Integration of Metabolome and Transcriptome Reveals the Relationship of Benzenoid–Phenylpropanoid Pigment and Aroma in Purple Tea Flowers

Abstract

Tea (Camellia sinensis) flowers are normally white, even though the leaves could be purple. We previously discovered a specific variety with purple leaves and flowers. In the face of such a phenomenon, researchers usually focus on the mechanism of color formation but ignore the change of aroma. The purple tea flowers contain more anthocyanins, which belong to flavonoids. Meanwhile, phenylalanine (Phe), derived from the shikimate pathway, is a precursor for both flavonoids and volatile benzenoid–phenylpropanoids (BPs). Thus, it is not clear whether the BP aroma was attenuated for the appearance of purple color. In this study, we integrated metabolome and transcriptome of petals of two tea varieties, namely, Zijuan (ZJ) with white flowers and Baitang (BT) with purple flowers, to reveal the relationship between color (anthocyanins) and aroma (volatile BPs). The results indicated that in purple petals, the upstream shikimate pathway promoted for 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHPS) was elevated. Among the increased anthocyanins, delphinidin-3-O-glucoside (DpG) was extremely higher; volatile BPs, including benzyl aldehyde, benzyl alcohol, acetophenone (AP), 1-phenylethanol, and 2-phenylethanol, were also enhanced, and AP was largely elevated. The structural genes related to the biosynthesis of volatile BPs were induced, while the whole flavonoid biosynthesis pathway was downregulated, except for the genes flavonoid 3′-hydroxylase (F3′H) and flavonoid 3′,5′-hydroxylase (F3′5′H), which were highly expressed to shift the carbon flux to delphinidin, which was then conjugated to glucoside by increased bronze-1 (BZ1) (UDP-glucose: flavonoid 3-O-glucosyltransferase) to form DpG. Transcription factors (TFs) highly related to AP and DpG were selected to investigate their correlation with the differentially expressed structural genes. TFs, such as MYB, AP2/ERF, bZIP, TCP, and GATA, were dramatically expressed and focused on the regulation of genes in the upstream synthesis of Phe (DAHPS; arogenate dehydratase/prephenatedehydratase) and the synthesis of AP (phenylacetaldehyde reductase; short-chain dehydrogenase/reductase), Dp (F3′H; F3′5′H), and DpG (BZ1), but inhibited the formation of flavones (flavonol synthase) and catechins (leucoanthocyanidin reductase). These results discovered an unexpected promotion of volatile BPs in purple tea flowers and extended our understanding of the relationship between the BP-type color and aroma in the tea plant.

Transcriptomic and Metabolomic Analyses Provide Insights into the Formation of the Peach-like Aroma of Fragaria nilgerrensis Schlecht. Fruits

“…Therefore, the above-mentioned genes may be important for the formation of the peach-like aroma of F. nilgerrensis fruits. Previous studies revealed that several TFs, such as NAC, ERF, bHLH, MYB, bZIP, TCP, GATA, and HSF family members, help regulate the biosynthesis of fruit flavor-related components [ 42 , 43 , 44 , 45 , 46 ]. Recent research demonstrated that AP2 and FaMYB9 are key TFs that regulate the production of aromatic compounds in strawberry [ 20 , 35 ].…”

Integrating metabolite and transcriptome analysis revealed the different mechanisms of characteristic compound biosynthesis and transcriptional regulation in tea flowers

“…The tea flowering time is approximately during August to October in China, and the tea flowers are usually white. Interestingly, pigmented flowers with purple or pink color were found in some mutation cultivars ( Zhou, C. et al., 2020 ; Mei et al., 2021 ). Purple or pink tea flowers contained abundant anthocyanins compared with white tea flowers.…”

“…Purple or pink tea flowers contained abundant anthocyanins compared with white tea flowers. In the pigmented flowers, anthocyanin substances, including delphinidin-3- O -glucoside, cyanidin O -syringic acid, petunidin 3- O -glucoside, and pelargonidin 3- O -β-d-glucoside, have been identified ( Zhou, C. et al., 2020 ; Mei et al., 2021 ). In purple tea flowers, the contents of many volatiles, including benzyl aldehyde, benzyl alcohol, acetophenone, 1-phenylethanol, and 2-phenylethanol, were also higher than those in white tea flowers ( Mei et al., 2021 ).…”

“…In the pigmented flowers, anthocyanin substances, including delphinidin-3- O -glucoside, cyanidin O -syringic acid, petunidin 3- O -glucoside, and pelargonidin 3- O -β-d-glucoside, have been identified ( Zhou, C. et al., 2020 ; Mei et al., 2021 ). In purple tea flowers, the contents of many volatiles, including benzyl aldehyde, benzyl alcohol, acetophenone, 1-phenylethanol, and 2-phenylethanol, were also higher than those in white tea flowers ( Mei et al., 2021 ). Saponins, which belong to triterpene or steroid glycosides, play crucial roles in terms of health benefits, inducing autophagy and apoptosis in ovarian cancer cells, and inhibiting cancer cell proliferation ( Ghosh et al., 2006 ; Zhao et al., 2015 ; Fan et al., 2019 ; Wang et al., 2020 ).…”

Transcriptome and metabolome reveal key genes in the phenylpropane pathway to regulate the floral fragrance of Rhododendron fortunei

“…The mutation-induced signi cant up-regulation of key genes involved in the anthocyanin synthesis pathway, glycosylation, and chelation, resulted in a signi cant increase in anthocyanin accumulation in mutant rose. Mei et al [25] integrated the metabolome and transcriptome of the petals of two tea plant varieties, white-owered ZJ and pink-owered BT, to reveal the relationship between tea plant color and aroma; that is, the relationship between anthocyanins and benzene/phenylpropanoid VOCs. The results showed that the content of various anthocyanins in BT was higher than that in ZJ, among which delphinidin-3-O-glucoside was very high in BT, and the content of benzene/phenylpropane VOCs including benzaldehyde, benzyl alcohol, acetophenone, 1-phenethyl alcohol and 2-phenethyl alcohol was also higher in BT than in ZJ.…”