Insights into the molecular mechanism underlying cold-induced flavonoids biosynthesis in callus of a Tibetan medicinal plant Saussurea laniceps

Saussurea laniceps is renowned for its extraordinary medicinal ingredients diversity, which is an important Tibetan medicinal plant in China. Flavonoids play an important role in the medicinal efficacy of S. laniceps. The species, however, has become increasingly scarce and endangered. Therefore, the use of callus to propagate medicinal resources is of great significance. We found that cold acclimation increased flavonoids content in S. laniceps callus. RNA-seq revealed a total of 18,414 and 21,215 differentially expressed genes at 6 d and 9 d cold (4 °C) periods, respectively. Besides, 456 differential expressed transcriptional factor genes were identified, among which AP2-EREBP, WRKY, NAC, MYB, bHLH and WD40 had the ability to induce the transcription of genes associated with flavonoid synthesis. A total of 34 unigenes were identified and linked to the flavonoids and related derivative biosynthesis pathway. The high expression levels of genes in regulating flavonoids biosynthesis (e.g., PAL, 4CL, CHS, CHI and F3’H) were identified. Besides, 66 up-regulated transporter genes were also detected, including the ATP-binding cassette (ABC) family (23), GST (13), MATE (12), vacuolar-associated proteins (8) and H⁺-ATPase (10). Consequently, these findings suggest that cold-acclimated callus could be an effective alternative resource for flavonoids in S. laniceps, which is valuable for the conservation and usage of this wild and endangered plant.