Objective Dried flower buds or newly opened flowers of Lonicera macranthoides are used as Shanyinhua (Lonicerae Flos) for medicinal purposes. The Xianglei cultivar, developed from a natural mutant, exhibits a distinctive phenotype characterized by non-opening corolla and prolonged bud stage. Aiming to elucidate the cellular and molecular mechanisms underlying this unique corolla phenotype. Methods The flower of conventional cultivar (WT) and the Xianglei cultivar (XL) of L. macranthoides were used as materials. Corolla adaxial epidermal cells and longitudinal sections were observed using light microscopy. The expression patterns of xyloglucan endotransglucosylase/hydrolase genes (LmXTH6, LmXTH7, LmXTH33), expansin gene (LmEXP7), and pectin methylesterase genes (LmPME28, LmPME45) were analyzed by qRT-PCR. Protein-protein interaction networks were predicted using the STRING database. Ruthenium red staining coupled with Image J quantitative analysis was performed to assess the degree of pectin de-methylesterification in corolla cell walls. Results In the WT, the adaxial cells of corolla displayed a spatially sequential expansion, with the basal cells expanding first, followed by the middle cells. Moreover, the expansion rate of the adaxial cells is higher than that of the abaxial cells. In contrast, the expansion rate of the adaxial cells is significantly decreased in Xianglei, and the extend of cell expansion is not evident. Molecular analyses revealed that LmXTH6, LmXTH7, and LmXTH33 were highly expressed during the pre-anthesis and anthesis stages in WT, but were significantly suppressed in Xianglei. Expression of LmEXP7 peaked just before corolla opening in WT but remained low in Xianglei at the same stage. Furthermore, ruthenium staining showed a higher overall degree of pectin de-methylesterification in Xianglei compared with WT, which is consistent with the expressin patterns of LmPME28 and LmPME45. Conclusion The non-opening of the corolla in the L. macranthoides cultivar Xianglei is closely associated with inhibited expansion of corolla cells. The low expression of XTHs and EXP collectively contributes to the reduced expansion capacity of corolla cells in Xianglei, while the up-regulation of PMEs increases pectin de-methylesterification in the cell wall, potentially enhancing cell wall stiffness. The synergistic effect of XTH/EXP and PME may be an important factor leading to corolla non-opening in Xianglei. These findings provide experimental evidence for understanding the regulatory mechanisms underlying the superior phenotype of the Xianglei cultivar and offer new insights into the cell wall regulatory mechanisms governing floral organ morphogenesis in plants.

Lonicera macranthoides Hand.-Mazz.  /  corolla movement  /  cell wall  /  xyloglucan endotransglucosylase/hydrolase  /  expansin  /  pectin methylesterase