Transcriptome profiling reveals cytokinin promoted callus regeneration in Brassica juncea

Plant hormones not only play important roles in regulating plant growth and development, but they also promote cell dedifferentiation and redifferentiation, which play an important role in tissue culture. In the present study, an efficient method of promoting callus plant regeneration for the tissue culture of Brassica juncea (L.) was proposed. We discovered that the callus could be efficiently induced into redifferentiation by 6.8 × 10− 3 µmol/l thidiazuron (TDZ), a cytokinin analogue. To analyze the molecular mechanism of tissue culture, we sequenced the transcriptome of the callus under different culture conditions at two developmental stages. A total of 5362 differentially expressed genes were identified in the TDZ treatments; among them, the expression of 4676 genes was upregulated and that of 686 was downregulated. In the cytokinin signal transduction pathway, seven genes in the Arabidopsis (Arabidopsis thaliana) response regulator (ARR) family were upregulated. In addition, cytokinin affected gene expression in other plant hormone signaling pathways, such as the auxin, ethylene, and brassinosteroid pathways. Most of these genes, such as auxin/indole-3-acetic acid (Aux/IAA) genes and ethylene response factors (ERF-1, ERF-2, and ERF-6), generally showed upregulated expression, which also participated in the regulation of callus plant regeneration. This study provides novel insight into the molecular mechanism of callus plant regeneration in Brassica juncea, which could also provide reference for other plant tissue cultures. In Brassica juncea, 6.8 × 10− 3 µmol/l TDZ resulted in the highest regeneration rate of callus, and the genes involved in cytokinin and auxin signal transduction pathways participated in the redifferentiation progress.