Identifying key genes involved in yellow leaf variation in 'Menghai Huangye' based on biochemical and transcriptomic analysis.

Albino tea plants generally have higher theanine, which causes their tea leaves to taste fresher, and they are an important mutant for the breeding of tea plant varieties. Earlier, we reported an albino germplasm, 'Menghai Huangye' (MHHY), from Yunnan Province and found that it has a lower chlorophyll content during the yellowing stage, but the mechanism underlying low chlorophyll and the yellowing phenotype is still unclear. In this study, the pigment contents of MHHY_May (yellowing, low chlorophyll), MHHY_July (regreening, normal chlorophyll), and YK10_May (green leaves, normal chlorophyll) were determined, and the results showed that the lower chlorophyll content might be an important reason for the formation of the yellowing phenotype of MHHY. Through transcriptome sequencing, we obtained 654 candidates for differentially expressed genes (DEGs), among which 4 genes were related to chlorophyll synthesis, 10 were photosynthesis-related, 34 were HSP family genes, and 19 were transcription factor genes. In addition, we analysed the transcription levels of the key candidate genes in MHHY_May and MHHY_July and found that they are consistent with the expression trends in MHHY_May and YK10_May, which further indicates that the candidate differential genes we identified are likely to be key candidate factors involved in the low chlorophyll content and yellowing of MHHY. In summary, our findings will assist in revealing the low chlorophyll content of MHHY and the formation mechanism of yellowing tea plants and will be applied to the selection and breeding of albino tea cultivars in the future.

Menghai Huangye, a novel albino tea germplasm with high theanine content and a high catechin index.

Yunnan Province has a very wide diversity of tea germplasm resources. A variety of special tea germplasms with outstanding traits have been discovered, including tea germplasms with high anthocyanin content and low caffeine content. Albino tea cultivars generally have higher contents of theanine that contribute to the umami taste, and the quality of tea brewed from it is higher. The catechin index (CI), the ratio of dihydroxylated catechins (DIC) to trihydroxylated catechins (TRIC), is a crucial index of suitability for processing tea. In this study, the albino tea plant Menghai Huangye (MHHY) with yellow leaves was identified. Analysis of the biochemical components revealed that MHHY was enriched in theanine and the total catechins (TC) were lower than Yunkang 10 (YK10). In addition, the CI value of MHHY was extremely significantly higher than that of YK10. Metabolic profile of catechins and the related gene expression profile analysis found that the coordinated expression of the key branch genes F3'H and F3'5'Ha for the synthesis of DIC and TRIC in tea plant was closely related to the high CI and low TC of MHHY. Further analysis of the F3'H promoter showed that a 284-bp deletion mutation was present in the F3'H promoter of MHHY, containing the binding sites of the transcriptional repressor MYB4 involved in flavonoid metabolism, which might be an important reason for the up-regulated expression of F3'H in MHHY. Overall, this study provides a theoretical basis for understanding the characteristics of albino tea germplasm resources and efficiently utilizing high-CI tea germplasm resources.

Comparative transcriptomic analysis of the tea plant (Camellia sinensis) reveals key genes involved in pistil deletion.

BACKGROUND: The growth process of the tea plant (Camellia sinensis) includes vegetative growth and reproductive growth. The reproductive growth period is relatively long (approximately 1.5 years), during which a large number of nutrients are consumed, resulting in reduced tea yield and quality, accelerated aging, and shortened economic life of the tea plant. The formation of unisexual and sterile flowers can weaken the reproductive growth process of the tea plant. To further clarify the molecular mechanisms of pistil deletion in the tea plant, we investigated the transcriptome profiles in the pistil-deficient tea plant (CRQS), wild tea plant (WT), and cultivated tea plant (CT) by using RNA-Seq. RESULTS: A total of 3683 differentially expressed genes were observed between CRQS and WT flower buds, with 2064 upregulated and 1619 downregulated in the CRQS flower buds. These genes were mainly involved in the regulation of molecular function and biological processes. Ethylene synthesis-related ACC synthase genes were significantly upregulated and ACC oxidase genes were significantly downregulated. Further analysis revealed that one of the WIP transcription factors involved in ethylene synthesis was significantly upregulated. Moreover, AP1 and STK, genes related to flower development, were significantly upregulated and downregulated, respectively. CONCLUSIONS: The transcriptome analysis indicated that the formation of flower buds with pistil deletion is a complex biological process. Our study identified ethylene synthesis, transcription factor WIP, and A and D-class genes, which warrant further investigation to understand the cause of pistil deletion in flower bud formation.