Background: The basic helix–loop–helix (bHLH) transcription factors (TFs) serve crucial roles in regulating plant growth and development and typically participate in biological processes by interacting with other TFs. Capsorubin and capsaicinoids are found only in Capsicum, which has high nutritional and economic value. However, whether bHLH family genes regulate capsorubin and capsaicinoid biosynthesis and participate in these processes by interacting with other TFs remains unknown. Results: In this study, a total of 107 CabHLHs were identified from the Capsicum annuum genome. Phylogenetic tree analysis revealed that these CabHLH proteins were classified into 15 groups by comparing the CabHLH proteins with Arabidopsis thaliana bHLH proteins. The analysis showed that the expression profiles of CabHLH009, CabHLH032, CabHLH048, CabHLH095 and CabHLH100 found in clusters C1, C2, and C3 were similar to the profile of carotenoid biosynthesis in pericarp, including zeaxanthin, lutein and capsorubin, whereas the expression profiles of CabHLH007, CabHLH009, CabHLH026, CabHLH063 and CabHLH086 found in clusters L5, L6 and L9 were consistent with the profile of capsaicinoid accumulation in the placenta. Moreover, CabHLH007, CabHLH009, CabHLH026 and CabHLH086 also might be involved in temperature-mediated capsaicinoid biosynthesis. Yeast two-hybrid (Y2H) assays demonstrated that CabHLH007, CabHLH009, CabHLH026, CabHLH063 and CabHLH086 could interact with MYB31, a master regulator of capsaicinoid biosynthesis. Conclusions: The comprehensive and systematic analysis of CabHLH TFs provides useful information that contributes to further investigation of CabHLHs in carotenoid and capsaicinoid biosynthesis.

Potassium is among the three essential macronutrients for tea plants, along with nitrogen and phosphorous, and plays important roles in growth and stress response. Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium. At present, more than 59% of China’s tea gardens are in a state of potassium deficiency, which negatively affects tea quality and yield. This paper reviews the effects of potassium deficiency on tea plant growth and stress response, details factors affecting potassium supply and demand in tea gardens, examines the interactions between potassium and other elements in soils, and provides strategies for optimizing potassium levels in soils. Potassium is positively correlated with the elements nitrogen, copper, and zinc. Sufficient potassium dramatically improves the yield and quality of tea: it accelerates metabolism, promotes synthesis of catechins, and strengthens biotic and abiotic resistance by activating and regulating different enzymes. Moderate application of potassium fertilizers, along with potassium-solubilizing bacteria, can regulate the ratio of different forms of potassium and increase available potassium in soils of tea gardens. We suggest that research on potassium occurring in soils and its interaction with other elements be strengthened, so as to improve the efficient use of potassium fertilizers in tea gardens and maintain the balance of elements in soils.

Our study investigated the impact of nitrogen fertilization at 0, 150, 300, and 450 kg/ha on the non-volatile and volatile substances, as well as gene expression in fresh leaves from Lingtou tea plants. We found that applying nitrogen at 450 kg/ha notably increased total polyphenols (TPs) and free amino acids (AAs) while decreasing the TP to AA ratio (TP/AA) and total catechins (TC) contents. Chlorophyll, caffeine (CAF) and theanine accumulated to a greater extent with nitrogen application rates of 150, 300, and 450 kg/ha, respectively, six substances – TP, CAF, TC, theanine, epigallocatechin (EGC), and AA – as key contributors to the taste quality of LTDC. Additionally, five substances with variable importance in projections (VIP) ≥ 1 and odor activation values (OAV) ≥ 1, notably linalool and cis-linalool oxide (furanoid), significantly contributed to the tea's overall aroma. Furthermore, applying 300 kg/ha nitrogen upregulated the dihydroflavonol reductase (DFR)gene, likely causing catechin decrease.

The plateaus of Tibet have a unique climate that poses a great challenge for local agriculture. To promote sustainable development in Tibet, an elite tea variety has been introduced. However, the modifications of tea flavors in response to the climate of the plateaus are unknown. In this study, volatile organic compounds (VOCs) and other taste substances of tea planted in its original location (OOT) and in Tibet (TOT) were systematically analyzed and compared. The volatile components in TOT and OOT showed a slight difference, and principal component analysis revealed that the characteristic aroma compounds distinguishing tea grown in Tibet from tea grown in Guangdong were hotrienol and benzyl alcohol. In terms of taste substances, TOT exhibited higher levels of water extractable compounds, including polyphenols and amino acids, but lower levels of caffeine than OOT, which implies that TOT may taste better than OOT. To our knowledge, this is the first study to describe the changes in aroma and flavor profiles of tea induced by high altitude systematically, which will provide a basis for reference during the introduction and cultivation of tea crops to the plateaus of Tibet.

Proper postharvest storage preserves horticultural products, including tea, until they can be processed. However, few studies have focused on the physiology of ripening and senescence during postharvest storage, which affects the flavor and quality of tea. In this study, physiological and biochemical indexes of the leaves of tea cultivar ‘Yinghong 9′ preserved at a low temperature and high relative humidity (15–18 °C and 85–95%, PTL) were compared to those of leaves stored at ambient conditions (24 ± 2 °C and relative humidity of 65% ± 5%, UTL). Water content, chromatism, chlorophyll fluorescence, and key metabolites (caffeine, theanine, and catechins) were analyzed over a period of 24 h, and volatilized compounds were determined after 24 h. In addition, the expression of key biosynthesis genes for catechin, caffeine, theanine, and terpene were quantified. The results showed that water content, chromatism, and chlorophyll fluorescence of preserved leaves were more similar to fresh tea leaves than unpreserved tea leaves. After 24 h, the content of aroma volatiles and caffeine significantly increased, while theanine decreased in both groups. Multiple catechin monomers showed distinct changes within 24 h, and EGCG was significantly higher in preserved tea. The expression levels of CsFAS and CsTSI were consistent with the content of farnesene and theanine, respectively, but TCS1 and TCS2 expression did not correlate with caffeine content. Principal component analysis considered results from multiple indexes and suggested that the freshness of PTL was superior to that of UTL. Taken together, preservation conditions in postharvest storage caused a series of physiological and metabolic variations of tea leaves, which were different from those of unpreserved tea leaves. Comprehensive evaluation showed that the preservation conditions used in this study were effective at maintaining the freshness of tea leaves for 2–6 h. This study illustrates the metabolic changes that occur in postharvest tea leaves, which will provide a foundation for improvements to postharvest practices for tea leaves.