Identification of Yellow Pigmentation Genes in Brassica rapa ssp. pekinensis Using Br300 Microarray

Preliminary Analysis of the Formation Mechanism of Floret Color in Broccoli (Brassica oleracea L var. italica) Based on Transcriptomics and Targeted Metabolomics

Floret color is a crucial phenotypic trait in broccoli, serving as an indicator of maturity and determining its market value. However, the mechanisms underlying color variation remain unclear. In this study, six broccoli varieties with different floret colors at harvest were chosen as materials. The color difference and pigment content of florets were measured, and a combined analysis of anthocyanin-targeted metabolome and transcriptome was conducted. Our findings revealed that chlorophyll a primarily influences green, yellow-green, and light green coloration, while the wax content may contribute to gray-green coloration. The blue-green and dark blue-green coloration are regulated by both chlorophyll a and anthocyanins. Targeted metabolomics identified five anthocyanin compounds, with peonidin-3-O-glucoside as a key metabolite for blue-green coloration and delphinidin-3-O-glucoside-5-O-galactoside and peonidin-3,5-O-diglucoside for dark blue-green coloration. Transcriptomic analysis identified CHLG as a potential key regulator for yellow-green and light-green floret coloration. The blue-green coloration appears to be coregulated by a combination of genes, including the chlorophyll biosynthesis gene HEMF; anthocyanin biosynthesis genes (PAL, FLS, and UGT); and chlorophyll degradation genes (SGR, PPD, and NYC). Furthermore, upstream genes involved in both chlorophyll metabolism (CHLI, CHLD, CHLM, DVR, and CLH) and anthocyanin biosynthesis (PAL, 4CL, CHS, F3'H, and FLS) play crucial roles in determining the dark blue-green coloration of florets. Meanwhile, transcription factors of the WRKY, NAC, and TCP families are involved in chlorophyll metabolism, while those of the bHLH and MYB families participate in anthocyanin synthesis. The WGCNA identified one Hub gene for chlorophyll metabolism and two for anthocyanin synthesis. In conclusion, 35 candidate genes were identified, including 21 involved in chlorophyll metabolism and 14 in anthocyanin biosynthesis. This study provides novel insights into the molecular mechanisms of floret coloration and establishes a foundation for molecular breeding in broccoli.

Recent Advancements and Biotechnological Implications of Carotenoid Metabolism of Brassica

Carotenoids were synthesized in the plant cells involved in photosynthesis and photo-protection. In humans, carotenoids are essential as dietary antioxidants and vitamin A precursors. Brassica crops are the major sources of nutritionally important dietary carotenoids. Recent studies have unraveled the major genetic components in the carotenoid metabolic pathway in Brassica, including the identification of key factors that directly participate or regulate carotenoid biosynthesis. However, recent genetic advances and the complexity of the mechanism and regulation of Brassica carotenoid accumulation have not been reviewed. Herein, we reviewed the recent progress regarding Brassica carotenoids from the perspective of forward genetics, discussed biotechnological implications and provided new perspectives on how to transfer the knowledge of carotenoid research in Brassica to the crop breeding process.

Transcriptome profiling of yellow leafy head development during the heading stage in Chinese cabbage (Brassica rapa subsp. pekinensis)

The yellow leafy head of Brassica rapa is known to be tasty and nutritional. Therefore, the heading stage of leaf development is critical to realize high yield and economic benefits. A widely planted commercial cultivar of B. rapa ('Qiubao', deep yellow leafy head) was used to conduct transcriptome analysis. The results showed that the yellowing of the inner leaf was likely induced by the predominant β-carotene biosynthesis pathway due to the upregulated gene geranylgeranyl diphosphate and phytoene synthase, and the downregulated gene CrtL-e, NCED4 and DWARF-27. Some genes related to chlorophyll synthesis were also found to be downregulated, such as nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase and protochlorophyllide reductase A. Transcript profiling also revealed strong changes in expression levels of hormonal genes related to auxin, cytokinin, ethylene, abscisic acid, gibberellin and brassinosteroids, suggesting the crucial role that hormones play in heading stage. Examination of carbohydrate and sucrose metabolism pathways revealed that sucrose biosynthesis is probably regulated by 6-phosphofructokinase and sucrose synthase 1 (SUS1/SuSy1) branch, instead of the sucrose-phosphate synthase branch. Several cold-response genes were induced in the late-heading stage, but the results suggest that the common C-repeat binding factor responsive pathway may not be involved in cold adaption. We also identified a series of upregulated transcription factors-AP2/ERF, MYB, bHLH, NAC and WRKY were found to be predominant. The transcripts analysis provides a preliminary genetic resource to unravel key genes and molecular mechanisms responsible for leafy head development in B. rapa, therefore, improving leafy head quality and yield through genetic means in future.

Metabolic Profiling in Chinese Cabbage (Brassica rapa L. subsp. pekinensis) Cultivars Reveals that Glucosinolate Content Is Correlated with Carotenoid Content

A total of 38 bioactive compounds, including glucosinolates, carotenoids, tocopherols, sterols, and policosanols, were characterized from nine varieties of Chinese cabbage (Brassica rapa L. subsp. pekinensis) to determine their phytochemical diversity and analyze their abundance relationships. The metabolite profiles were evaluated with principal component analysis (PCA), Pearson correlation analysis, and hierarchical clustering analysis (HCA). PCA and HCA identified two distinct varieties of Chinese cabbage (Cheonsangcheonha and Waldongcheonha) with higher levels of glucosinolates and carotenoids. Pairwise comparisons of the 38 metabolites were calculated using Pearson correlation coefficients. The HCA, which used the correlation coefficients, clustered metabolites that are derived from closely related biochemical pathways. Significant correlations were discovered between chlorophyll and carotenoids. Additionally, aliphatic glucosinolate and carotenoid levels were positively correlated. The Cheonsangcheonha and Waldongcheonha varieties appear to be good candidates for breeding because they have high glucosinolate and carotenoid levels.