Biochemical and Comparative Transcriptome Analyses Reveal Key Genes Involved in Major Metabolic Regulation Related to Colored Leaf Formation in Osmanthus fragrans ‘Yinbi Shuanghui’ during Development

Abstract

Osmanthus fragrans ‘Yinbi Shuanghui’ not only has a beautiful shape and fresh floral fragrance, but also rich leaf colors that change, making the tree useful for landscaping. In order to study the mechanisms of color formation in O. fragrans ‘Yinbi Shuanghui’ leaves, we analyzed the colored and green leaves at different developmental stages in terms of leaf pigment content, cell structure, and transcriptome data. We found that the chlorophyll content in the colored leaves was lower than that of green leaves throughout development. By analyzing the structure of chloroplasts, the colored leaves demonstrated more stromal lamellae and low numbers of granum thylakoid. However, there was a large number of plastoglobuli. Using transcriptome sequencing, we demonstrated that the expression of differentially expressed genes (DEGs) involved in chlorophyll degradation was upregulated, i.e., heme oxygennase-1 (HO1), pheophorbide a oxidase (PAO), and chlorophyllase-2 (CLH2), affecting the synthesis of chlorophyll in colored leaves. The stay-green gene (SGR) was upregulated in colored leaves. Genes involved in carotenoid synthesis, i.e., phytoene synthase 1 (PSY1) and 1-Deoxyxylulose-5-phosphate synthase (DXS), were downregulated in colored leaves, impeding the synthesis of carotenoids. In the later stage of leaf development, the downregulated expression of Golden2-Like (GLK) inhibited chloroplast development in colored leaves. Using weighted gene co-expression network analysis (WGCNA) to investigate the correlation between physiological indicators and DEGs, we chose the modules with the highest degree of relevance to chlorophyll degradation and carotenoid metabolism. A total of five genes (HSFA2, NFYC9, TCP20, WRKY3, and WRKY4) were identified as hub genes. These analyses provide new insights into color formation mechanisms in O. fragrans ‘Yinbi Shuanghui’ leaves at the transcriptional level.

New Insights into the Roles of Osmanthus Fragrans Heat-Shock Transcription Factors in Cold and Other Stress Responses

“…The members of the HSF gene family have been identified from many plant species; however, O. fragrans has 46 HSF genes, which is greater than those in many woody plants, such as P. trichocarpa (28) and M. domestica (25). There is also a large number of segmental duplications in the OfHSFs and a pair of tandem duplication events on the same chromosome (OfHSF41/42) (Figure S2).…”

“…The AHA motifs have transcriptional activation functions, and the number of AHA motifs in an HSF affects the activation activity [9]. The HSFs have been identified in many woody plants, such as Pyrus bretschneideri (29), Malus domestica (25) and Populus trichocarpa (31) [10][11][12]. However, the HSF family members of O. fragrans have not been identified.…”

“…Osmanthus fragrans is an important ornamental and economic woody plant that is widely used in landscaping; however, its application range is greatly limited by cold weather [25]. Studies of O. fragrans have been mainly concerned with fragrance and petal color, and there are also some physiological research on the tolerance of O. fragrans to different stresses [26][27][28][29].…”

Integrated transcriptome and endogenous hormone analysis provides new insights into callus proliferation in Osmanthus fragrans

“…The mapped reads of each sample were assembled by using String Tie version 1.3.1 ( http://ccb.jhu.edu/software/stringtie/ ) in a reference-based approach 54 , 55 . For each gene, the expression level was measured by fragments per kilobase exon model per million mapped fragments (FPKM), based on the number of uniquely mapped reads, to eliminate the influence of different gene lengths and sequencing discrepancies in the gene expression calculation 3 .…”

“…Through a long evolution, O . fragrans has been divided into five groups 3 . In our previous research, the genome of O .…”