Strigolactones (SLs) are a class of important hormones in the regulation of plant branching. In the model plant Arabidopsis, AtMAX1 encodes a cytochrome P450 protein and is a crucial gene in the strigolactone synthesis pathway. Yet, the regulatory mechanism of MAX1 in the shoot branching of wintersweet (Chimonanthus praecox) remains unclear. Here we identified and isolated three MAX1 homologous genes, namely CpMAX1a, CpMAX1b, and CpMAX1c. Quantitative real-time PCR (qRT-PCR) revealed the expression of CpMAX1a in all tissues, being highest in leaves, whereas CpMAX1b was only expressed in stems, while CpMAX1c was expressed in both roots and stem tips. However, CpMAX1a’s expression decreased significantly after decapitation; hence, we verified its gene function. CpMAX1a was located in Arabidopsis chloroplasts. Overexpressing CpMAX1a restored the phenotype of the branching mutant max1–3, and reduced the rosette branch number, but resulted in no significant phenotypic differences from the wild type. Additionally, expression of AtBRC1 was significantly upregulated in transgenic lines, indicating that the CpMAX1a gene has a function similar to the homologous gene of Arabidopsis. In conclusion, our study shows that CpMAX1a plays a conserved role in regulating the branch development of wintersweet. This work provides a molecular and theoretical basis for better understanding the branch development of wintersweet.

TCP transcription factors represent a crucial family of plant regulators that contribute significantly to growth and developmental processes. Although the TCP gene family has been extensively studied in various plant species, research on Chimonanthus praecox (wintersweet) remains limited. Here, we performed genome-wide identification and analysis of the TCP gene family in C. praecox and identified 22 CpTCP genes. We further systematically examined the associated physicochemical properties, evolutionary relationships, gene structures, and regulatory features. Analysis revealed that all CpTCP proteins possess a conserved TCP domain, and subcellular localization prediction indicated their localization in the nucleus. Promoter analysis revealed that multiple cis-elements are associated with abiotic stress responses and plant growth regulation. Further analysis revealed high CpTCP2 expression in the leaves and stamen, with significantly increased levels during flower senescence. CpTCP2 expression was upregulated in response to methyl jasmonate (MeJA), salicylic acid, abscisic acid, and shade. CpTCP2 overexpression in Arabidopsis thaliana resulted in a reduced leaf area, delayed flowering, and increased rosette leaf numbers. Moreover, MeJA treatment accelerated leaf senescence in CpTCP2 transgenic Arabidopsis. These findings provide insights into the evolutionary characteristics of the TCP family in C. praecox, highlighting the functional role of CpTCP2 in regulating leaf development and flowering time in Arabidopsis, thereby offering valuable genetic resources for wintersweet molecular breeding.

Strigolactones (SLs), as a class of novel plant hormones, play important roles in the regulation of plant branching. However, their function in branch development of wintersweet remains unclear. In this study, a gene involved in SLs biosynthesis, CpD27, was identified and isolated from wintersweet. The sequence characteristics, expression patterns, subcellular localization, and functional analysis through heterologous expression in Arabidopsis thaliana were investigated. Multiple sequence alignment showed that CpD27 contains the conserved D27 protein domain DUF4033. Quantitative real-time PCR analysis revealed that CpD27 is expressed in various vegetative organs of wintersweet, with the highest expression in leaves, followed by axillary buds. It is also expressed in all floral organs, with the highest expression level in the outer petals. CpD27 expression is induced by hormones (ABA and ACC) and low temperature (4 °C). Subcellular localization analysis indicated that CpD27 is localized in the chloroplasts of Arabidopsis. Heterologous expression of CpD27 in Arabidopsis delayed bolting. The number of both rosette branches and cauline branches in transgenic plants was reduced compared with wild-type plants. In addition, the expression of AtBRC1 was significantly upregulated in transgenic lines, suggesting that CpD27 has a function similar to that of its homolog in Arabidopsis. Overall, these results indicate that CpD27 plays a conserved role in the SLs-mediated branching pathway, which regulates branch development in wintersweet. This study provides a molecular and theoretical basis for further understanding branch development in wintersweet.