Hydrangea macrophylla, renowned for its large inflorescences and a diverse range of colors, highlights a significant limitation in current gene function research, which is the lack of effective molecular genetic tools. This study utilized a tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) system to investigate gene function through posttranscriptional gene silencing in H. macrophylla for the first time. The ortholog of phytoene desaturase (PDS) in H. macrophylla, termed HmPDS, was identified. Infection of tissue-cultured seedlings with TRV-HmPDS led to photobleaching of the leaves. Additionally, infection with TRV containing the HmCHS1 fragment in the flowers resulted in decreased anthocyanin production in sepals and a lightening of sepal coloration in the infected flowers. The phenomena and RT-qPCR results proved that the PDS and CHS genes of hydrangea were successfully silenced via the vacuum infiltration method. Furthermore, the introduction of TRV-HmF3′5′H revealed a decrease in delphinidin-3-glucoside content in sepals and caused a color change in the sepals from blue to pink. This study demonstrated that the TRV-VIGS system was successfully established in H. macrophylla and effectively applied to the function analysis of HmF3′5′H.

Hydrangea macrophylla (H. macrophylla), a species in the genus Hydrangea in the family Hydrangeaceae, is widely valued for its ornamental qualities in both domestic and international markets. Notably, H. macrophylla is known for its ability to accumulate aluminum (Al). Moreover, aluminum ions (Al³⁺) participate in sepal bluing. However, the underlying mechanisms of Al accumulation in the sepals remain unclear. In this study, we utilized transcriptome data from two cultivars to identify genes associated with Al accumulation. In total, 154 differentially expressed isoforms between the CK and Tr groups in the sepals of both cultivars were screened. Through gene enrichment analysis and similarity identification in the CDS (coding sequence) region, 43 differentially expressed genes were identified, including 30 upregulated and 13 downregulated genes, in the sepals of the Al treatment group. Further analysis revealed that seven of these upregulated genes are related to Al accumulation in sepals. Among the seven, the gene HmALS3.1 was identified as a potential key player in Al transport within the sepals of H. macrophylla. This study lays the groundwork for further exploration into the mechanisms by which HmALS3.1 regulates Al accumulation in H. macrophylla.

The floricultural value of Hydrangea macrophylla is significantly influenced by its distinctive blue flower coloration, which results from aluminum uptake and vacuolar complexation. However, commercial cultivation faces challenges in achieving consistent bluing while avoiding Al toxicity. This study investigated the effects of Al concentration (0–971.62 mg/L) and application period on six blue-modifiable cultivars. Optimal results were achieved with an Al₂(SO₄)₃·18H₂O concentration of 6 g/L applied from two weeks after pinching until bloom. This regimen successfully induced vibrant sepal bluing without impairing chlorophyll content or plant growth. Furthermore, it enhanced tissue concentration of essential nutrients, including N, K, Mg, Fe, Zn, Mn, Cu, B, and Co. This study proposes a robust technical and theoretical framework for optimizing Al application to ensure consistent sepal color, which provides technical support for commercial production.

Light intensity strongly influences the morphological development and photoprotective responses of in vitro plantlets, yet the optimal conditions for hydrangea remain undefined. This study investigated the effects of five light intensity gradients (TrA: 80–120 lux, TrB: 380–480 lux, TrC: 1500–1800 lux, TrD: 3800–4000 lux, TrE: 6000–6400 lux) on Hydrangea macrophylla ‘Qingtian’ plantlets. Plantlets exhibited optimal growth at TrB, showing maximal biomass, leaf expansion, chlorophyll content, and root activity, accompanied by low antioxidant enzyme activities and soluble sugar levels. Nutrient accumulation was greater under low light than under high light conditions. Transcriptome analysis of treatments (TrB and TrE) with marked phenotypic differences revealed 7119 differentially expressed genes (DEGs). Of these, 4582 genes were up-regulated and 2537 were down-regulated. The up-regulated genes were significantly enriched in pathways related to cell walls, the microtubule cytoskeleton, and developmental processes, which are involved in the plant growth and development process, such as photosynthesis, nutrient ion transport and regulation, as well as plant hormone responses and transport; whereas the down-regulated genes were significantly enriched in pathways related to carbohydrate metabolism, oxidoreductase activity, and glutathione metabolism, suggesting that high light stress impairs growth by disrupting carbon and antioxidant processes. These results demonstrated that 380–480 lux is the optimal light intensity for ‘Qingtian’ Hydrangea macrophylla in vitro plantlets. This study provides a foundation for optimizing culture conditions and offers new insights into the molecular regulation of light-responsive genes.

The xyloglucan endotransglucosylase/hydrolase (XTH) gene family plays key roles in plant cell wall remodeling and aluminum (Al) stress responses. However, a systematic genome-wide identification and functional characterization of the XTH gene family in Hydrangea macrophylla has not yet been reported. In this study, a total of 29 HmXTH genes were identified from the H. macrophylla genome. Phylogenetic analysis classified these genes into three distinct subgroups all of which contained the conserved catalytic motif DEIDFEFLG. Gene structure analysis revealed that most HmXTH genes possessed two conserved domains Glyco_hydro_16 and XET_C. Promoter analysis identified an enrichment of cis-acting elements associated with stress responses, hormone signaling, growth and development binding sites, while expression profiling demonstrated tissue-enriched patterns. Under Al stress, HmXTH6 was the only gene significantly upregulated across all three tissues (roots, stems, and leaves), suggesting its potential involvement in Al accumulation. Virus-induced gene silencing revealed that silencing HmXTH6 significantly decreased Al content by 86.8% and weakened Al signals in cell wall of leaves compared to controls, confirming its pivotal role in Al sequestration. These findings lay a theoretical foundation for elucidating the molecular mechanisms underlying Al hyperaccumulation.