Transcriptome and metabolite analysis reveals key genes for melanin synthesis during the development of Zanthoxylum bungeanum seeds

Abstract

Melanin is a broad term for a family of complex organic macromolecules that contain phenol or indole groups. Melanins are found in animals, plants, and microorganisms and are widely used in medicine, food, and chemical industries. However, at present, the synthesis of plant melanin is still unclear and hinders the development and utilization of melanin. To clarify the composition of plant melanin and the key synthetic genes, we observed the cytological observation of the melanin-forming tissue of ZB seeds and analyzed the transcriptome and metabolite profiles of different developmental stages. We measured seed melanin content and gene expression levels and used redundancy analysis (RDA) to identify key genes that affected melanin synthesis. The seed melanin content was 3.85 % at the green fruit stage (S2) and reached a peak of 4.33 % at the fruit maturity stage (S4). Tyrosine and hydroquinone contents were highest at S2: 830 mg/kg and 77.23 mg/kg, respectively. Catechin, L-epicatechin, procyanidin B1, and p-coumaric acid were the main flavonoids in ZB seeds and reached their highest levels at S2. RDA analysis confirmed that S2 was the key period of melanin synthesis and that ZbPPO, ZbLAR, ZbTYRP1, and ZbTYR had crucial roles in the synthesis of ZB melanin-related substances.