Chrysanthemums are among the world’s most popular cut flowers, with their color being a key ornamental feature. The formation of these colors can be influenced by high temperatures. However, the regulatory mechanisms that control the fading of chrysanthemum flower color under high-temperature stress remain unclear. This study investigates the impact of high temperatures on the color and biochemical responses of purple chrysanthemums. Four purple chrysanthemum varieties were exposed to both normal and elevated temperature conditions. High-temperature stress elicited distinct responses among the purple chrysanthemum varieties. ‘Zi Feng Che’ and ‘Chrystal Regal’ maintained color stability, whereas ‘Zi Hong Tuo Gui’ and ‘Zi lian’ exhibited significant color fading, particularly during early bloom stages. This fading was associated with decreased enzymatic activities, specifically of chalcone isomerase (CHI), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS), indicating a critical period of color development under heat stress. Additionally, the color fading of ‘Zi Lian’ was closely related to the increased activity of the peroxidase (POD) and polyphenol oxidase (PPO). Conversely, a reduction in β-glucosidase (βG) activity may contribute significantly to the color steadfastness of ‘Zi Feng Che’. The genes Cse_sc027584.1_g010.1 (PPO) and Cse_sc031727.1_g010.1 (POD) might contribute to the degradation of anthocyanins in the petals of ‘Zi Hong Tuo Gui’ and ‘Zi Lian’ under high-temperature conditions, while simultaneously maintaining the stability of anthocyanins in ‘Zi Feng Che’ and ‘Chrystal Regal’ at the early bloom floral stage. The findings of this research provide new insights into the physiological and biochemical mechanisms by which chrysanthemum flower color responds to high-temperature stress.

The development of branching plays a pivotal role in the cultivation of ornamental chrysanthemums, as it dictates the ultimate morphology and quality of the plants. Strigolactones (SLs) are associated with apical dominance to indirectly inhibit shoot branching. Chrysanthemum morifolium ‘Baltasar’ in this study was subjected to treatment with three hormones: auxin (IAA), 6-BA, and GR24. Following the exogenous application of GR24 and IAA, a significant reduction in both the length and quantity of lateral buds on chrysanthemums was observed. Additionally, there was a notable down-regulation in the expression levels of CmPIN1 (associated with auxin transport) and CmIPT3, which is involved in cytokinin (CK) synthesis. After the application of 6-BA, there was a significant increase in both the length and quantity of lateral buds on chrysanthemums. Subsequently, the separate application of IAA and 6-BA to C. morifolium ‘Baltasar’ notably induced the expression of CmMAX1, a gene involved in the biosynthesis of strigolactones, and CmSMXL6, a gene associated with the signaling pathway of SLs, suggesting a negative regulatory role for SLs and auxin in chrysanthemum lateral buds, while CK demonstrated positive regulation. Cloning and expression analysis of CmSMXL6, a member of the D53/SMXL gene family in chrysanthemum, revealed its up-regulation following GR24 treatment, peaking at 9 h. The overexpression of CmSMXL6 in Arabidopsis thaliana promoted increased numbers of primary and secondary branches. In transgenic lines, genes associated with SLs synthesis (AtMAX1, AtMAX2, and AtMAX3) exhibited varying degrees of down-regulation, while the branching-inhibitory gene AtBRC1 also displayed decreased expression levels. These findings suggest that CmSMXL6 plays a role in promoting branching.

FLOWERING LOCUS T (FT) is an important factor for integrating flowering signals through the photoperiod pathway, which significantly promotes flowering. Most chrysanthemum varieties are short-day plants, sensitive to the photoperiod, which limits their ornamental and annual production supply. In this study, we aim to analyze the nutrients and flowering-related genes of chrysanthemums with different photoperiod types and to clone and verify the function of the flowering-related gene CmFT. We found that the formation of floral buds requires the accumulation of starch while consuming soluble sugars and the expression patterns of flowering-related genes GIGANTEA (GI), CONSTANS (CO), and FT in C.morifolium ‘Zilian’ and C. morifolium ‘Zihongtuogui’ had a certain synchronization during floral buds differentiation according to our quantitative validation, and the expression levels of CmGI, CmCO and CmFT in C. morifolium ‘Zihongtuogui’ were higher than those in C. morifolium. ‘Zilian’ in the later stage of differentiation. CmFT was cloned from photosensitive chrysanthemums-C. morifolium ‘Zihongtuogui’ and polypeptide alignment and phylogenetic analysis showed that CmFT was clustered in FT-like subfamily. In further functional verification, we obtained two Arabidopsis transgenic lines. Our results showed that CmFT transgenic ft mutant lines can significantly accelerate flowering in Arabidopsis. Thus, we can initially confirm that CmFT plays an important role in promoting flowering, which may be the key reason for the photosensitivity of C. morifolium ‘Zihongtuogui’. Overall, the results of this study are of great importance in revealing the flowering mechanism of different photoperiod types of chrysanthemums.

The basic Helix-Loop-Helix (bHLH) transcription factor family is crucial for plant growth, development, and stress response regulation. Despite previous studies on the bHLH gene family in Lagerstroemia indica, many bHLH genes remain unidentified, hindering further research on LibHLHs. Here, we identified 150 LibHLHs from the genome of L. indica and categorized them into 12 subfamilies (comprising 25 subgroups) showing conservation within subgroups. Cis-acting element analysis suggests roles in plant development, and responses to light, hormones, and stress. Examination of gene expression patterns highlighted the potential involvement of specific genes, such as LibHLH25 in subgroup IIIf, LibHLH68, LibHLH106, and LibHLH142 in subgroup IIIb, and LibHLH112 in subgroup VIIa, in anthocyanin biosynthesis in leaves of L. indica. This investigation enhances our comprehension of the complexity of the bHLH gene family and highlights the potential roles of LibHLHs in anthocyanin biosynthesis in L. indica, offering valuable insights for future genetic breeding endeavors.