Platycodon grandiflorus (Jacq.) A. DC, known for its saponin content, can potentially prevent and treat cerebrovascular diseases and COVID-19. Triterpenoid saponin biosynthesis in plants is enhanced by methyl jasmonate (MeJA) application. However, the underlying molecular mechanisms of MeJA-induced saponin biosynthesis remain unknown in P. grandiflorus. In the current study, exogenous application of 100 μmol/l MeJA was identified to be optimal for promoting saponin accumulation. RNA sequencing analysis demonstrated the PgbHLH28 gene as a key regulatory factor responding to MeJA during saponin accumulation. Overexpression of PgbHLH28 in P. grandiflorus increased saponin content, while silencing of PgbHLH28 significantly inhibited saponin synthesis, suggesting that PgbHLH28 acts as a positive regulator of saponin biosynthesis. Yeast one-hybrid and dual luciferase assays demonstrated that PgbHLH28 directly bound to the promoters of PgHMGR2 and PgDXS2 to activate gene expression. PgHMGR2 and PgDXS2 transformation promoted saponin accumulation, while silencing of these genes inhibited saponin biosynthesis. This study determined that MeJA promoted saponin accumulation in P. grandiflorus by inducing PgbHLH28 gene expression and activating downstream genes (PgHMGR2 and PgDXS2) involved in saponin biosynthesis. In conclusion, a complex regulatory network governing saponin biosynthesis following MeJA treatment was elucidated, offering a theoretical foundation for enhancing saponin content and biosynthesis efficacy in P. grandiflorus.

Trehalose, trehalose-6-phosphate synthase (TPS),and trehalose-6-phosphatase (TPP) have been reported to play important roles in plant abiotic stress and growth development. However, their functions in the flowering process of Rosa hybrida have not been characterized. In this study we found that, under a short photoperiod or weak light intensity, the content of trehalose in the shoot apical meristem of Rosa hybrida cv ‘Carola’ significantly decreased, leading to delayed flowering time. A total of nine RhTPSs and seven RhTPPs genes were identified in the genome. Cis-element analysis suggested that RhTPS and RhTPP genes were involved in plant hormones and environmental stress responses. Transcriptome data analysis reveals significant differences in the expression levels of RhTPSs and RhTPPs family genes in different tissues and indicates that RhTPPF and RhTPPJ are potential key genes involved in rose flower bud development under different light environments. The results of quantitative real-time reverse transcription (qRT-PCR) further indicate that under short photoperiod and weak light intensity all RhTPP members were significantly down-regulated. Additionally, RhTPS1a, RhTPS10, and RhTPS11 were up-regulated under a short photoperiod and showed a negative correlation with flowering time and trehalose content decrease. Under weak light intensity, RhTPS11 was up-regulated and negatively regulated flowering, while RhTPS5, RhTPS6, RhTPS7b, RhTPS9, and RhTPS10 were down-regulated and positively regulated flowering. This work lays the foundation for revealing the functions of RhTPS and RhTPP gene families in the regulation of rose trehalose.

Sugar Will Eventually be Exported Transporter (SWEET) proteins are a recently discovered group of efflux transporters that play essential roles in sugar efflux, phloem loading, reproductive tissue development and stress responses. To date, there have been no reports on the Rosa rugosa (R. rugosa) SWEET genes. In this study, we conducted a comprehensive genomic analysis of the SWEET genes, including chromosome localization, phylogenetic comparison, cis-regulatory element analysis, expression pattern analysis in different tissues, expression pattern analysis under cold stress and subcellular localization analysis. A total of 33RrSWEET members were identified and classified into four distinct clades (Clade I, Clade II, Clade III and Clade IV). They were distributed across seven chromosomes and contained cis-regulatory elements associated with hormone and stress responses. The expression of RrSWEETs showed tissue specificity, with higher expression in roots, flowers or pistils compared to other tissues. Furthermore, during the entire cold stress process, the relative expression levels of RrSWEET4, 16 and 20 were significantly upregulated, especially in the roots and stems of R. rugosa. Subcellular localization analysis revealed that RrSWEET4, 16 and 20 were located on the cell membrane. In summary, the results of this study provide a theoretical basis for future research on the functions of RrSWEET genes in R. rugosa and their role in cold tolerance responses.

Adventitious root (AR) formation is critical for the successful establishment and survival of rose (Rosa hybrida) cuttings. SCARECROW-LIKE (SCL) genes are known to regulate plant growth and development; however, their functions in rose AR formation remain poorly understood. In this study, the rooting rate of rose cuttings declined, whereas AR number increased with increasing concentrations of exogenous indole-3-butyric acid (IBA) and N-1-naphthylphthalamic acid (NPA). Most of the 36 identified RhSCL genes were significantly up-regulated during AR formation. Notably, the expression level of RhSCL3 and RhSCL33 was positively associated with AR formation under low concentrations of exogenous IBA and NPA. Both genes were expressed at higher levels in roots than in other organs and encoded nuclear-localized proteins with transcriptional activation activity. Heterologous expression of RhSCL3 and RhSCL33 in tobacco increased primary root length under exogenous IBA treatment, enhanced AR number and length, and promoted dry matter accumulation, accompanied by increased starch degradation and soluble sugar production. Compared with wild-type plants (WT), transgenic plants showed reduced indole-3-acetic acid (IAA) levels, more pronounced changes in gibberellic acid (GA₃) content, and higher activities of superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO), catalase (CAT), and indole-3-acetic acid oxidase (IAAO). These findings suggest that overexpression of RhSCL3 and RhSCL33 facilitates rooting under low-auxin conditions, and RhSCL33 acting earlier during AR development, and RhSCL3 functioning mainly at later stages. This regulatory module may provide useful genetic targets for improving vegetative propagation efficiency in rose and other horticultural or crop species.