(1) Background: The bHLH (basic helix-loop-helix) transcription factor family is one of the most abundant in plants and is involved in plant growth, development, and abiotic stress responses. Notably, the functions of most bHLH family members remain poorly characterized. (2) Results: CmbHLH112, a nuclear-localized bHLH transcription factor from chrysanthemum, exhibits transcriptional activation activity. Overexpression of CmbHLH112 in Arabidopsis significantly promotes flowering and enhances drought resistance. qRT-PCR analysis revealed that CmbHLH112 regulates flowering time by affecting the expression of key flowering genes, including FT, SOC1, LFY, and FLC. Under drought stress, CmbHLH112 overexpression plants showed reduced ROS accumulation compared with wild-type plants, accompanied by elevated activities of key antioxidant enzymes and increased proline content. Moreover, transgenic plants exhibited lower MDA concentrations and reduced water loss rates under drought conditions, further indicating enhanced stress resilience. Overexpression of CmbHLH112 also upregulates ABA levels under drought stress, while simultaneously promoting the expression of genes involved in ABA biosynthesis and ABA signaling pathways. (3) Conclusions: Our results demonstrate that heterologous overexpression of CmbHLH112 in Arabidopsis enhances drought tolerance and promotes flowering. Thus, CmbHLH112 is proposed to play a dual role in modulating flowering time and drought tolerance, at least partly by regulating ABA biosynthesis.

Hybrid tea roses (Rosa hybrida) are economically important horticultural crops and highly susceptible to heat stress, which significantly impacts flower quality and yield. As a key member of the heat shock protein (HSP) family, HSP70 protein acts as a molecular chaperone and exhibits diverse abiotic stress response functions in plants. A total of 113 HSP70 transcription factors (TFs) with varying physical and chemical properties were identified in the genome of hybrid tea rose. Phylogenetic analysis showed that the identified TFs could classify into three (I, II, and III) subfamilies, with most members (51 TFs) falling in subfamily II. Wide gene structural variations were observed among the three subfamilies, with group I and II members lacking introns, while group III members only harbored 1~4 exons and introns. Numerous cis-acting elements associated with abiotic stress, hormone response, growth and development responses, as well as light response were detected in the HSP70 gene promoters. In addition, protein interaction networks predicted a wide range of interactions between different hybrid tea rose HSP70 subfamilies. Gene expression analysis revealed that 57 HSP70 genes had strong organ specificity and response to heat stress in the hybrid tea rose plants. Notably, the expression levels of two RhHSP70 genes, RhHSP70-69 and RhHSP70-88, were significantly increased after heat stress, indicating that these two genes might be crucial for plant heat stress response. Subcellular localization of RhHSP70-69 and RhHSP70-88 revealed that their proteins were located in the nucleus. Our results are not only useful for future evaluation of the regulatory roles of RhHSP70 genes in the hybrid tea rose growth and development, but also provides key genes for future molecular breeding of heat tolerant plants.

Chrysanthemum is one of the world’s four main cut flowers. However, postharvest drought stress severely disrupts water homeostasis, triggering reactive oxygen species burst and membrane lipid peroxidation, thereby reducing its ornamental quality and vase life. Melatonin serves as a multifunctional antioxidant and stress regulator. This study demonstrated that 200 μmol L⁻¹ melatonin effectively alleviated drought-induced leaf wilting, maintained relative water content, decreased the accumulation of MDA, H₂O₂, and O₂^•−, and enhanced the activities of SOD, CAT, POD, and APX. Concurrently, non-enzymatic antioxidants (proline, GSH, ASA) accumulated to high levels. RNA-seq analysis revealed that drought affects pathways closely related to the production of antioxidant and osmoprotectant metabolites, while melatonin initiated extensive transcriptional reprogramming and responded to drought stress through distinct pathways at the early (12 h) and late (24 h) treatment stages. Melatonin also modulated key transcription factor families, including bHLH, NAC, ERF, MYB, and bZIP. Collectively, exogenous MT mitigates drought damage in chrysanthemum cut flowers by coordinating antioxidant systems and complex transcriptional regulatory networks. This study provides a theoretical foundation for improving postharvest drought tolerance and prolonging the vase life of cut flowers.

Leaf senescence is a major factor limiting the vase life of chrysanthemum cut flowers, for which the early senescence stage is vital but remains not fully studied. Exploring its mechanism enables extending the vase life of chrysanthemum cut flowers. In this study, physiological results showed that early senescence displayed continuous chlorophyll degradation, elevated MDA and H₂O₂ contents, and gradually increased activities of SOD, POD, and CAT. Transcriptomic analysis revealed stage-specific transcriptional reprogramming: the first stage (0–6 d) was dominated by stress responses, MAPK signaling, and metabolic adaptation, whereas the second stage (6–12 d) was mainly involved in plant hormone signal transduction and senescence execution. A total of 6,194 core DEGs shared by both stages were identified, with WRKY, bHLH, NAC, and ERF as the predominant transcription factor families. The expression of circadian clock genes was significantly disrupted, while multiple senescence-associated genes were continuously upregulated. Among these differentially expressed TFs, CmHSFC1 exhibited the strongest induction. Moreover, VIGS-mediated silencing of CmHSFC1 markedly delayed leaf senescence and chlorophyll loss. These results reveal the sequential regulatory network of postharvest early leaf senescence in chrysanthemum and identify CmHSFC1 as a positive key regulator of early senescence, providing valuable gene resources for the genetic improvement of cut-flower vase life.