Spraying methyl jasmonate before harvesting can significantly increase the content of icariin in an important leaf medicinal herb, Epimedium sagittatum, by activating the expression of genes involved in flavonoid synthesis pathways

Abstract

Background: Increased icariin content during the harvesting period is one of the factors limiting the quality improvement of Epimedium sagittatum, and there is currently a lack of scientific and effective biotechnological measures.

Results: In this study, we carried out experiments involving spraying different concentrations (0 µmol·L^{- 1} as control group, 500 µmol·L^{- 1}, 1000 µmol·L^{- 1} and 1500 µmol·L^{- 1}) of methyl jasmonate (MeJA) solution on E. sagittatum leaves. To explore an effective measure to increase flavonoid content (icariin A, B, C, and II) at harvest time during cultivation and production. High concentrations of MeJA solution (1500 µmol·L^{- 1}) have a stronger stimulating effect on flavonoids in E. sagittatum leaves, especially after 24 h of treatment, the total flavonoid content increased by 44.18%, and the icariin content reached 14.36 mg·g^{- 1}, which increased by 39.6%. Principal component analysis also showed that high-concentration MeJA treatment effectively increased total flavonoid content, with the best effect observed after 24 h of high-concentration MeJA treatment. Transcriptome analysis revealed 41,468 unigenes, of which 6,920 (16.69%) showed significant differences, including 4,168 unigenes whose expressions were significantly upregulated (10.05%) and 2,752 with significantly downregulated (6.64%) expressions. We enriched the 17 most important KEGG pathways and found that they were more active following the MeJA treatment. Further analysis revealed that MeJA treatment upregulated the expression of flavonoid biosynthesis pathway genes, particularly PAL2, 4CL1, 4CL2, CHS2, CHI2, F3H, and FLS1. In addition, 37 differentially expressed transcription factors were found to be involved in the hypothetical regulatory network of the flavonoid synthesis pathway under the MeJA treatment.

Conclusions: We recommend spraying a solution of MeJA at a concentration of 1500 µmol·L^{- 1} before harvesting E. sagittatum leaves, and harvesting after 24 h can achieve a rapid increase in the content of active components in a short period of time. This study confirmed the effectiveness of MeJA treatment in enhancing the icariin content and herb quality of E. sagittatum and provided a feasible biotechnological solution for enhancing the quality of E. sagittatum during the harvesting period.

Keywords: Epimedium sagittatum; Flavonoid synthesis; Icariin; Methyl jasmonate; Reasonable harvesting.