Genetics and breeding of phenolic content in tomato, eggplant and pepper fruits

A R2R3-MYB transcription factor LmMYB111 positively regulates chlorogenic acid and luteoloside biosynthesis in Lonicera macranthoides

Lonicera macranthoides is a vital medicinal herb frequently used in Chinese traditional medicine. Chlorogenic acid (CGA) and luteoloside are the most crucial bioactive pharmaceutical ingredients in L. macranthoides. Although CGA and luteoloside biosynthetic pathway and structural genes appeared to be extensively elucidated, the transcriptional regulation has yet to be unveiled. Here, integration of transcriptome and metabolome revealed a R2R3-MYB transcription factor LmMYB111 positively correlated with CGA concentration, which shares close homology with AtMYB111 and acts as a transcriptional activator. Overexpressing LmMYB111 in tobacco and Lonicera resulted in enhanced production of CGA and luteoloside. RNA-Seq demonstrated that overexpression of LmMYB111 dramatically upregulated CGA and luteoloside biosynthetic genes, including 10 PALs, 3 C4Hs, 7 4CLs, 4 HCT/HQTs, 3 CHSs and 5 CHIs. DNA Affinity Purification sequencing (DAP-Seq) revealed the binding motifs of LmMYB111 and 1135 downstream targets, including structural genes e.g. PAL1/PAL4s, C4H, 4CL2, CHI, and DFR as well as several transcription factors (TFs), e.g. MYB3/MYB4, bHLH62/TT8, BEL1, SCL15/SCL32 and ERF3.The electrophoretic mobility shift assay (EMSA) together with dual-luciferase reporter system (DLR) further proved that LmMYB111 bound to and activated proLmMYB4, proLmPAL1, proLm4CL2, proLmCHI and proLmDFR, therefore facilitating hyperaccumulation of CGA, luteoloside and other phenolics. These findings shed light on the participation of LmMYB111 in CGA and luteoloside biosynthetic regulatory networks in L. macranthoides mediated by controlling the expression of structural genes and TFs, which will contribute to elevate phenolics production by genetic engineering.

Functional Characterization of Grapevine VviMYC4 in Regulating Drought Tolerance by Mediating Flavonol Biosynthesis

Drought ranks among the key abiotic stresses that limit the growth and yield of grapevines (Vitis vinifera L.). Flavonols, a class of antioxidants commonly found in grapevines, play a crucial role in combating drought stress. In this study, we characterized the function and regulatory mechanism of the grapevine VviMYC4 in mediating flavonol biosynthesis in response to drought stress. VviMYC4 encodes a protein of 468 amino acids with conserved bHLH-MYC_N and bHLH domains. Phylogenetic analysis confirmed its homology with the grapevine VviMYC2 and similarity in function. The expression of VviMYC4 in 'Cabernet Sauvignon' grapevine seedling leaves increased initially and then decreased during prolonged drought stress. The homologous and heterologous transformation of VviMYC4 in grape suspension cells, Arabidopsis plants, tobacco leaves, and grapevine leaves demonstrated its ability to positively regulate flavonol biosynthesis and accumulation by promoting the expression of flavonol-related genes, thereby enhancing the drought tolerance of transgenic plants. Furthermore, VviMYC4 could bind to specific E-box sites on the promoters of VviF3H and VviFLS to improve their activities. This study highlights VviMYC4 as a pivotal positive regulator of drought tolerance in grapevines and proposes that VviMYC4 enhances the antioxidant and reactive oxygen species (ROS) scavenging abilities of grapevines in challenging environments and improves their stress resilience by mediating flavonol biosynthesis. Our findings offer crucial candidate genes and valuable insights for the molecular breeding of grapevine drought resistance.

Nitrogen cycle induced by plant growth-promoting rhizobacteria drives "microbial partners" to enhance cadmium phytoremediation

BACKGROUND

Using plant growth-promoting rhizobacteria (PGPR) combined with hyperaccumulator is an ecologically viable way to remediate cadmium (Cd) pollution in agricultural soil. Despite recent advances in elucidating PGPR-enhanced phytoremediation, the response of plant-associated microbiota to PGPR remains unclear.

RESULTS

Here, we found that the effective colonization of PGPR reshaped the rhizosphere nutrient microenvironment, especially driving the nitrogen cycle, primarily mediated by soil nitrate reductase (S-NR). Elevated S-NR activity mobilized amino acid metabolism and synthesis pathways in the rhizosphere, subsequently driving a shift in life history strategies of the rhizosphere microbiota, and enriching specific rare taxa. The reconstructed synthetic community (SynCom3) confirmed that the inclusion of two crucial collaborators (Lysobacter and Microbacterium) could efficiently foster the colonization of PGPR and aid PGPR in executing phytoremediation enhancement. Finally, the multi-omics analysis highlighted the critical roles of phenylpropanoid biosynthesis and tryptophan metabolism pathways in inducing SynCom3 reorganization and PGPR-enhanced phytoremediation.

CONCLUSIONS

Our results underscore the significance of the rhizosphere microenvironment modification by PGPR for its colonization and efficacy, and highlight the collaborative role of rare microbiota in the context of PGPR-enhanced phytoremediation. Video Abstract.

The effects of post-harvest pretreatments and drying methods on in vitro bioaccessibility of phenolics and carotenoids in tomato (Solanum lycopersicum) cultivars

Two pretreatments (ultrasound sonication [US] and microwave [MW]) and drying techniques (hot air [HA] and freeze-drying [FD]) were used to assess the in vitro bioaccessibility of phenols, carotenoids, and antioxidant activity in three tomato cultivars (Zzx171, Zzx162, and Zzx65). The metabolome-chemometric analysis showed that tomato cultivars dried by FD and HA differed in metabolites. HA samples contained methoxytyrosine and aconitane-type diterpenoids. US-HA enhanced total phenol content bioaccessibility by 64.72%-74.25% in three tomato cultivars after digestion (intestinal phase). US-HA increased the protocatechuic acid levels in all three tomato cultivars in the intestinal phase, but by 55.23% in Zzx65 compared to the undigested samples. Despite all adopted postharvest pretreatments and drying, US-HA retained chlorogenic acid, 4-O-caffeinyliquinic acid, and rutin better, due to microstructure changes in the intestinal phase, and Zzx65 treated with US-HA retained the most. In undigested samples, US-FD improved total carotenoids, lycopene, and β-carotene retention, but the inaccessibility was reduced significantly during in vitro digestion. Cultivar × postharvest treatment affected all phenolic compounds, carotenoids, and antioxidant activities in the intestinal phase. US-HA had improved antioxidant power (FRAP) and 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) scavenging activity in the intestinal phase. PRACTICAL APPLICATION: Tomatoes are an important part of the human diet. Their high perishability reduces their nutritional and microbiological quality. The lack of cold storage infrastructure in developing countries contributes to food waste. Convective hot air drying is suitable for recycling fresh market waste products as supplement powders. The ultrasound pretreatment protects bioactive compounds in tomato fruit and is non-thermal. There are several limitations, including equipment cost, energy efficiency, and integration with commercial systems, which limit ultrasound-assisted drying's scalability. The integration of US-HA treatment (ultrasound-assisted hot air drying) could reduce food waste and contribute to the sustainable development goals in agricultural industries.

Identification of tomato F-box proteins functioning in phenylpropanoid metabolism

Phenylpropanoids, a class of specialized metabolites, play crucial roles in plant growth and stress adaptation and include diverse phenolic compounds such as flavonoids. Phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) are essential enzymes functioning at the entry points of general phenylpropanoid biosynthesis and flavonoid biosynthesis, respectively. In Arabidopsis, PAL and CHS are turned over through ubiquitination-dependent proteasomal degradation. Specific kelch domain-containing F-Box (KFB) proteins as components of ubiquitin E3 ligase directly interact with PAL or CHS, leading to polyubiquitinated PAL and CHS, which in turn influences phenylpropanoid and flavonoid production. Although phenylpropanoids are vital for tomato nutritional value and stress responses, the post-translational regulation of PAL and CHS in tomato remains unknown. We identified 31 putative KFB-encoding genes in the tomato genome. Our homology analysis and phylogenetic study predicted four PAL-interacting SlKFBs, while SlKFB18 was identified as the sole candidate for the CHS-interacting KFB. Consistent with their homolog function, the predicted four PAL-interacting SlKFBs function in PAL degradation. Surprisingly, SlKFB18 did not interact with tomato CHS and the overexpression or knocking out of SlKFB18 did not affect phenylpropanoid contents in tomato transgenic lines, suggesting its irreverence with flavonoid metabolism. Our study successfully discovered the post-translational regulatory machinery of PALs in tomato while highlighting the limitation of relying solely on a homology-based approach to predict interacting partners of F-box proteins.

Foliar application protected vegetable against poisonous element cadmium and mitigated human health risks

Foliar application has been reported as an effective method to facilitate plant growth and mitigate cadmium (Cd) accumulation. However, the application of foliar fertilizers on plant production, Cd uptake and health risks of Solanaceae family remains unknown. In this study, four foliar fertilizers were applied to investigate their effects on the production, Cd accumulation and human health risk assessment of two varieties of pepper (Capsicum annuum L.) and eggplant (Solanum melongena L.), respectively. Compared with CK, the foliar application increased vegetable production to 104.16 %-123.70 % in peppers, and 100.83 %-105.17 % in eggplants, accordingly. The application of foliar fertilizers largely decreased Cd TF (transportation factor) by up to 23.32 % in JY, 18.37 % in GJ of pepper varieties, and up to 14.47 % in ZL, 15.24 % in HGR of eggplant varieties. Moreover, Cd BAF (bioaccumulation factor) also declined to different extents after the application of foliar fertilizers. As for human health risk assessments, foliar application diminished the hazard index (HI) and carcinogenic risk (CR) of both pepper and eggplant varieties. The results concluded that the application of composed foliar fertilizers was most effective, and could be a promising alternative for the improvement of vegetable production and mitigation of vegetable Cd accumulation and human health risks as well. The results further highlighted the understanding of foliar fertilizer application on vegetable production and health risks, which benefited better vegetable safe production and further guaranteed human health.

Characterization of Browning, Chlorogenic Acid Content, and Polyphenol Oxidase Activity in Different Varietal Types of Eggplant (Solanum melongena) for Improving Visual and Nutritional Quality

Eggplant (Solanum melongena L.) breeding for fruit quality has mostly focused on visual traits and nutritional and bioactive compounds, including chlorogenic acid. However, higher contents of chlorogenic acid may lead to more pronounced fruit flesh browning. We examined a diverse collection of 59 eggplant accessions across five varietal types ('black oval', 'striped', 'anthocyanin-free', 'purple', and 'black elongated') to evaluate the degree of browning, polyphenol oxidase (PPO) activity, and chlorogenic acid (CGA) content. The results reveal moderate correlations among these traits, with no clear differences among the varietal types, suggesting that other factors, including genetic variation, might significantly influence these traits. Notably, 'black oval' accessions demonstrated higher browning and PPO activity, whereas 'striped' accessions showed low variability. The identification of genotypes with lower browning and higher CGA content highlights opportunities for targeted genotype selection to improve eggplant chlorogenic acid content while maintaining low or moderate browning, pointing towards the importance of genetic considerations in breeding strategies to reduce browning and enhance nutritional value.

Food phenolics and Lactiplantibacillus plantarum

Phenolic compounds are important constituents of plant food products. These compounds play a key role in food characteristics such as flavor, astringency and color. Lactic acid bacteria are naturally found in raw vegetables, being Lactiplantibacillus plantarum the most commonly used commercial starter for the fermentation of plant foods. Hence, the metabolism of phenolic compounds of L. plantarum has been a subject of study in recent decades. Such studies confirm that L. plantarum, in addition to presenting catalytic capacity to transform aromatic alcohols and phenolic glycosides, exhibits two main differentiated metabolic routes that allow the biotransformation of dietary hydroxybenzoic and hydroxycinnamic acid-derived compounds. These metabolic pathways lead to the production of new compounds with new biological and organoleptic properties. The described metabolic pathways involve the action of specialized esterases, decarboxylases and reductases that have been identified through genetic analysis and biochemically characterized. The purpose of this review is to provide a comprehensive and up-to-date summary of the current knowledge of the metabolism of food phenolics in L. plantarum.

The challenge of breeding for reduced off-flavor in faba bean ingredients

The growing interest in plant protein sources, such as pulses, is driven by the necessity for sustainable food production and climate change mitigation strategies. Faba bean (Vicia faba L.) is a promising protein crop for temperate climates, owing to its remarkable yield potential (up to 8 tonnes ha-1 in favourable growing conditions) and high protein content (~29% dry matter basis). Nevertheless, the adoption of faba bean protein in plant-based products that aim to resemble animal-derived counterparts is hindered by its distinctive taste and aroma, regarded as "off-flavors". In this review, we propose to introduce off-flavor as a trait in breeding programs by identifying molecules involved in sensory perception and defining key breeding targets. We discuss the role of lipid oxidation in producing volatile and non-volatile compounds responsible for the beany aroma and bitter taste, respectively. We further investigate the contribution of saponin, tannin, and other polyphenols to bitterness and astringency. To develop faba bean varieties with diminished off-flavors, we suggest targeting genes to reduce lipid oxidation, such as lipoxygenases (lox) and fatty acid desaturases (fad), and genes involved in phenylpropanoid and saponin biosynthesis, such as zero-tannin (zt), chalcone isomerase (chi), chalcone synthase (chs), β-amyrin (bas1). Additionally, we address potential challenges, including the need for high-throughput phenotyping and possible limitations that could arise during the genetic improvement process. The breeding approach can facilitate the use of faba bean protein in plant-based food such as meat and dairy analogues more extensively, fostering a transition toward more sustainable and climate-resilient diets.

Antioxidant and Anti-Diabetic Properties of Olive (Olea europaea) Leaf Extracts: In Vitro and In Vivo Evaluation

(1) Objective: The main objective of the current study was to evaluate in vitro and in vivo an antioxidant property of three genotypes of olive leaf extract (OLE) (picual, tofahi and shemlali), and furthermore to assess potential activity in the treatment and/or prevention of diabetes mellitus type II and related implications. (2) Methodology: Antioxidant activity was determined by using three different methods (DDPH assay, reducing power and nitric acid scavenging activity). In vitro α-glucosidase inhibitory activity and hemolytic protective activity were assessed for the OLE. Five groups of male rats were used in in vivo experiment for evaluating the antidiabetic potential of OLE. (3) Results: The genotypes of the extracts of the three olive leaves exhibited meaningful phenolic and flavonoids content with superiority for picual extract (114.79 ± 4.19 µg GAE/g and 58.69 ± 1.03 µg CE/g, respectively). All three genotypes of olive leaves demonstrated significant antioxidant activity when using DPPH, reducing power and nitric oxide scavenging activity with IC50 ranging from 55.82 ± 0.13 to 19.03 ± 0.13 μg/mL. OLE showed a significant α-glucosidase inhibition activity and dose-dependent protection from hemolysis. In vivo experimentation revealed that the administration of OLE alone and the combination of OLE+ metformin clearly restored the blood glucose and glycated hemoglobin, lipid parameters and liver enzymes to the normal level. The histological examination revealed that the OLE and its combination with metformin successfully repaired the liver, kidneys and pancreatic tissues to bring them close to the normal status and maintain their functionality. (4) Conclusion: Finally, it can be concluded that the OLE and its combination with metformin is a promising treatment for diabetes mellitus type 2 due to their antioxidant activity, which emphasizes the potential use of OLE alone or as an adjuvant agent in the treatment protocol of diabetes mellitus type II.