Lateral branching contributes to plant architecture and agricultural yield. In apple (Malus domestica), the dormancy of axillary buds constrains early branching and fruit production. Among various phytohormones, strigolactones (SLs) play a pivotal role regulating axillary bud outgrowth. This study investigates the inhibitory effects of SLs on apple axillary bud growth and elucidates the underlying molecular mechanisms. Treatment with the SL analog racemic-GR24 (rac-GR24) markedly inhibited the outgrowth of axillary buds. We discovered that the transcription factor in apple SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 6 (MdSPL6) interacts with SUPPRESSOR OF MAX2-LIKE 7 (MdSMXL7), a key component of SL signaling, to regulate branching patterns. The Mdspl6 mutant exhibited enhanced lateral branching, confirming the role of MdSPL6 as a suppressor of bud growth. Through DNA affinity purification sequencing (DAP-seq), we identified apple HOMEOBOX PROTEIN53 (MdHB53) and TEOSINTE BRANCHED1, CYCLOIDEA, PCF18 (MdTCP18) as downstream target genes of MdSPL6. Overexpression of these genes led to elevated levels of abscisic acid (ABA), implicating the function of ABA in the SL-mediated inhibition of bud outgrowth. Our results demonstrate that SLs regulate apple axillary bud growth through MdSPL6 and its downstream targets by modulating ABA levels, offering insights into the genetic control of plant architecture and identifying potential targets for breeding apple varieties with optimized branching and enhanced yield.

Blossom-end rot (BER) in tomatoes is a physiological disorder primarily caused by the disruption of calcium absorption and transport. This study cultivated tomatoes using a trough-based vermiculite system. Two treatments were established: a calcium-deficient nutrient solution and a calcium-deficient nutrient solution supplemented with 0.1 mg/L BR (n = 40 plants per treatment). The activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), as well as the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), were measured in the leaves. Calcium ion content was also determined in various plant parts. Statistical analysis of differences was performed using Duncan’s multiple range test at a significance level of p < 0.01. Concurrently, transcriptome sequencing of root, stem, and leaf tissues was conducted via high-throughput sequencing technology. The results showed that foliar application of BR under calcium deficiency significantly reduced the incidence of BER (from 26.67% to 6.67%) and effectively increased calcium ion content in leaves, stems, and roots. At the physiological level, BR treatment markedly enhanced the activities of CAT, POD, and SOD in leaves (by 105.70%, 117.12%, and 82.77%, respectively), while reducing H₂O₂ and MDA contents (by 36.90% and 16.38%, respectively). This indicates that BR alleviates membrane lipid peroxidation damage by enhancing the antioxidant defense system. Gene Ontology (GO) enrichment analysis revealed that the differentially expressed genes (DEGs) were primarily involved in biological processes, such as secondary metabolic processes, response to oxygen-containing compounds, and cell wall organization. KEGG pathway analysis further indicated significant enrichment in pathways, including phenylpropanoid biosynthesis, plant hormone signal transduction, and plant–pathogen interaction. Additionally, key genes, such as the cytochrome c oxidase (COX) gene (Solyc03g013460.1), exhibited a gradient up-regulation pattern (root > stem > leaf) in the oxidative phosphorylation pathway. In conclusion, BR likely enhances tomato tolerance to calcium deficiency stress and effectively reduces BER incidence through multiple pathways: regulating calcium absorption and distribution, activating the antioxidant system, modulating hormone signaling pathways, and enhancing energy metabolism. These findings provide a theoretical basis for the application of BR in agricultural production.

Blossom-end rot (BER) in tomatoes is a physiological disorder primarily caused by disrupted calcium absorption and transport. This study aims to investigate the physiological and molecular mechanisms by which exogenous brassinolide (BR) reduces the incidence of tomato BER under calcium-deficient conditions. The results showed that under calcium deficiency, foliar spraying of BR significantly reduced the BER incidence (from 26.67% to 6.67%) and effectively increased calcium ion content in the leaves, stems, roots, and other parts of the plant. At the physiological level, BR treatment significantly enhanced the activities of CAT, POD, and SOD in the leaves (by 105.70%, 117.12%, and 82.77%, respectively), while reducing the contents of H₂O₂ (by 36.90%) and MDA (by 16.38%). This indicates that BR alleviates membrane lipid peroxidation damage by enhancing the antioxidant defense system. Transcriptome analysis further revealed that BR treatment identified 4807, 2807, and 2554 differentially expressed genes (DEGs) in the leaves, stems, and roots, respectively, with the most significant response observed in the leaves. GO functional enrichment analysis showed that these genes are mainly involved in biological processes such as secondary metabolic processes, response to oxygen-containing compounds, and cell wall organization. KEGG pathway analysis further indicated significant enrichment in pathways such as phenylpropanoid biosynthesis, plant hormone signal transduction, and plant-pathogen interaction. Additionally, several key genes, such as the cytochrome C oxidase gene (Solyc03g013460.1), exhibited a gradient up-regulation pattern of "root > stem > leaf" in the oxidative phosphorylation pathway, while photosynthesis-related genes (e.g., PsbA, PsaA, and ND family genes) were also generally up-regulated. In summary, BR likely enhances tomato tolerance to calcium deficiency stress and effectively reduces the occurrence of BER through multiple pathways, including regulating calcium absorption and distribution, activating the antioxidant system, modulating hormone signaling pathways, and enhancing energy metabolism. This provides a theoretical basis for the application of BR in agricultural production.