PlSIRP1 Activates PlABI5 via Dual Mechanisms to Repress PlPIP2;1 and Maintain ABA‐Mediated Seed Dormancy in Paeonia lactiflora

ABSTRACT

Seed dormancy is a critical adaptive trait that ensures seedling establishment under favourable conditions. Paeonia lactiflora seeds exhibit dual hypocotyl and epicotyl dormancy, severely limiting large‐scale propagation. Although abscisic acid (ABA) is the central hormone governing dormancy, the molecular mechanisms linking ABA signalling to seed water status remain elusive. Here, we identified that the RING‐H2 E3 ubiquitin ligase PlSIRP1 acts as a positive regulator of ABA‐mediated seed dormancy in P. lactiflora . PlSIRP1 expression was induced by ABA and peaked during deep dormancy. Mechanistically, PlSIRP1 promoted dormancy through dual nondegradative mechanisms: it directly bound and activated the PlABI5 promoter, while concurrently interacting with PlABI5 in the nucleus to enhance its DNA‐binding and transcriptional repression activities without triggering PlABI5 ubiquitination or altering its stability. We further demonstrated the aquaporin PlPIP2;1 as a direct downstream target; PlABI5 repressed PlPIP2;1 transcription to restrict seed water uptake and hypocotyl elongation. Genetic and transgenic analyses established that PlSIRP1 functions upstream of PlABI5 to maintain dormancy, a regulatory hierarchy conserved in Arabidopsis thaliana . Collectively, our findings establish the PlSIRP1‐PlABI5‐ PlPIP2;1 signalling module and reveal a nondegradative paradigm by which an E3 ubiquitin ligase couples ABA signalling to aquaporin‐mediated water transport. These results provide molecular insights into ABA‐dependent dormancy regulation in perennial plants and suggest potential strategies for alleviating seed dormancy to improve propagation efficiency.