Expression Analysis of Brassinolide-Metabolism-Related Genes at Different Growth Stages of Pak Choi

Pak choi needs to be exposed to low temperature (vernalized) before flowering will initiate. Early bolting caused by low temperature often occurs in spring and leads to significant economic losses. Therefore, it is of great practical significance to study the flowering process of pak choi. Brassinolide (BR) plays a certain role in the flowering process of pak choi. In order to better understand the role of BR in the flowering process of pak choi, the BR content in the shoot apices of pak choi at different growth stages was determined by enzyme-linked immunosorbent assay (ELISA). The results showed that the BR content increased after low-temperature treatment. With the progress of vegetative growth, the BR content decreased and reached the lowest at 10 days after transplanting (V10), then the content increased and reached a small peak at the critical period of floral bud differentiation (S0). After initiation of floral bud differentiation, the content decreased at floral bud differentiation stage 1 (S1), and then gradually increased and reached a peak at floral bud differentiation stage 3 (S3). In order to clarify the molecular mechanism of BR content changes, we analyzed the expressions of key enzymes coding genes in the BR metabolic pathway, and found that six major synthase-encoding genes (Bra008760, Bra030023, Bra036097, Bra027405, Bra011678, and Bra025409) were upregulated at the critical period of floral bud differentiation, leading to the increase in BR content, which were consistent with changes in the BR content. By analyzing the functions of differentially expressed genes (DEGs) between the vegetative growth stage (V10) and the critical period of floral bud differentiation (S0), 21 DEGs were found to be related to BR metabolism. These findings can provide a reference for elucidating the molecular mechanism of BR regulating the flowering process of pak choi.