CsBZR1 Family Transcription Factors in Wild and Cultural Tea Plants and Their Response to Hormone and Abiotic Stress

The BRASSINAZOLE-RESISTANT (BZR1) transcription factor family is a key transcription factor downstream of the brassinosteroid (BR) signaling pathway that plays a critical role in plant growth and resistance to environmental stress. Tea plant (Camellia sinensis) is a perennial plant with important economic value. In this study, a total of 5, 6, 7, 8, and 7 CsBZR1s were identified from the genomes of wild tea plant ('DASZ') and four tea cultivars ('Longjing 43,' 'Shuchazao,' 'Tieguanyin,' and 'Huangdan'), respectively. The phylogenetic tree analysis classified the 33 CsBZR1s into four groups, with members in the same classification having similar conserved motifs. Covariance and gene structure analysis revealed that two CsBZR1 genes (DACsBZR1.1, DACsBZR1.4) have high sequence alignment rates among the five tea genomes. One unique CsBZR1 gene present in each of 'DASZ,' 'Longjing 43,' 'Shuchazao,' and 'Huangdan.' In comparison, 'Tieguanyin' has three specific CsBZR1 genes. The upstream promoter sequences of 33 CsBZR1 genes contain many regulatory elements associated with hormone and stress responses. The expression levels of lj43CsBZR1s and sczCsBZR1s in different tissues of tea plants were significantly different. Under hormonal (GA, ABA, and BR) and abiotic stress (cold, heat, drought, and salt) treatments, most lj43CsBZR1s and sczCsBZR1s showed up-regulation in their expression levels. The relative expression levels of lj43CsBZR1s and sczCsBZR1s under GA and heat treatments were significantly higher than those under other treatments. This study provided a potential theoretical basis for the analysis of the function of CsBZR1 protein and its regulatory mechanism in response to hormone and abiotic stress in tea plants.