Weeping species are used both as ornamental plants and for breeding dwarf plant types. However, exploration of casual genes controlling weeping traits is rather limited. Here, we identified individuals with contrasting phenotypes from an F1 bi-parental mapping population of Prunus mume which was developed from a cross between the upright cultivar ‘Liuban’ and the weeping cultivar ‘Fentai Chuizhi’. Bulked segregant RNA sequencing was used and five QTLs on Chromosome 7 were identified. The Pm024074(PmUGT72B3) allele, belonging to the UDP-glycosyltransferase superfamily containing the coniferyl-alcohol glucosyltransferase domain, was identified in a genomic region overlapping with a previously identified QTL, and had a synonymous transition of T66(upright) to C (weeping) in the coding sequence and a 470-bp deletion in the promoter region. Pm024074 had exceptionally high expression in buds and stems of weeping P. mume. Weighted correlation network analysis indicates that genes neighboring Pm024074 were significantly associated with plant architecture. In addition, a reliable single nucleotide polymorphism marker was developed based on the variation in the Pm024074 gene, providing precise marker-assisted breeding for weeping traits. This study provides insights into the genetic mechanism governing the weeping trait in P. mume, and indicates potential applications for the manipulation of tree architecture.