Comparative Transcriptome Analysis Identifies Key Regulatory Genes Involved in Anthocyanin Metabolism During Flower Development in Lycoris radiata

Lycoris is used as a garden flower due to the colorful and its special flowers. Floral coloration of Lycoris is a vital trait that is mainly regulated via the anthocyanin biosynthetic pathway. In this study, we performed a comparative transcriptome analysis of Lycoris radiata petals at four different flower development stages. A total of 38,798 differentially expressed genes (DEGs) were identified by RNA sequencing, and the correlation between the expression level of the DEGs and the anthocyanin content was explored. The identified DEGs are significantly categorized into ‘flavonoid biosynthesis,’ ‘phenylpropanoid biosynthesis,’ ‘Tropane, piperidine and pyridine alkaloid biosynthesis,’ ‘terpenoid backbone biosynthesis’ and ‘plant hormone signal transduction’ by Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The candidate genes involved in anthocyanin accumulation in L. radiata petals during flower development stages were also identified, which included 56 structural genes (especially LrDFR1 and LrFLS) as well as 27 key transcription factor DEGs (such as C3H, GATA, MYB, and NAC). In addition, a key structural gene namely LrDFR1 of anthocyanin biosynthesis pathway was identified as a hub gene in anthocyanin metabolism network. During flower development stages, the expression level of LrDFR1 was positively correlated with the anthocyanin content. Subcellular localization revealed that LrDFR1 is majorly localized in the nucleus, cytoplasm and cell membrane. Overexpression of LrDFR1 increased the anthocyanin accumulation in tobacco leaves and Lycoris petals, suggesting that LrDFR1 acts as a positively regulator of anthocyanin biosynthesis. Our results provide new insights for elucidating the function of anthocyanins in L. radiata petal coloring during flower development.

Effect of Exogenous Gibberellin, Paclobutrazol, Abscisic Acid, and Ethrel Application on Bulblet Development in Lycoris radiata

Lycoris species have great ornamental and medicinal values; however, their low regeneration efficiency significantly restricts their commercial production. Exogenous hormone application is an effective way to promote bulblet development, but their effect on Lycoris radiata has not been verified to date. In the present study, we examined the effect of different exogenous hormones on bulblet development in L. radiata, and found that gibberellic acid (GA) significantly inhibited, whereas paclobutrazol (PBZ), abscisic acid (ABA), and ethrel promoted bulblet development, especially PBZ, a GA biosynthesis inhibitor. Furthermore, GA reduced endogenous cytokinin (CK) content, as well as the activities of carbohydrate metabolism enzymes, including sucrose synthase (SUS) and glucose-1-phosphate adenylyltransferase (AGPase), by downregulating the expression levels of LrSUS1, LrSUS2, and genes encoding AGPase large and small subunits. This resulted in the decrease in carbohydrate accumulation in the bulblets, thus hindering their development. PBZ had the opposite effect to GA on carbohydrate metabolism; it decreased endogenous GA15 and GA24, thereby promoting bulblet development. ABA promoted endogenous auxin content and the activities of starch synthesis enzymes, especially soluble starch synthase (SSS) and granule-bound SS (GBSS), through the up-regulation of the expression levels of LrSS1, LrSS2, and LrGBSS1 genes, which could also result in the accumulation of carbohydrates in the bulblets and promote their development. In addition, ethrel application partly promoted bulblet development by promoting endogenous CK content. Although the accumulation of carbohydrates and the activity of starch enzymes were increased by ethrel treatment, we hypothesized that the effect of ethrel on regulating carbohydrate metabolism may be indirect. Our results could provide a basis for improving the propagation efficiency of L. radiata for production, as well as propose some directions for future research.

Metabolic Profiling of Primary Metabolites and Galantamine Biosynthesis in Wounded Lycoris radiata Callus

Plants are continuously exposed to abiotic and biotic factors that lead to wounding stress. Different plants exhibit diverse defense mechanisms through which various important metabolites are synthesized. Humans can exploit these mechanisms to improve the efficacy of existing drugs and to develop new ones. Most previous studies have focused on the effects of wounding stress on the different plant parts, such as leaves, stems, and roots. To date, however, no study has investigated the accumulation of primary and galantamine content following the exposure of a callus to wounding stress. Therefore, in the present study, we exposed Lycoris radiata calli to wounding stress and assessed the expression levels of several genes involved in metabolic pathways at various time points (0, 3, 6, 12, 24, 48, 72, and 96 h of exposure). Furthermore, we quantify the primary and galantamine content using gas chromatography–time-of-flight mass spectrometry and the high-performance liquid chromatography qRT-PCR analysis of eight galantamine pathway genes (LrPAL-2, LrPAL-3, LrC4H-2, LrC3H, LrTYDC2, LrN4OMT, LrNNR, and LrCYP96T) revealed that seven genes, except LrN4OMT, were significantly expressed following exposure to wounding stress. Galantamine contents of calli after 3, 6, 12, 24, 48, 72, and 96 h of exposure were respectively 2.5, 2.5, 3.5, 3.5, 5.0, 5.0, and 8.5 times higher than that after 0 h of exposure. Furthermore, a total of 48 hydrophilic metabolites were detected in the 0 h exposed callus and 96 h exposed callus using GC-TOFMS. In particular, a strong positive correlation between galantamine and initial precursors, such as phenylalanine and tyrosine, was observed.