The Molecular Mechanism Research In Tea Variegated-Mutant(Camellia Sinensis Cv. Yanling Huayecha)

Tea plant(Camellia sinensis(L.)O.kuntze.)is one of the important economic crops in China,and its leaf color importantly affects the quality of tea.Yanling Huayecha is a variegated tea plant,which shows white and green,and its leaf color performance does not change with environmental changes.There are abundant Studied of variation in plants and focuses on the color mechanism of variation and chloroplast development,but still few studies on the variegation of tea plant is studied.Variations in tea plant changes the content of theanine,a special metabolite.Full of special quality and efficacy,theanine has attracted people’s attention.The accumulation mechanism of theanine is still unclear,It is of great significance to study the coloring mechanism and its correlation with theanine accumulation.In this study,the variegated tea plant Yanling Huayecha was used as the experimental material.According to the difference in leaf color,its leaves were divided into Albino area(AA),Transition site(TS),and Normal part(NP).Here,we investigated the phenotype,physiology and biochemistry and transcriptome sequencing of different parts of the leaf color to explore the possible causes between color mechanism and theanine accumulation,and provide new ideas for the study of theanine accumulation mechanism of tea plant.The main results are as follows:(1)We sequenced the transcriptomes of different leaf color parts and compared the genomes of Chinese tea plants,a total of 44908 unigenes were identified in different color leaf of Yanling Huayecha.There are 2760 significantly different genes in AA than NP,1484 significantly different genes in AA than TS,and 1283 significantly different genes in NP than TS.KEGG enrichment analysis showed that carbon metabolism and amino acid biosynthesis enriched the most differential genes.The change in leaf color causes the content of AA theanine to increase,and the nitrogen metabolism of tea trees is closely related to theanine metabolism.According to the content of AA theanine is changed as the leaf color,and the nitrogen metabolism of tea plant is closely related to theanine metabolism,we pay more attention to these metabolic pathways: Photosynthesis-antenna proteins,porphyrin and chlorophyll metabolism,nitrogen metabolism,biosynthesis of amino acids and alanine,aspartate and glutamate metabolism.We found ten genes related to the coloring mechanism and theanine accumulation,and analyses correlation of genes with phenotype and morphological characteristics and biochemical performance.(2)We conducted photosynthetic pigments and ultrastructural analysis of different leaf color parts,and reported a sudden decrease in pigment content,chloroplast ultrastructure shape elongate,reduced number of grana,not obvious of the grana lamella,vacuoles increased in The NP,TS and AA,and transcription of light-harvesting complex(LHC Ⅱ)overall expression down-regulated.We speculate that this down-regulated expression is accompanied by protein degradation of LHCⅡ.This series of reactions may be a variegated tea plant in order to protect itself from photochemical damage.CP24,CP29,PPOX,PORA played an important role in maintaining the structure of LHCⅡ and ensuring the stacking of thylakoid.The low expression level of CP24 in AA may cause the thylakoid membrane decomposition.(3)We measured the biochemical composition of different leaf color parts,NP,TS and AA showed an increasing trend of total free amino acids and theanine content,the total free amino acid of AA reaches 6.01%,and theanine content is 2.47%.Theanine in AA is 1.25 times of NP,glutamic acid is 1.88 times of NP,and alanine in AA is 2.00 times of NP.The protein degradation of LHCⅡgenerates a large number of amino acid residues,which caused the increase of overall amino acid.Transcriptome sequencing results show there is no difference in the expression of CsTS in AA and NP,but the expression of the two is significantly higher than that of TS.CsTS acts on ethylamine and glutamic acid to synthesize theanine.CsGS1.2 acts on glutamic acid to synthesize glutamine.CsGDH is glutamate dehydrogenase,which acts on glutamate dehydrogenation.CsALAAT2 is an alanine aminotransferase gene that acts on L-alanine to produce pyruvate.The low expression of these genes reversely promotes the accumulation of glutamate and alanine,L-alanine accumulation can enhance the stability of L-alanine dehydrogenase and promote the formation of ethylamine,and the effectiveness of ethylamine is the reason for the difference in the accumulation of L-theanine between tea plants and other plants,The combined effect of these three genes may promote theanine accumulation.