Objective  SPL (SQUAMOSA promoter binding protein-like) is a plant-specific transcription factor and plays crucial roles in the growth and development of plants. It participates in multiple processes such as plant phase transformation, flower development, sporogenesis, leaf and root development, and stress response. Exploring the cis-acting elements of the promoter region of the BpSPL6 gene, as well as the expression pattern under normal and stress conditions, this paper provides a reference for further study of the function of BpSPL6 gene and also provides a basis for understanding the stress resistance mechanism of Betula platyphylla.

  Method  Using the total DNA of tissue-cultures B. platyphylla in this laboratory as a template, the 1 703 bp promoter sequence of BpSPL6 gene was cloned by PCR. The cis-elements of the promoter region were analyzed using PLACE and Plant CARE web tools. We constructed the BpSPL6 gene promoter-driven GUS expression vector, which was transformed into Arabidopsis thaliana. Transgenic A. thaliana was subjected to stress experiments, and GUS staining was used to analyze the expression pattern of the BpSPL6 gene promoter.

  Result  A 1 703 bp promoter sequence of BpSPL6 gene was cloned from B. platyphylla genomic DNA. Sequence analysis showed that the BpSPL6 gene promoter included core promoter elements TATA-box and CAAT-box, as well as cis-elements for specific parts (root and pollen), hormone response elements (auxin, gibberellin, salicylic acid, abscisic acid) and dehydration response elements. The GUS staining results of transgenic A. thaliana showed that the expression of GUS gene driven by BpSPL6 gene promoter had spatiotemporal specificity. Throughout the development of A. thaliana, the GUS gene driven by BpSPL6 gene promoter was expressed in euphylla, but the expression sites were different. As the leaf grew, it was first expressed at the tip of the leaf, then expanded to the leaf vein and reached the entire leaf, and the expression level gradually increased. At the same time, the GUS gene driven by BpSPL6 gene promoter was also expressed in the roots during vegetative growth. When transgenic A. thaliana was subjected to sodium chloride and mannitol stress, the expression level of GUS gene driven by BpSPL6 gene promoter decreased compared with control. Comparing the two stresses, the expression level of GUS gene changed more after being subjected to sodium chloride stress, indicating that the response to sodium chloride stress was stronger.

  Conclusion  BpSPL6 gene may be involved in plant leaf and root development and response to salt and drought stress.