Transcriptomic and biochemical analysis reveal differential regulatory mechanisms of photosynthetic pigment and characteristic secondary metabolites between high amino acids green-leaf and albino tea cultivars

It is generally believed that albino tea cultivars contain high amino acid content, and numerous studies have used them as materials to reveal L-theanine metabolism mechanism. However, few studies on the research of high amino acid green-leaf tea cultivars were reported. Here, high amino acid green-leaf tea cultivars, 'Baojing Huangjincha1' (BJ1) and 'Huangjincha2' (HJC2) have been discovered. In this study, biochemical ingredients and transcriptomes of high amino acids green-leaf tea cultivars (BJ1, HJC2) and albino tea cultivars, 'Baiye1' (BY1) and 'Huangjinya' (HJY) were analyzed and compared. Biochemical analyses showed that the contents of chlorophyll and carotenoids in albino tea cultivars (BY1, HJY) were much lower than that in green-leaf tea cultivars (BJ1, HJC2), whereas increases were noted in the ratio of carotenoids to chlorophyll. The content of catechins was lower in HJC2, BY1 and HJY than that in BJ1. The content of L-theanine also showed considerable variability among four tea cultivars. Especially, HJC2 with dark-green leaves contained the highest L-theanine and lowest catechins content. At transcription level, the results revealed expression patterns of genes related to chlorophyll biosynthesis were significantly up-regulated in HJC2. Suppressed expressions of CsCHS in HJC2, CsPAL in BY1, and CsF3′5′H in HJY were responsible for the lower catechins content, respectively. Furthermore, we also found that CsGOGAT and CsGS/TS were key genes leading to differences in the accumulation patterns of L-theanine between HJC2 and BY1. These findings provide basis for further research on regulatory mechanisms of pigments and characteristic secondary metabolites in tea plants.