sentence SummaryF-box protein RAE1 functions as an exogenous ABA responsive mediator to reduce STOP1-mediated ABA sensitivity.