Physiological,Biochemical Characteristics And Molecular Albinism Of The Albino Tea(Camellia Sinensis) Plant

Albino tea plant is a kind of rare tea germplasm resource, which grows albino shoots due to a lack of chlorophyll under a specific environment conditions. These albino shoots have different leaf color, including white, milky white, pale yellow and gold yellow, depending on their concentration of pigments. There are two types of albino tea cultivars:viz. temperature-sensitive albino tea plant and light-sensitive albino tea plant. The albino shoots usually have high level of amino acids and medium levels of polyphenols and caffeine. Therefore, these tea shoots are suitable for processing quality green tea. However, albino phenotypes of the new shoots vary with environment conditions, such as temperature or sunlight intensity, leading to unstable chemical compositions. The albino tea plants have poor resistance to environmental stress, resulting in low survival rate of transplanting and management difficulties of seedling. The radical reason is that the potential mechanism of albinism of the albino tea is not fully understood and then it is difficult to establish corresponding measures to control them. Albino leaves of temperature-sensitive albino tea cultivar’Xiaoxueya’and light-sensitive albino tea cultivar’Huangjinya’were used as the experimental materials to investigate the chloroplast structure by transmission electron microscope, to determine the pigments contents by HPLC, to analyze the contents of tea polyphenols, amino acids, catechins and caffeine by spectrophotometer colorimetric methods or HPLC, to explore the differentially expressed genes by transcriptome and digital gene expression profiling using high-throughput sequencing technology as well as to reveal expression patterns of genes involving in the MEP metabolic pathway, carotenoid metabolic pathway, chlorophyll metabolic pathway and encoding for light-harvesting chlorophyll a/b binding protein by quantitative real-time PCR. The aims of this study were to reveal the physiological and biochemical characteristics as well as the molecular mechanism underlying the albino phenotype of the albino tea cultivars. The major results were summarized as follows:1. Compared to the green bud and leaf of temperature-sensitive albino tea plant ’Xiaoxueya’, the albino leaf had abnormal chloroplast with volume expansion and cystic vacuoles, the suppressed development of grana lamella and thylakoid membranes, as well as the reduced contents of chlorophylls and carotenoids. The albino leaf had high level of amino acids. low levels of tea polyphenols, caffeine, total catechins, EGCG and ECG, resulting in a low ratio of tea polyphenols to amino acids, suggesting it is a good material for high-quality green tea.2. Tea transcriptome was established using temperature-sensitive albino tea cultivar ’Xiaoxueya’and normal tea cultivar "Fudingdabaicha’as the experimental materials, in which there were79797tea unigenes, including11371unigenes with sequence length more than1000bp. The sequences were well assembled with N50length of847bp and average sequencing length of560.30bp. There were6439unigenes, which had simple repeat sequences, and51491unigenes, which were functionally annotated.3. Compared to the green bud and leaf of’Xiaoxueya’, the expression levels of1-deoxy-D-xylulose-5-phosphate synthase gene DXS1and DXS1as well as protochlorophyllide reductase gene Porl and Por2in albino leaf were significantly inhibited. It was considered that the suppressed expression of these key genes led to the shortage of chlorophylls and carotenoids, which might result in the inhibited expression of light-harvesting chlorophyll a/b binding proteins genes Lhcbl-2and Lhcb7through feedback regulation and finally induced hypoplasia of chloroplasts by suppressing the development of thylakoids and grana stacking.4. Light-sensitive albino tea plant ’Huangjinya’grows albino shoots under high temperature and strong sunlight conditions in summer, and the albino leaf can turn green by sunshade treatment. Compared to’Huangjinya’ grown under shading conditions and ’Fudingdabaicha’, the development of thylakoids and grana in chloroplast of’Huangjinya’were hampered under strong sunshine conditions in summer, with reduced level of chlorophylls and increased contents of violaxanthin, lutein and total carotenoids. The accumulation of carotenoids, including violaxanthin and lutein were considered to cause the yellow color of the albino shoots of tea cultivar’Huangjinya’.5. Compared to normal tea cultivars of’Fudingdabaicha’and’Jiukeng’, albino shoots of ’Huangjinya’in spring had high levels of caffeine and amino acids, medium levels of tea polyphenols, catechins and EGCG, low ratio of tea polyphenols to amino acids. While compared to’Fudingdabaicha’ in summer, albino shoots of’Huangjinya’had high level of amino acids, low levels of tea polyphenols, catechins, EGCG and ECG as well as low ratio of tea polyphenols to amino acids. The caffeine concentration in shoots of’Huangjinya’was increased by sunshade treatment in summer.6. Digital gene expression profile was established using shoots with two leaves and a bud of Huangjinya’grown under natural sunshine and sunshade treatment, which there were1392differentially expressed genes were screened and1105genes were functionally annotated. The early light-induced protein gene ELIP was strongly expressed but the expression levels of1-deoxy-D-xylulose-5-phosphate synthase gene family DXS and photosynthetic system II10kDa protein gene psbR were down-regulated in shoots of’Huangjinya’grown under natural strong sunlight conditions. These suggested that’Huangjinya’undergone the light stress under strong sunlight, the biosynthesis of precursors of pigments and the formation of oxygen evolving complex in photosynthetic system Ⅱ of chloroplast in albino leaf of’Huangjinya’were hampered, resulting in abnormality of chlorophyll biosynthesis and chloroplast structure.7. Quantitative real-time PCR results showed that the significantly suppressed expression of1-deoxy-D-xyIulose-5-phosphate synthase gene DXS1, DXS2, DXS3and magnesium chelatase subunit D gene CHLD as well as the high expression of phytoene synthase gene PSY, lycopene p-cyclase gene LCYB, carotene s-monooxygenase gene LUT1, zeaxanthin epoxidase gene ZEP and violaxanthin de-epoxidase gene VDE in albino shoots of’Huangjinya’under strong sunlight might resulted in the reduced concentration of chlorophylls and the high levels of total carotenoids, violaxanthin and lutein, these the fundamental reasons that caused the albino shoots in yellow color of tea cultivar’Huangjinya’. The inhibited expression of light-harvesting complex I chlorophyll a/b binding protein gene Lhca2-2was considered to be induced by the feedback regulation, which suppressed the formation of the chloroplast membrane systems.