Abstract
The characteristic secondary metabolites in tea (theanine, caffeine, and catechins) are important factors contributing to unique tea flavors. However, there has been relatively little research on molecular markers related to these metabolites. Thus, we conducted a genome-wide association analysis of the levels of these tea flavor-related metabolites in three seasons. The theanine, caffeine, and catechin levels in Population 1 comprising 191 tea plant germplasms were examined, which revealed that their heritability exceeded 0.5 in the analyzed seasons, with the following rank order (highest to lowest heritabilities): (+)-catechin > (−)-gallocatechin gallate > caffeine = (−)-epicatechin > (−)-epigallocatechin-3-gallate > theanine > (−)-epigallocatechin > (−)-epicatechin-3-gallate > catechin gallate > (+)-gallocatechin. The SNPs detected by amplified-fragment SNP and methylation sequencing divided Population 1 into three groups and seven subgroups. An association analysis yielded 307 SNP markers related to theanine, caffeine, and catechins that were common to all three seasons. Some of the markers were pleiotropic. The functional annotation of 180 key genes at the SNP loci revealed that FLS, UGT, MYB, and WD40 domain-containing proteins, as well as ATP-binding cassette transporters, may be important for catechin synthesis. KEGG and GO analyses indicated that these genes are associated with metabolic pathways and secondary metabolite biosynthesis. Moreover, in Population 2 (98 tea plant germplasm resources), 30 candidate SNPs were verified, including 17 SNPs that were significantly or extremely significantly associated with specific metabolite levels. These results will provide a foundation for future research on important flavor-related metabolites and may help accelerate the breeding of new tea varieties.
Highlights
Introduction Tea originated in southwesternChina and has been cultivated for more than 5000 years[1]
The correlation was relatively strong for TN, CAF, C, EC, EGCG, gallocatechin gallate (GCG), ECG, and catechin gallate (CG) but relatively weak for EGC and CG
We identified 26 pathways associated with GCG, including metabolic pathways, secondary metabolite biosynthesis, flavonoid biosynthesis, aminoacyl-tRNA biosynthesis, purine metabolism, ubiquitin-mediated proteolysis, zeatin biosynthesis, amino acid synthesis and metabolism, and keratin, flax, and wax biosynthesis (Table S7)
Summary
China and has been cultivated for more than 5000 years[1] Because they are used to produce one of the three major nonalcoholic beverages worldwide (the other two being coffee and cocoa), tea plants are economically valuable crops that significantly affect society and culture. Because of the important effects of TN, CAF, and catechins on tea quality and their physiological functions, studies on their synthesis and regulatory pathways are crucial for the development and selection of tea plants with specific TN, CAF, and catechin levels. The presence of genes responsible for target traits can be detected. This process is fast, accurate, and unaffected by material development. It may be applicable for selecting new tea varieties and improving tea breeding efficiency
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