Integrative Metabolomic and Transcriptomic Analysis Reveals the Mechanism of Specific Color Formation in Phoebe zhennan Heartwood

Abstract

Nanmu (Phoebe zhennan) is an extremely valuable tree plant that is the main source of famous “golden-thread nanmu” wood. The potential metabolites and gene regulation mechanisms involved in golden thread formation are poorly understood, even though the color change from sapwood to heartwood has been investigated in several tree plants. Here, five radial tissues from sapwood to heartwood were compared via integrative metabolomic and transcriptomic analysis to reveal the secondary metabolites and molecular mechanisms involved in golden thread formation. During heartwood formation, gradual starch grain loss is accompanied by the cell lumen deposition of lipids and color-related extractives. Extractives of 20 phenylpropanoids accumulated in heartwood, including cinnamic acids and derivatives, coumarin acid derivatives, and flavonoids, which were identified as being closely related to the golden thread. Phenylpropanoids co-occurring with abundant accumulated metabolites of prenol lipids, fatty acyls, steroids, and steroid derivatives may greatly contribute to the characteristics of golden thread formation. Additionally, the expression of nine genes whose products catalyze phenylpropanoid and flavonoids biosynthesis was upregulated in the transition zone, then accumulated and used to color the heartwood. The expression levels of transcription factors (e.g., MYB, bHLH, and WRKY) that act as the major regulatory factors in the synthesis and deposition of phenylpropanoid and flavonoids responsible for golden thread formation were also higher than in sapwood. Our results not only explain golden thread formation in nanmu, but also broaden current knowledge of special wood color formation mechanisms. This work provides a framework for future research focused on improving wood color.

Comparative Metabolomics and Transcriptome Analysis Reveal the Fragrance-Related Metabolite Formation in Phoebe zhennan Wood

“…Wei) belongs to the Lauraceae family and Machilus Nees genus and is an evergreen broad-leaved tree. It is a rare species that is endemic to China and mainly distributed in Sichuan, Guizhou, and Hubei [1,2]. Its trunk is straight and graceful, and its crown is tight, making it a famous garden ornamental tree species [3].…”

“…The wood is known as "golden-thread nanmu" due to its dense texture, strong corrosion resistance, and metallic luster, which was the main species of nanmu in the Forbidden City in China [3][4][5][6]. One of the most important characteristics of nanmu is that its wood has a fragrance, which is an important breeding characteristic that reflects the economic and cultural value of nanmu [2]. Furthermore, P. zhennan is a source of wood essential oils, containing volatile organic compounds (VOCs) with high economic value in the spice and perfume industries [7].…”

“…Secondary metabolites are the final products that directly reflect phenotypic and functional changes produced by the plant metabolism driven by gene regulation [2]. Previous studies have demonstrated that heartwood formation and the biosynthesis of secondary metabolites are mainly genetically determined [11].…”

Metabolomics and Transcription Profiling of Pumpkin Fruit Reveals Enhanced Bioactive Flavonoids and Coumarins in Giant Pumpkin (Cucurbita maxima)

“…The expression levels of DEGs involved in flavonoids and coumarins biosynthesis were most likely regulated by co-expressed TF families. 51 Based on the constructed co-expression network and cis-acting element assay in promoters of structural genes, many types of TFs were found to be involved in the regulation of key genes in flavonoids and coumarins biosynthesis, including those that encode MYB, AP2, bHLH, and WRKY. It is well known that these TFs function as regulators in the plant flavonoids biosynthesis pathway.…”

Identification and variation analysis of the composition and content of essential oil and fragrance compounds in Phoebe zhennan wood at different tree ages

“…Nanmu wood is the main source of “golden thread nanmu”, which has high economic value, and harbors EOs. The tree has an attractive visible golden thread pattern, a rich fragrance, and high durability ( Xiao et al., 2020 ; Yang et al., 2022a ). Due to these qualities, P. zhennan wood has become popular for use in furniture, various high-class furnishing materials, cosmetics, health products, among others.…”