Metabolomic and transcriptomic analyses reveal the biosynthetic mechanisms of pigments and main taste compounds in an albino tea cultivar

Significant variations in leaf colours, pigment contents, and main taste compounds in young shoots from albino tea plants (Camellia sinensis) influence tea flavour. However, the seasonal metabolic pattern and molecular regulatory mechanism of these metabolites remain largely elusive. Herein, we conducted morphological, biochemical, metabolomic and transcriptomic analyses between an albino tea cultivar 'Zhonghuang 3' ('ZH3') and a green strain 'Tai cha 15' ('TC15') at four-time points (April 12, May 31, July 14, and August 17) to elucidate dynamic changes in these compounds and predict the relationships among transcription factors (TFs), target genes (TGs), and metabolite abundance. Generally, leaf colours and pigment contents were significantly lighter and lower, respectively, in 'ZH3' than in 'TC15' from spring to summer, but were subsequently similar. Compared to 'TC15', 'ZH3' had a lower and broader phenol/ammonia ratio as well as stable caffeine content and showed more significantly different metabolites and differentially expressed genes. The relationship between pigments, main taste compounds, and their biosynthetic genes, as well as TFs and their TGs, had genetic specificity. These results suggested that the biosynthesis of these compounds was probably both season- and variety-dependent. In total, 12 models of the TF-TG-metabolite regulatory network were proposed to uncover the biosynthetic and regulatory mechanisms of these metabolites in tea plants. A high correlation was observed between some structural genes and TFs with the accumulation of these metabolites. These findings provide novel insights into the regulatory mechanisms underlying accumulation of pigments and main taste compounds in tea plants.