Combined Metabolomic and Transcriptomic Analysis Reveals Candidate Genes for Anthocyanin Accumulation in Ginkgo biloba Seed Exocarp

Anthocyanin is an important pigment that affects plant color change. In this study, the color parameters and anthocyanin content of Ginkgo biloba seed exocarp at different periods were measured, and it was determined that the a* value (redness value) of the seed exocarp was closely related to the color change occurring during the development of the seed exocarp, and the anthocyanin content in the seed exocarp showed an increasing trend. The molecular mechanism of anthocyanin biosynthesis in Ginkgo biloba seed exocarp is still unclear. In order to further understand the molecular mechanism of color change in Ginkgo biloba seed exocarp, the regulation mechanism and accumulation mode of anthocyanin in the seed exocarp at three different periods were analyzed using transcriptomic and metabolomic. A total of four key anthocyanins were screened from the metabolome, including three kinds of Cyanidin 3-arabinoside, Malvidin 3-glucoside and Cyanidin 3-sambubioside 5-glucoside with increased content. Among them, Cyanidin 3-arabinosidehad a strong correlation with the a* value (PCC = 0.914), which have a great influence on the color change of the seed exocarp, and Delphinidin 3-O-3″,6″-O-dimalonylglucoside with decreased content might jointly affect the formation of exocarp color. The transcriptome data show that among the structural genes, ANS (Gb_33402) had the highest correlation with Cyanidin 3-arabinoside (PCC = 0.9217) and in GbANS, only Gb_33402 showed an upregulated expression trend in the three stages of seed exocarp development, which suggesting that it plays an important role in anthocyanin accumulation in the seed exocarp and it may be the key structural gene affecting the formation of seed exocarp color. Among the transcription factors, the differential expression of most transcription factors (MYB, bHLH, b-ZIP, NAC, WDR and AP2/ERF) may jointly affect the formation of seed exocarp color by promoting anthocyanin accumulation. This study elucidates the main anthocyanins that cause the color change of the seed exocarp of Ginkgo biloba and reveals the molecular regulation mechanism of anthocyanins at different developmental stages of the seed exocarp. It provides a theoretical basis and insights for understanding the color change of Ginkgo biloba seed exocarp.