Chloroplast vesiculation fine-tunes seed germination by antagonizing ABA signaling through dual degradation of ABI5 and XIW1

SUMMARY Abscisic acid (ABA) plays a crucial role in enforcing seed dormancy and suppressing germination under stress conditions by stabilizing key transcriptional repressors. However, the mechanisms by which plants actively attenuate this repression to resume developmental growth remain largely unclear. In this study, we identify chloroplast vesiculation (CV) as a negative regulator of ABA signaling in Arabidopsis. Silencing of CV resulted in hypersensitivity to ABA during seed germination and stomatal closure, whereas its overexpression conferred ABA insensitivity. We demonstrate that CV physically interacts with and directly promotes the vacuolar degradation of two key positive regulators of ABA signaling—the transcription factor ABI5 and the WD40-repeat protein XIW1. Genetic epistasis analyses confirmed that ABI5 and XIW1 function downstream of CV, as loss-of-function mutations in either ABI5 or XIW1 suppressed the ABA-hypersensitive phenotype of CV-silenced plants. Furthermore, we found that ABA itself negatively regulates CV at both the transcriptional and post-translational levels, forming a feedback loop that fine-tunes ABA sensitivity. Our study thus uncovers a previously unknown regulatory module in which CV attenuates ABA responses by targeting ABI5 and XIW1 for vacuolar degradation, thereby facilitating the transition from seed dormancy to germination.