Genome-wide identification of BcMYB in Bupleurum Chinense DC. and its regulatory roles in saikosaponins synthesis under temperature stress.

BACKGROUND: MYB transcription factors play critical roles in secondary metabolite biosynthesis in medicinal plants and are crucial for abiotic stress responses. However, no studies have identified BcMYB genes in Bupleurum chinense DC. or analyzed their expression profiling under temperature stress. The role of BcMYB in ​B. chinense's response to temperature stress and its regulation of saikosaponins synthesis remains unclear.

RESULTS: This study performed a genome-wide identification of the BcMYB gene family in B. chinense using its genomic data, and analyzed the changes in saikosaponins content, physiological indicators, and BcMYB expression patterns under temperature stress, along with their correlations with saikosaponin biosynthesis. A total of 85 BcMYBs genes were identified, classified into four subfamilies, with amino acid lengths ranging from 306 to 482 aa and relative molecular masses between 23,710.84 and 53,062.36. Except for BcMYB10 and BcMYB50, all other BcMYB genes were localized in the nucleus. Most BcMYB promoter regions contained low-temperature and drought-responsive elements. BcMYB genes underwent strong purifying selection after duplication. Short-term temperature stress (6 days) significantly stimulated saikosaponins synthesis: Ss-a content increased by 94% under low temperature (15 °C) and 34% under high temperature (35 °C), accompanied by elevated antioxidant enzyme activities (SOD: 58%, POD: 41%) and MDA accumulation. Temperature stress predominantly upregulated upstream genes in the saikosaponins biosynthesis pathway (1-Deoxy-D-xylulose-5-phosphate synthase (DXS), 1-Deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), Isopentenyl pyrophosphate isomerase (IDI), 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR)), while mid- and downstream genes (Farnesyl pyrophosphate synthase (FPS), β-Amyrin synthase (β-AS), Cytochrome P450 monooxygenase (P450-1 P450-8)) were more responsive to high temperature. BcMYB28, 41, 44, 46, 47, 68, and 79 were significantly upregulated under both low and high temperatures (p < 0.05), whereas BcMYB25 and 56 were specifically induced by low temperature. BcMYB25, 28, 41, 44, 46, 47, 56, 68, and 79 demonstrated strong connectivity and correlations with saikosaponins biosynthesis genes and saikosaponins content.

CONCLUSIONS: The physiological responses of B. chinense to temperature stress and its secondary metabolic regulatory network exhibit dynamic synergistic characteristics. BcMYB, a critical transcription factor in B. chinense, plays a pivotal role in adapting to temperature fluctuations under temperature stress. This transcription factor may participate in establishing a "temperature signal-regulatory gene-metabolite" cascade regulatory network, thereby modulating the synthesis of saikosaponins in B. chinense. In agricultural practices, harvesting B. chinense after gradual cooling and exposure to low-temperature conditions for 6-12 days significantly enhances medicinal material quality.