Abstract

Weeping forsythia ( Forsythia suspensa ) is an important medicinal and ornamental plant. However, its tissue culture propagation is hindered by genotype-dependent performance variations. In this study, we examined the physiological and molecular basis for the inferior growth of two genotypes of F. suspensa with long style (FLS), FLS-1 and FLS-2, under tissue culture conditions. Compared to FLS-2, FLS-1 exhibited significant chlorosis, reduced chlorophyll, and underdeveloped chloroplasts with disorganized thylakoids. Transcriptomic analysis revealed distinct differential gene expression in FLS-1 relative to FLS-2, including 46 photosynthesis-related DEGs. Additionally, metabolomic profiling identified 563 DEMs, with significant enrichment in 15 key KEGG pathways. Crucially, abscisic acid (ABA) biosynthesis was impaired, with downregulation of NCED genes and reduced precursor abundance, while its signaling pathway showed alterations, including an upregulated pyrabactin resistance 1-like ( PYL ) receptor and dynamically expressed protein phosphatase 2 C ( PP2C ) genes. These findings suggested that a possible genetic predisposition in FLS-1 may interfere with chloroplast development and ABA homeostasis, which together could explain its compromised growth and physiology in vitro.