Abstract
The tea cultivar ‘Xiaoxueya’, a temperature-sensitive albino mutant, is a rare tea germplasm because of its highly enriched amino acid content and brisk flavour. In comparison with green leaf tissues of ‘Xiaoxueya’, albino leaves show significant deficiency in chlorophylls and carotenoids and severely disrupted chloroplasts. Furthermore, the accumulation of quality-related secondary metabolites is altered in ‘Xiaoxueya’ albino leaf, with significantly increased contents of total amino acids, theanine, and glutamic acid and significantly decreased contents of alkaloids, catechins, and polyphenols. To uncover the molecular mechanisms underlying albinism and quality-related constituent variation in ‘Xiaoxueya’ leaves, expression profiles of pivotal genes involved in the biosynthetic pathways of pigments, caffeine, theanine, and catechins were investigated by quantitative real-time PCR technology. The results revealed that suppressed expression of the chloroplast-localized 1-deoxy-D-xylulose-5-phosphate synthase genes DXS1 and DXS2 involved in the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway and protochlorophyllide oxidoreductase genes POR1 and POR2 involved in the chlorophyll biosynthetic pathway is responsible for the pigment deficiency in ‘Xiaoxueya’ albino leaf. Additionally, the low expression of the tea caffeine synthase gene (TCS) involved in caffeine biosynthesis and the chalcone synthase genes CHS1, CHS2, and CHS3, the chalcone isomerase gene CHI, the flavonoid 3’,5’-hydroxylase genes F3’5’H1 and F3’5’H2, and the anthocyanidin reductase genes ANR1 and ANR2 involved in the flavonoid pathway is related to the reduction in alkaloid and catechin levels in ‘Xiaoxueya’ albino leaves.
Highlights
The tea plant (Camellia sinensis) is a perennial evergreen woody plant, and its shoots are utilized as raw materials for manufacturing various types of tea products, such as green tea, black tea, and oolong tea
‘White leaf No.1’ was the first temperature-sensitive albino tea cultivar used in China, and it has been widely grown in Zhejiang, Jiangsu, and Guizhou provinces
The young leaves produced when the environmental temperature is below 20°C in early spring are pale yellow or white in colour (Figures 1A, G), whereas the new leaves produced when the temperature increases to above 20°C in the late spring become greener in colour (Figures 1B–F)
Summary
The tea plant (Camellia sinensis) is a perennial evergreen woody plant, and its shoots are utilized as raw materials for manufacturing various types of tea products, such as green tea, black tea, and oolong tea. These tea products, especially green tea, have attracted great attention worldwide for their umami taste, fresh aroma, and health benefits (Butt and Sultan, 2009; Steinmann et al, 2013). The contents of amino acids, including theanine, were found to be significantly higher in young albino shoots of ‘White leaf No.1’ than in normal tea cultivars with green leaves (Du et al, 2006; Li et al, 2016b). The level of protein succinylation/acetylation in ‘White leaf No.1’ is considered to be related to photosynthesis, carbon fixation, amino acid biosynthesis, and porphyrin and chlorophyll metabolism (Xu et al, 2017a; Xu et al, 2017b)
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