Background/Objectives: The 3-ketoacyl-CoA synthase (KCS) enzyme is a key and rate-limiting component in the biosynthesis of very long-chain fatty acids (VLCFAs). Through controlling VLCFA production, KCS plays an essential role in plant cuticle formation. The necrotrophic fungus Botrytis cinerea can infect all aboveground parts of rose plants (flowers, leaves, and stems), causing severe economic losses. KCS restricts pathogen invasion by influencing cuticle formation and enhances tolerance to environmental stresses. While the KCS gene family has been well-studied in some plants, it remains unexplored in rose (Rosa × hybrida Hort.), a species of significant ornamental and economic value. Methods: In this study, we conducted a genome-wide analysis of the RcKCS gene family in rose, identifying 18 non-redundant genes. Phylogenetic, structural, and synteny analyses were performed to investigate the evolutionary relationships, gene architecture, and duplication events. The expression patterns of RcKCS genes in rose petals during B. cinerea infection were examined, and transient overexpression and silencing of RcKCS6 were used to study its function. Results: RcKCS6 was found to be upregulated during gray mold infection, and transient overexpression reduced lesion size on infected petals. Conclusions: Our study provides the first comprehensive analysis of the RcKCS gene family in rose and highlights RcKCS6 as a potential candidate for improving resistance to gray mold in rose through molecular breeding.

Strigolactones (SLs), as a class of novel plant hormones, play important roles in the regulation of plant branching. However, their function in branch development of wintersweet remains unclear. In this study, a gene involved in SLs biosynthesis, CpD27, was identified and isolated from wintersweet. The sequence characteristics, expression patterns, subcellular localization, and functional analysis through heterologous expression in Arabidopsis thaliana were investigated. Multiple sequence alignment showed that CpD27 contains the conserved D27 protein domain DUF4033. Quantitative real-time PCR analysis revealed that CpD27 is expressed in various vegetative organs of wintersweet, with the highest expression in leaves, followed by axillary buds. It is also expressed in all floral organs, with the highest expression level in the outer petals. CpD27 expression is induced by hormones (ABA and ACC) and low temperature (4 °C). Subcellular localization analysis indicated that CpD27 is localized in the chloroplasts of Arabidopsis. Heterologous expression of CpD27 in Arabidopsis delayed bolting. The number of both rosette branches and cauline branches in transgenic plants was reduced compared with wild-type plants. In addition, the expression of AtBRC1 was significantly upregulated in transgenic lines, suggesting that CpD27 has a function similar to that of its homolog in Arabidopsis. Overall, these results indicate that CpD27 plays a conserved role in the SLs-mediated branching pathway, which regulates branch development in wintersweet. This study provides a molecular and theoretical basis for further understanding branch development in wintersweet.