Comparative transcriptome analysis reveals key pathways and genes involved in trichome development in tea plant (Camellia sinensis).

Trichomes, which develop from epidermal cells, are considered one of the important characteristics of the tea plant [Camellia sinensis (L.) O. Kuntze]. Many nutritional and metabolomic studies have indicated the important contributions of trichomes to tea products quality. However, understanding the regulation of trichome formation at the molecular level remains elusive in tea plants. Herein, we present a genome-wide comparative transcriptome analysis between the hairless Chuyeqi (CYQ) with fewer trichomes and the hairy Budiaomao (BDM) with more trichomes tea plant genotypes, toward the identification of biological processes and functional gene activities that occur during trichome development. In the present study, trichomes in both cultivars CYQ and BDM were unicellular, unbranched, straight, and soft-structured. The density of trichomes was the highest in the bud and tender leaf periods. Further, using the high-throughput sequencing method, we identified 48,856 unigenes, of which 31,574 were differentially expressed. In an analysis of 208 differentially expressed genes (DEGs) encoding transcription factors (TFs), five may involve in trichome development. In addition, on the basis of the Gene Ontology (GO) annotation and the weighted gene co-expression network analysis (WGCNA) results, we screened several DEGs that may contribute to trichome growth, including 66 DEGs related to plant resistance genes (PRGs), 172 DEGs related to cell wall biosynthesis pathway, 29 DEGs related to cell cycle pathway, and 45 DEGs related to cytoskeleton biosynthesis. Collectively, this study provided high-quality RNA-seq information to improve our understanding of the molecular regulatory mechanism of trichome development and lay a foundation for additional trichome studies in tea plants.

Comparative Transcriptome Analysis of Agrobacterium tumefaciens Reveals the Molecular Basis for the Recalcitrant Genetic Transformation of Camellia sinensis L.

Tea (Camellia sinensis L.), an important economic crop, is recalcitrant to Agrobacterium-mediated transformation (AMT), which has seriously hindered the progress of molecular research on this species. The mechanisms leading to low efficiency of AMT in tea plants, related to the morphology, growth, and gene expression of Agrobacterium tumefaciens during tea-leaf explant infection, were compared to AMT of Nicotiana benthamiana leaves in the present work. Scanning electron microscopy (SEM) images showed that tea leaves induced significant morphological aberrations on bacterial cells and affected pathogen-plant attachment, the initial step of a successful AMT. RNA sequencing and transcriptomic analysis on Agrobacterium at 0, 3 and 4 days after leaf post-inoculation resulted in 762, 1923 and 1656 differentially expressed genes (DEGs) between the tea group and the tobacco group, respectively. The expressions of genes involved in bacterial fundamental metabolic processes, ATP-binding cassette (ABC) transporters, two-component systems (TCSs), secretion systems, and quorum sensing (QS) systems were severely affected in response to the tea-leaf phylloplane. Collectively, these results suggest that compounds in tea leaves, especially gamma-aminobutyrate (GABA) and catechins, interfered with plant-pathogen attachment, essential minerals (iron and potassium) acquisition, and quorum quenching (QQ) induction, which may have been major contributing factors to hinder AMT efficiency of the tea plant.

Development and Application of a Fast Gas Chromatographic Method Offer New Insights into l-theanine Production Regulation in Camellia sinensis L.

Tea is the most consumed beverage worldwide, and l-theanine in tea leaves significantly affects their flavor and market quality. We have developed and validated a fast and reliable gas chromatographic method with flame ionization detection (GC-FID) to quantify l-theanine after its extraction from Camellia sinensis (tea plant) and derivatization. The procedure was completed in 40 min, from extraction to chromatographic analysis, with a recovery rate of more than 93% and allowing a high sample throughput. The GC-FID intraday precision was within 0.57-2.28%, while the interday precision ranged from 1.57 to 13.48%. The intraday accuracy ranged from -6.84 to 5.26%, while the interday accuracy ranged from -1.08 to 3.12%. The limit of detection was 2.28 µg/mL, and the limit of quantification was 6.47 µg/mL. The GC-FID method was validated by high-performance liquid chromatography with UV detection (HPLC-UV) and was used to investigate the biosynthesis and regulation of l-theanine in tea plants. We found that plants fed with ethylamine significantly increased l-theanine concentrations in roots, while exogenous supplementation of glutamic acid, carbamide, and glutamine did not significantly affect the l-theanine level in roots. Our results also indicated that roots were not indispensable for the biosynthesis of l-theanine, which was detected in undifferentiated embryonic calluses in concentrations (g/100 g dry weight) as high as in leaves of whole plants (1.67 and 1.57%, respectively) and without any exogenous theanine precursor supplementation.