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Biochemical and transcriptomic analyses reveal different metabolite biosynthesis profiles among three color and developmental stages in ‘ Anji Baicha ’ ( Camellia sinensis )

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ABSTRACT

Background: The new shoots of the albino tea cultivar ‘Anji Baicha’ are yellow or white at low temperatures and turn green as the environmental temperatures increase during the early spring. ‘Anji Baicha’ metabolite profiles exhibit considerable variability over three color and developmental stages, especially regarding the carotenoid, chlorophyll, and theanine concentrations. Previous studies focused on physiological characteristics, gene expression differences, and variations in metabolite abundances in albino tea plant leaves at specific growth stages. However, the molecular mechanisms regulating metabolite biosynthesis in various color and developmental stages in albino tea leaves have not been fully characterized.

Results: We used RNA-sequencing to analyze ‘Anji Baicha’ leaves at the yellow-green, albescent, and re-greening stages. The leaf transcriptomes differed considerably among the three stages. Functional classifications based on Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that differentially expressed unigenes were mainly related to metabolic pathways, biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, and carbon fixation in photosynthetic organisms. Chemical analyses revealed higher β-carotene and theanine levels, but lower chlorophyll a levels, in the albescent stage than in the green stage. Furthermore, unigenes involved in carotenoid, chlorophyll, and theanine biosyntheses were identified, and the expression patterns of the differentially expressed unigenes in these biosynthesis pathways were characterized. Through co-expression analyses, we identified the key genes in these pathways. These genes may be responsible for the metabolite biosynthesis differences among the different leaf color and developmental stages of ‘Anji Baicha’ tea plants.

Conclusions: Our study presents the results of transcriptomic and biochemical analyses of ‘Anji Baicha’ tea plants at various stages. The distinct transcriptome profiles for each color and developmental stage enabled us to identify changes to biosynthesis pathways and revealed the contributions of such variations to the albino phenotype of tea plants. Furthermore, comparisons of the transcriptomes and related metabolites helped clarify the molecular regulatory mechanisms underlying the secondary metabolic pathways in different stages.

Electronic supplementary material: The online version of this article (doi:10.1186/s12870-016-0885-2) contains supplementary material, which is available to authorized users.

No MeSH data available.


Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment of differentially expressed unigenes. a Top 15 KEGG pathways containing the most differentially expressed unigenes. b Top 15 KEGG pathways containing the greatest percentage of up-regulated unigenes from the yellow-green (YG) stage to the albescent (W) stage, and from the W stage to the re-greening (G) stage. c Top 15 KEGG pathways containing the greatest percentage of down-regulated unigenes from the YG stage to the W stage, and from the W stage to the G stage. The percentages were calculated relative to the total number of unigenes for a given KEGG pathway
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Fig3: Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment of differentially expressed unigenes. a Top 15 KEGG pathways containing the most differentially expressed unigenes. b Top 15 KEGG pathways containing the greatest percentage of up-regulated unigenes from the yellow-green (YG) stage to the albescent (W) stage, and from the W stage to the re-greening (G) stage. c Top 15 KEGG pathways containing the greatest percentage of down-regulated unigenes from the YG stage to the W stage, and from the W stage to the G stage. The percentages were calculated relative to the total number of unigenes for a given KEGG pathway

Mentions: The DEGs between each pair of stages were enriched in genes related to distinct KEGG pathways (Fig. 3). The top 15 KEGG pathways corresponding to the most abundant DEGs are presented in Fig. 3a. With the color and developmental changes in leaves from the YG stage to the W stage and then to the G stage, the KEGG pathways that were enriched in DEGs remained essentially unchanged. The shared KEGG pathways for the YG vs W, W vs G, and YG vs G comparisons included metabolic pathways, biosynthesis of secondary metabolites, starch and sucrose metabolism, phenylpropanoid biosynthesis, purine metabolism, carbon fixation in photosynthetic organisms, and glycolysis or gluconeogenesis. The most abundant up- (Fig. 3b) or down-regulated (Fig. 3c) DEGs between two consecutive stages were assigned to 15 individual KEGG pathways. The common up-regulated KEGG pathways for the W vs YG and G vs W comparisons were related to photosynthesis, carotenoid biosynthesis, nitrogen metabolism, pentose phosphate pathway, and sulfur metabolism. The common down-regulated KEGG pathways for the W vs YG and G vs W comparisons were associated with ribosomes, gap junctions, and anthocyanin biosynthesis.Fig. 3


Biochemical and transcriptomic analyses reveal different metabolite biosynthesis profiles among three color and developmental stages in ‘ Anji Baicha ’ ( Camellia sinensis )
Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment of differentially expressed unigenes. a Top 15 KEGG pathways containing the most differentially expressed unigenes. b Top 15 KEGG pathways containing the greatest percentage of up-regulated unigenes from the yellow-green (YG) stage to the albescent (W) stage, and from the W stage to the re-greening (G) stage. c Top 15 KEGG pathways containing the greatest percentage of down-regulated unigenes from the YG stage to the W stage, and from the W stage to the G stage. The percentages were calculated relative to the total number of unigenes for a given KEGG pathway
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Fig3: Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment of differentially expressed unigenes. a Top 15 KEGG pathways containing the most differentially expressed unigenes. b Top 15 KEGG pathways containing the greatest percentage of up-regulated unigenes from the yellow-green (YG) stage to the albescent (W) stage, and from the W stage to the re-greening (G) stage. c Top 15 KEGG pathways containing the greatest percentage of down-regulated unigenes from the YG stage to the W stage, and from the W stage to the G stage. The percentages were calculated relative to the total number of unigenes for a given KEGG pathway
Mentions: The DEGs between each pair of stages were enriched in genes related to distinct KEGG pathways (Fig. 3). The top 15 KEGG pathways corresponding to the most abundant DEGs are presented in Fig. 3a. With the color and developmental changes in leaves from the YG stage to the W stage and then to the G stage, the KEGG pathways that were enriched in DEGs remained essentially unchanged. The shared KEGG pathways for the YG vs W, W vs G, and YG vs G comparisons included metabolic pathways, biosynthesis of secondary metabolites, starch and sucrose metabolism, phenylpropanoid biosynthesis, purine metabolism, carbon fixation in photosynthetic organisms, and glycolysis or gluconeogenesis. The most abundant up- (Fig. 3b) or down-regulated (Fig. 3c) DEGs between two consecutive stages were assigned to 15 individual KEGG pathways. The common up-regulated KEGG pathways for the W vs YG and G vs W comparisons were related to photosynthesis, carotenoid biosynthesis, nitrogen metabolism, pentose phosphate pathway, and sulfur metabolism. The common down-regulated KEGG pathways for the W vs YG and G vs W comparisons were associated with ribosomes, gap junctions, and anthocyanin biosynthesis.Fig. 3

View Article: PubMed Central - PubMed

ABSTRACT

Background: The new shoots of the albino tea cultivar ‘Anji Baicha’ are yellow or white at low temperatures and turn green as the environmental temperatures increase during the early spring. ‘Anji Baicha’ metabolite profiles exhibit considerable variability over three color and developmental stages, especially regarding the carotenoid, chlorophyll, and theanine concentrations. Previous studies focused on physiological characteristics, gene expression differences, and variations in metabolite abundances in albino tea plant leaves at specific growth stages. However, the molecular mechanisms regulating metabolite biosynthesis in various color and developmental stages in albino tea leaves have not been fully characterized.

Results: We used RNA-sequencing to analyze ‘Anji Baicha’ leaves at the yellow-green, albescent, and re-greening stages. The leaf transcriptomes differed considerably among the three stages. Functional classifications based on Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that differentially expressed unigenes were mainly related to metabolic pathways, biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, and carbon fixation in photosynthetic organisms. Chemical analyses revealed higher β-carotene and theanine levels, but lower chlorophyll a levels, in the albescent stage than in the green stage. Furthermore, unigenes involved in carotenoid, chlorophyll, and theanine biosyntheses were identified, and the expression patterns of the differentially expressed unigenes in these biosynthesis pathways were characterized. Through co-expression analyses, we identified the key genes in these pathways. These genes may be responsible for the metabolite biosynthesis differences among the different leaf color and developmental stages of ‘Anji Baicha’ tea plants.

Conclusions: Our study presents the results of transcriptomic and biochemical analyses of ‘Anji Baicha’ tea plants at various stages. The distinct transcriptome profiles for each color and developmental stage enabled us to identify changes to biosynthesis pathways and revealed the contributions of such variations to the albino phenotype of tea plants. Furthermore, comparisons of the transcriptomes and related metabolites helped clarify the molecular regulatory mechanisms underlying the secondary metabolic pathways in different stages.

Electronic supplementary material: The online version of this article (doi:10.1186/s12870-016-0885-2) contains supplementary material, which is available to authorized users.

No MeSH data available.