[Cloning and expression analysis of 8 bHLH transcription factors in Panax quinquefolius]

A total of 8 bHLH transcription factors were cloned from Panax quinquefolius and the response of them to methyl jasmonate(MeJA) was studied.To be specific, based on the preliminary transcriptome screening, 8 bHLH transcription factors were cloned with seedlings which had been cultured for 3 weeks.The content of ginsenosides Rg_1, Re, and Rb_1, and total saponins in the adventitious roots of P.quinquefolius was determined at different time of MeJA treatment by high performance liquid chromatography(HPLC) and spectrophotometry.Real-time quantitative polymerase chain reaction(PCR) was used to detect the relative expression of 8 transcription factors after MeJA treatment.The correlation between the relative expression of the 8 transcription factors and the saponin content after MeJA treatment was checked by Pearson's correlation analysis.The results showed that the PCR products(Pq-bHLH21-Pq-bHLH28) of the 8 bHLH transcription factors were 762-2 013 bp in length.They were submitted to NCBI to obtain the Genbank access numbers.The proteins yielded from Pq-bHLH21-Pq-bHLH28 showed amino acid sequence identity of 24.90%, and each amino acid sequence had the bHLH(Basic Helix-loop-helix) conserved domain and belonged to the bHLH family.The 5 amino acid sequences of Pq-bHLH22 and Pq-bHLH24-Pq-bHLH27 contained the bHLH-MYC N domain, which belonged to the MYC transcription factors.Pq-bHLH21-Pq-bHLH28 responded to MeJA within 48 h of treatment.At 72 h, the expression of Pq-bHLH24 reached 106.53 folds the highest in the treatment group.Pq-bHLH25, Pq-bHLH27, and Pq-bHLH28 showed synergic expression.Pq-bHLH21 may re-gulate the biosynthetic pathway of ginsenoside Rb_1, while Pq-bHLH22, Pq-bHLH25, and Pq-bHLH28 were in significantly positive correlation with the biosynthetic pathway of ginsenoside Re.The result lays a foundation for further verifying the regulation of ginsenoside biosynthesis by bHLH transcription factors.