Floral development in Paeonia suffruticosa ‘Doulv’ and functional characterization of the PsSEP1L

Tree peony ( Paeonia section Moutan DC.) is of great ornamental value because of its diverse flower types; however, the molecular mechanisms governing its floral morphogenesis remain poorly understood. In this study, ‘Doulv’, a cultivar prized for its double-flowered phenotype, was investigated. Morphological and histological analyses documented a progressive increase in petal number during floral development. Transcriptomic profiling identifies PsSEP1L , an E-class MADS-box gene, as a candidate regulator, with elevated expression during petal development and distinct expression patterns across floral organs. Functional validation through transient overexpression and virus-induced gene silencing demonstrates that PsSEP1L positively regulates petal number. Yeast two-hybrid and Bimolecular fluorescence complementation assays show that PsSEP1L interacts with PsSEP3, PsAP3, and PsAG, and expression analyses of these interactors in transiently transformed tissues suggest a cooperative regulatory network controlling floral morphology. Collectively, these findings elucidate a key molecular module underlying petal proliferation, providing a theoretical basis for molecular breeding of tree peony cultivars.