Phytohormone and transcriptome of pericarp reveals jasmonate and LcMYC2 are involved in neral and geranial biosynthesis in Litsea cubeba

Litsea cubeba (Lour.) Person (Lauraceae) is a famous essential oil tree that produces L. cubeba essential oil (LCEO) in the pericarp. LCEO, mainly containing neral and geranial (~80%), has been widely used in medical treatment, cosmetics, food and other fields. Knowledge of the development of the L. cubeba pericarp would provide an important basis for LCEO production and genetic breeding. Here, according to the characteristics of the pericarp development process, we provide the phytohormone profiles, including auxin, gibberellin (GA), abscisic acid (ABA), cytokinin (CK), and jasmonate (JA), at 8 timepoints covering the development process of fruit growth, maturation and fruit ripening periods. The results indicated that only the dynamics of JA were consistent with the increasing trend of LCEO, neral, and geranial. Meanwhile, RNA-seq was used to investigate the expression of the genes, especially the genes involved in signal transduction pathways of phytohormones, during L. cubeba pericarp development. The crosstalk among these phytohormone-responsive genes indicated that the hub transcription factor LcMYC2 was also involved in the JA signalling pathway. Furthermore, treatment with MeJA and transient overexpression of LcMYC2 both resulted in significant accumulation of neral and geranial in L. cubeba. Finally, LcMYC2 was verified to promote neral and geranial biosynthesis by transient expression assay, and LcMYC2 enhanced the transcription of LcTPS42 and LcGPPS.SSU1 promoters are key enzymes responsible for the biosynthesis of the above component by yeast one-hybrid (Y1H) and dual-luciferase (dual-LUC) assays. Our data not only provided the profiles of phytohormones and the transcriptome during the development process of the pericarp but also identified the important roles of JA and the hub regulator LcMYC2 in the accumulation of LCEO in the L. cubeba pericarp.