Light Intensity Modulates the Effect of Phosphate Limitation on Carbohydrates, Amino Acids, and Catechins in Tea Plants (Camellia sinensis L.)

Transcriptome and metabolome analysis reveals mechanism of light intensity modulating iridoid biosynthesis in Gentiana macrophylla Pall

Light intensity is a key factor affecting the synthesis of secondary metabolites in plants. However, the response mechanisms of metabolites and genes in Gentiana macrophylla under different light intensities have not been determined. In the present study, G. macrophylla seedlings were treated with LED light intensities of 15 µmol/m2/s (low light, LL), 90 µmol/m2/s (medium light, ML), and 200 µmol/m2/s (high light, HL), and leaves were collected on the 5th day for further investigation. A total of 2162 metabolites were detected, in which, the most abundant metabolites were identified as flavonoids, carbohydrates, terpenoids and amino acids. A total of 3313 and 613 differentially expressed genes (DEGs) were identified in the LL and HL groups compared with the ML group, respectively, mainly enriched in KEGG pathways such as carotenoid biosynthesis, carbon metabolism, glycolysis/gluconeogenesis, amino acids biosynthesis, plant MAPK pathway and plant hormone signaling. Besides, the transcription factors of GmMYB5 and GmbHLH20 were determined to be significantly correlated with loganic acid biosynthesis; the expression of photosystem-related enzyme genes was altered under different light intensities, regulating the expression of enzyme genes involved in the carotenoid, chlorophyll, glycolysis and amino acids pathway, then affecting their metabolic biosynthesis. As a result, low light inhibited photosynthesis, delayed glycolysis, thus, increased certain amino acids and decreased loganic acid production, while high light got an opposite trend. Our research contributed significantly to understand the molecular mechanism of light intensity in controlling metabolic accumulation in G. macrophylla.

CsEXL3 regulate mechanical harvest-related droopy leaves under the transcriptional activation of CsBES1.2 in tea plant

Due to a labor shortage, the mechanical harvesting of tea plantations has become a focal point. However, mechanical harvest efficiency was hampered by droopy leaves, leading to a high rate of broken tea shoots and leaves. Here, we dissected the genetic structure of leaf droopiness in tea plants using genome-wide association studies (GWAS) on 146 accessions, combined with transcriptome from two accessions with contrasting droopy leaf phenotypes. A set of 16 quantitative trait loci (QTLs) containing 54 SNPs and 34 corresponding candidate genes associated with droopiness were then identified. Among these, CsEXL3 (EXORDIUM-LIKE 3) from Chromosome 1 emerged as a candidate gene. Further investigations revealed that silencing CsEXL3 in tea plants resulted in weaker vascular cell malformation and brassinosteroid-induced leaf droopiness. Additionally, brassinosteroid signal factor CsBES1.2 was proved to participate in CsEXL3-induced droopiness and vascular cell malformation via using the CsBES1.2-silencing tea plant. Notably, CsBES1.2 bound on the E-box of CsEXL3 promoter to transcriptionally activate CsEXL3 expression as CUT&TAG based ChIP-qPCR and ChIP-seq suggested in vivo as well as EMSA and Y1H indicated in vitro. Furthermore, CsEXL3 instead of CsBES1.2 decreased lignin content and the expressing levels of lignin biosynthesis genes. Overall, our findings suggest that CsEXL3 regulates droopy leaves, partially through the transcriptional activation of CsBES1.2, with the potential to improve mechanical harvest efficiency in tea plantations.

Depicting the genetic and metabolic panorama of chemical diversity in the tea plant

As a frequently consumed beverage worldwide, tea is rich in naturally important bioactive metabolites. Combining genetic, metabolomic and biochemical methodologies, here, we present a comprehensive study to dissect the chemical diversity in tea plant. A total of 2837 metabolites were identified at high-resolution with 1098 of them being structurally annotated and 63 of them were structurally identified. Metabolite-based genome-wide association mapping identified 6199 and 7823 metabolic quantitative trait loci (mQTL) for 971 and 1254 compounds in young leaves (YL) and the third leaves (TL), respectively. The major mQTL (i.e., P < 1.05 × 10-5, and phenotypic variation explained (PVE) > 25%) were further interrogated. Through extensive annotation of the tea metabolome as well as network-based analysis, this study broadens the understanding of tea metabolism and lays a solid foundation for revealing the natural variations in the chemical composition of the tea plant. Interestingly, we found that galloylations, rather than hydroxylations or glycosylations, were the largest class of conversions within the tea metabolome. The prevalence of galloylations in tea is unusual, as hydroxylations and glycosylations are typically the most prominent conversions of plant specialized metabolism. The biosynthetic pathway of flavonoids, which are one of the most featured metabolites in tea plant, was further refined with the identified metabolites. And we demonstrated the further mining and interpretation of our GWAS results by verifying two identified mQTL (including functional candidate genes CsUGTa, CsUGTb, and CsCCoAOMT) and completing the flavonoid biosynthetic pathway of the tea plant.

Metabolic footprints in phosphate-starved plants

Plants' requirement of Phosphorus (P) as an essential macronutrient is obligatory for their normal growth and metabolism. Besides restricting plants' primary growth, P depletion affects both primary and secondary metabolism and leads to altered levels of sugars, metabolites, amino acids, and other secondary compounds. Such metabolic shifts help plants optimize their metabolism and growth under P limited conditions. Under P deprivation, both sugar levels and their mobilization change that influences the expression of Pi starvation-inducible genes. Increased sugar repartitioning from shoot to root help root growth and organic acids secretion that in turn promotes phosphate (Pi) uptake from the soil. Other metabolic changes such as lipid remodeling or P reallocation from older to younger leaves release the P from its bound forms in the cell. In this review, we summarize the metabolic footprinting of Pi-starved plants with respect to the benefits offered by such metabolic changes to intracellular Pi homeostasis.

Assessment of CuO NPs on soil microbial community structure based on phospholipid fatty acid techniques and phytotoxicity of bok choy seedlings

In this study, a soil culture and a hydroponic experiment were conducted to assess the toxicology effects of copper oxide nanoparticles (CuO NPs) on soil microbial community structure and the growth of bok choy. Results showed CuO NPs had an inhibitory effect on soil microbial abundance, diversity, and activity, as well as the bok choy seedling growth, whereas CuO NPs at low concentrations did not significantly affect the soil microbial biomass or plant growth. In soil, CuO NPs at high dose (80 mg kg^-1) significantly reduced the indexes of Simpson diversity, Shannon-Wiener diversity and Pielou evenness by 3.7%, 4.9% and 4.5%, respectively. In addition, CuO NPs at 20 and 80 mg kg^-1 treatment significantly reduced soil enzymes (urease, alkaline phosphatase, dehydrogenase, and catalase) activities by 25.5%-58.9%. Further, CuO NPs at 20 mg L^-1 significantly inhibited the growth of plant root by 33.8%, and catalase (CAT) activity by 17.9% in bok choy seedlings. The present study can provide a basis for a comprehensive evaluation of the toxicity effect of CuO NPs on soil microorganisms and phytotoxicity to bok choy seedlings.

Effect of Interactions between Phosphorus and Light Intensity on Metabolite Compositions in Tea Cultivar Longjing43

Light intensity influences energy production by increasing photosynthetic carbon, while phosphorus plays an important role in forming the complex nucleic acid structure for the regulation of protein synthesis. These two factors contribute to gene expression, metabolism, and plant growth regulation. In particular, shading is an effective agronomic practice and is widely used to improve the quality of green tea. Genotypic differences between tea cultivars have been observed as a metabolic response to phosphorus deficiency. However, little is known about how the phosphorus supply mediates the effect of shading on metabolites and how plant cultivar gene expression affects green tea quality. We elucidated the responses of the green tea cultivar Longjing43 under three light intensity levels and two levels of phosphorus supply based on a metabolomic analysis by GC×GC-TOF/MS (Two-dimensional Gas Chromatography coupled to Time-of-Flight Mass Spectrometry) and UPLC-Q-TOF/MS (Ultra-Performance Liquid Chromatography-Quadrupole-Time of Flight Mass Spectrometry), a targeted analysis by HPLC (High Performance Liquid Chromatography), and a gene expression analysis by qRT-PCR. In young shoots, the phosphorus concentration increased in line with the phosphate supply, and elevated light intensities were positively correlated with catechins, especially with epigallocatechin of Longjing43. Moreover, when the phosphorus concentration was sufficient, total amino acids in young shoots were enhanced by moderate shading which did not occur under phosphorus deprivation. By metabolomic analysis, phenylalanine, tyrosine, and tryptophan biosynthesis (PTT) were enriched due to light and phosphorus effects. Under shaded conditions, SPX2 (Pi transport, stress, sensing, and signaling), SWEET3 (bidirectional sugar transporter), AAP (amino acid permeases), and GSTb (glutathione S-transferase b) shared the same analogous correlations with primary and secondary metabolite pathways. Taken together, phosphorus status is a crucial factor when shading is applied to increase green tea quality.