Transcriptional responses for biosynthesis of flavor volatiles in methyl jasmonate-treated Chrysanthemum indicum var. aromaticum leaves

Abstract

Chrysanthemum indicum var. aromaticum (Ci. aromaticum) is an important aromatic plant in genus Chrysanthemum for its extraordinary flavors and unique aroma. Methyl jasmonate (MeJA) has been successfully used as an effective elicitor to improve the quality of aroma by promoting flavor volatiles in Ci. aromaticum leaves. Previous studies focused mainly on the extraction of essential oils as well as their aromatic components from gelatinous secretion of glandular hair of the Ci. aromaticum. However, there has been no study on their aroma formation at the molecular level. Therefore, the information about the transcriptome of Ci. aromaticum leaves, and specifically, the description of changes in gene expression in response to MeJA, is needed for a better understanding of the biological mechanisms of the MeJA-mediated biosynthesis of volatiles in Ci. aromaticum. Transcriptome sequencing was performed on leaves of Ci. aromaticum under different induction treatments of MeJA. A total of 176,091 unigenes were obtained, and 69.94 % of them could be annotated in at least one database. In the comparison groups of 0.25 % MeJA-treated for 4 h vs control (MJ4vsCtrl), 0.25 % MeJA-treated for 24 h vs control (MJ24vsCtrl), and 0.25 % MeJA-treated for 24 h vs 0.25 % MeJA-treated for 4 h (MJ24vsMJ4), 750, 650, and 313 DEGs were obtained, respectively. These DEGs were enriched in 33 secondary metabolic pathways. After analyses of the expression heatmaps of DEGs involved in jasmonic acid biosynthetic and signal transduction pathway, terpenoid biosynthetic pathway, phenylpropanoid metabolism pathway, fatty acid metabolism pathway, as well as differentially expressed post-plant modification enzymes, and transcription factors related to secondary metabolism, we found that most of the DEGs were up-regulated by the MeJA. The results of qRT-PCR were basically consistent with those of transcriptome sequencing, indicating that the gene expression profile data of transcriptome sequencing were reliable. This is the first de novo transcriptome sequencing reported in Ci. aromaticum. The transcriptome analysis showed that exogenous application of MeJA could induce expression of genes in signal transduction and secondary metabolism, especially for the biosynthetic pathways of flavor volatiles. The present results have provided some insights of the mechanisms how MeJA activates the biosynthetic pathways of volatile metabolites in the Ci. aromaticum leaves.