Genome-wide identification of SWEET gene family and functional analysis of BcSWEET1-2 associated with flowering in flowering Chinese cabbage (Brassica campestris).

Abstract

Background: The bolting and flowering processes are crucial for the yield of stem vegetables and require sugar support. Sugar is synthesized through photosynthesis in the leaves and transported to the stems via transmembrane transport. Brassica campestris (flowering Chinese cabbage) is a unique vegetable that does not require vernalization for flowering and has a distinct flowering regulation mechanism. "Sugars Will Eventually be Exported Transporters" (SWEET), a relatively newly identified group of sugar transporters, play vital roles in plant development. However, the role of B. campestris SWEET (BcSWEET) genes in the growth and development of flowering Chinese cabbage remains to be elucidated.

Results: In this study, 32 BcSWEET genes were identified, which are unevenly distributed across nine chromosomes and classified into four groups based on their homology with Arabidopsis. Significant differences were observed in the physicochemical properties, motif composition, and gene structure of the BcSWEET gene family. However, all BcSWEET proteins are predicted to be localized in the cell membrane. Prediction of transmembrane regions showed that all members contained the MtN3/saliva domain. The BcSWEET promoter regions contain different cis-regulatory elements involved in developmental and hormonal regulation, stress responses, and light-responsive regulation. Expression pattern analysis of the 32 BcSWEET genes revealed that most are associated with reproductive growth in different tissues, with the majority being upregulated in petals and flower buds. BcSWEET1-2 has been confirmed to be localized in the cell membrane and to function as a hexose transporter. Overexpression of BcSWEET1-2 in Arabidopsis promotes stem carbohydrate accumulation, upregulates flowering gene expression, enhances Arabidopsis stem elongation, and advances flowering time.

Conclusions: This study systematically identified the BcSWEET gene family in flowering Chinese cabbage and characterized its physicochemical properties, evolutionary relationships, and expression patterns. Further analysis demonstrated that some BcSWEET gene members may play crucial roles in flowering regulation. These findings provide theoretical guidance for further research on the role of SWEET-induced sugar accumulation in flower development in flowering Chinese cabbage.