Comprehensive Dissection of Metabolic Changes in Albino and Green Tea Cultivars.

Albino tea cultivars are special mutants of tea plants with white or yellow leaf color. In this study, three albino tea cultivars, including 'Anji Baicha', 'Huangjinya', and 'Baijiguan', and two green tea cultivars, 'Longjing 43' and 'Fuding Dabaicha', were applied to metabolite profiling by gas chromatography-mass spectrometry and ultraperformance liquid chromatography-mass spectrometry. Multivariate analyses revealed significantly different metabolite phenotypes in leaves among albino cultivars and green cultivars. The differential metabolite-related pathways included galactose metabolism, tryptophan metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis. For the young leaves of albino cultivars, the sugar (sorbitol and erythrose) and amino acid (mainly proline, isoleucine, ornithine, aspartic acid, threonine, and valine) concentrations increased, whereas gallocatechin and epigallocatechin gallate concentrations decreased. These results reveal the divergence in metabolic profiling between tea plant cultivars with different leaf colors. With the development of leaves, the concentrations of flavonoids increased largely in the older leaves of albino cultivars.

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

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 ß-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.

Small RNA and degradome profiling reveals important roles for microRNAs and their targets in tea plant response to drought stress.

Tea (Camellia sinensis) is a popular beverage worldwide. Drought stress (DS) is a major constraint on the growth, yield and quality of tea plants. MicroRNAs (miRNAs) play important roles in plant responses to DS. We constructed eight small RNA libraries from the drought-tolerant 'Ningzhou 2' (NZ2) and drought-susceptible 'Zhuyeqi' (ZYQ) cultivars during four stages [control (CK), the fourth day of DS, the eighth day of DS and after recovery (RC)]. A total of 268 conserved and 62 novel miRNAs were identified using small RNA sequencing. In total, 139 (52.9%) and 96 (36.0%) conserved miRNAs were differentially expressed during the four stages (P ≤ 0.05) in NZ2 and ZYQ, respectively. A total of 814 predicted target genes were identified as differentially regulated by 199 miRNAs through degradome sequencing. Among them, 201 and 218 genes were specific to the NZ2 and ZYQ cultivars, respectively, and 395 were common to both cultivars. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed the biological roles of these targets and showed that some of the targets responded to DS in a stress- and cultivar-dependent manner. Correlated expression patterns between miRNA and their targets showed that specific miRNAs target the miRNA effector Argonaute 1 (AGO1), drought signaling-related receptors and enzymes, transcription factors, and other structural and functional proteins. The predicted regulatory networks provide insights into a potential miRNA-mediated regulatory mechanism. These results will contribute to the breeding of drought-tolerant tea plants and to elucidating miRNA regulation in response to drought.