Zinc-finger proteins are important transcription factors in plants, responding to adversity and regulating the growth and development of plants. However, the roles of the BBX gene family of zinc-finger proteins in wintersweet (Chimonanthus praecox) have yet to be elucidated. In this study, a group IV subfamily BBX gene, CpBBX19, was identified and isolated from wintersweet. Quantitative real-time PCR (qRT-PCR) analyses revealed that CpBBX19 was expressed in all tissues and that expression was highest in cotyledons and inner petals. CpBBX19 was also expressed in all flower development stages, with the highest expression detected in early initiating bloom, followed by late initiating bloom and bloom. In addition, the expression of CpBBX19 was induced by different abiotic stress (cold, heat, NaCl, and drought) and hormone (ABA and MeJA) treatments. Heterologous expression of CpBBX19 in Arabidopsis thaliana (Arabidopsis) enhanced the tolerance of this plant to salt and drought stress as electrolyte leakage and malondialdehyde (MDA) concentrations in transgenic Arabidopsis after stress treatments were significantly lower than those in wild-type (WT) plants. In conclusion, this research demonstrated that CpBBX19 plays a role in the abiotic stress tolerance of wintersweet. These findings lay a foundation for future studies on the BBX gene family of wintersweet and enrich understanding of the molecular mechanism of stress resistance in wintersweet.

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.