Lettuce is a critical leafy vegetable consumed worldwide and is a substantial dietary source of health-promoting compounds. Exploring changes in metabolism during lettuce domestication under artificial selection conditions is important to facilitate further breeding and cultivation for quality improvement. A liquid chromatography-mass spectrometry-based metabolomics approach was used to putatively identify 237 metabolites from 40 accessions, of which 130 were identified as metabolite identification level 1. Subsequently, 29 metabolites linked to lettuce quality improvement and their potential associated genes involved in lettuce domestication and differentiation were analysed. Muti-omics approach showed that metabolites involved in flavonol biosynthesis are the main metabolic distinctions between wild and modern cultivars, which is attributable to the selection signal observed in LsF3 ' H, a key enzyme involved in the catalysis of flavonoid hydroxylation at the 3 '-position. These findings provide a comprehensive view of quality- and flavour-related metabolite variation in lettuce, reveal the potential for quality improvement associated with flavonol biosynthesis, and offer valuable insights into the genetic basis for improving lettuce flavour and nutrition.

To elucidate how roots respond to hydroponics, we investigated the mechanisms by which nutrient solution flow influences root growth in hydroponic lettuce via phenotypic analysis combined with single-cell RNA sequencing. Nutrient solution flow exerted a dual-phase effect on lettuce root growth, characterized by initial inhibition followed by subsequent promotion. Although initially, root biomass and morphological indices were significantly lower under flow treatment than under static treatment, this trend rapidly reversed by days 2 and 3 and all the measured indices showed improved root growth under flow treatment. Single-cell transcriptomic analysis enabled the construction of a comprehensive cellular atlas of hydroponic lettuce roots, which indicated heterogeneous transcriptional responses for lettuce roots under static and flow treatments. Flow treatment altered root cell composition, inducing decreases in initial cells and increases in vascular cells. Pseudotime trajectory analysis suggested that the differentiation of initial cells into vascular tissues was associated with plant hormone signaling and MAPK pathway-related gene expression, and also revealed differential expression of key functional genes, including ACO3 in root cap cells and CAM7 in xylem cells. Therefore, this study provides insights into the transcriptional regulatory framework of hydroponic lettuce roots in response to nutrient solution flow, which may provide a basis for optimizing hydroponic crop production via rhizosphere environment regulation.

Soilless culture enables precise control of root-zone environments, offering solutions to land scarcity and food security. Plant roots exhibit high phenotypic plasticity, yet no recent review has systematically synthesized how biotic and abiotic factors jointly shape root morphology and physiology specifically under soilless conditions. This review synthesizes literature from the past two decades, focusing on studies that examine root responses in hydroponic, aeroponic, and substrate-based soilless systems. We organize the evidence into three parts: (1) biotic factors (plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and pathogens); (2) abiotic factors (light intensity/spectrum, temperature, rhizosphere oxygen, and nutrient solution properties including concentration, composition, pH, and flow rate); and (3) interactive effects between these factors. Our analysis reveals three main insights. First, in soilless systems, the simplified microbial environment amplifies both the beneficial effects of PGPR/AMF (via phytohormone modulation and antioxidant activation) and the virulence of pathogens, compared to soil conditions. Second, among abiotic factors, light quality and nutrient solution flow have emerged as particularly potent regulators—blue/red light differentially control auxin transport, while flow-induced mechanical force alters lignin deposition and hormone signaling in ways not observed in static soil. Third, emerging evidence indicates that biotic–abiotic interactions (e.g., microbes × pH, light × temperature, oxygen × nutrient composition) produce non-additive effects on root architecture that single-factor studies cannot predict. We identify five critical gaps: insufficient multi-factor coupling studies, limited molecular understanding of root response networks under combined stresses, lack of crop-specific regulation models, a triple bottleneck in PGPR strain–environment–host adaptation, and high energy/material costs of soilless systems. Future priorities should integrate multi-omics with AI-driven environmental control and CRISPR-based root trait engineering. This review provides a framework for understanding root-environment interactions in soilless culture and outlines a research base for precision root-zone management.

The amino acid transporter (AAT) gene family encodes a group of membrane proteins in plants that mediate amino acid transport, regulate nitrogen allocation, and contribute to stress adaptation. In this study, a total of 102 LsAATs were identified in lettuce. They were classified into 12 subfamilies and distributed across all the chromosomes. Forty percent of them were expanded via gene duplication, and 23 and 18 LsAATs were segmentally and tandemly duplicated, respectively. Considerable variations in physicochemical properties, conserved motifs, and cis-acting elements were observed among these genes. The LsAATs and phenolic compounds regulated by continuous lighting and light quality were analyzed. Furthermore, three-dimensional structural models of light-regulated LsAATs were constructed and subsequently aligned with characterized homologs in other species. The results suggested that several light-regulated LsAATs might be involved in quality changes, nutrient uptake, long-distance transport, and stress adaptation. Overall, LsAATs are evolutionarily stable in plants and diverse in terms of their physicochemical properties and potential molecular biology.

Plant factories (PFs), also known as vertical farms, are advanced agricultural production systems that operate independently of geographical and environmental conditions. They utilize artificial light and controlled environments to produce horticultural plants year-round. This approach offers a promising solution for the stable and efficient supply of high-quality horticultural produce in urban areas, enhancing resilient urban food systems. This review explores the economic and environmental impacts and potential of PFs. Breakthroughs in PF research and development are highlighted, including increased product yields and quality, reduced energy input and CO2 emissions through optimized growing conditions and automation systems, transitioning to clean energy, improved resource use efficiency, and reduced food transport distances. Moreover, innovations and applications of PFs have been proposed to address challenges from both economic and environmental perspectives. The proposed development of PF technologies for economic and environmental benefits represents a comprehensive and promising approach to urban horticulture, significantly enhancing the impact and benefits of fundamental research and industrial applications.

Traditional soil cultivation of lettuce faces challenges; hydroponic technology offers solutions to improve lettuce production. However, the interrelationships among the root phenotype of lettuce, auxin synthesis and signal transduction, and nutrient solution flow, and their effects on hydroponic lettuce growth remain unclear. We investigated the effects of nutrient solution flow state on lettuce’s early growth, transcriptomic changes, and auxin-related gene expression. Growth indicators were measured 2, 4, and 6 days after transplanting. The shoot and root fresh weights, total root length, and root surface area were significantly higher under the flow treatment than under the non-flow condition. The shoot fresh weight increased by 29, 64, and 31%, respectively, at the three growth stages. A clear distinction was observed between the samples from different treatment groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that were commonly enriched included “Plant hormone signal transduction (auxin)”. Moreover, the significantly enriched Gene Ontology (GO) terms varied across different time points, which vividly reflected the dynamic characteristics of the plant’s response. Genes related to auxin biosynthesis—such as AL3F1, YUC5, and AMI4G—exhibited higher expression levels under the flow treatment. Overall, these results indicate that nutrient solution flow can promote auxin synthesis and signal transduction in early roots of lettuce.

The worldwide consumed leafy vegetable lettuce is mostly cultivated in both controlled environments and open fields, which contains various health-promoting compounds. Glycine, one of the most abundant free amino acids in soil, can be absorbed and utilized by plants. However, the sole application of glycine significantly improves lettuce quality while adversely affecting yield. Therefore, we explored a nitrogen fertilization strategy using glycine combined with nitrate, maintaining a constant total nitrogen input, to establish an approach that enhances crop quality. In this study, lettuce cultivars 'Green Lollo Rossa' and 'Red Lollo Rossa' were hydroponically cultured in nutrient solutions containing varying concentrations of glycine and nitrate. These solutions included 0 mM glycine and 9 mM NaNO3 (G0), 2.25 mM glycine and 6.75 mM NaNO3 (G2.25), 4.5 mM glycine and 4.5 mM NaNO3 (G4.5), and 6.75 mM glycine and 2.25 mM NaNO3 (G6.75). The results indicated that the G4.5 treatment induced the greatest levels of amino acids, glycosylated quercetin derivatives, luteolin derivatives, and phenolic acids, while decreasing some organic acids compared to the G0 counterparts, without biomass loss in 'Red Lollo Rossa'. While 6.75 mM glycine can improve the nutritional quality of lettuce, but it resulted in a loss in yield in 'Green Lollo Rossa'. These findings suggest that partial replacement of nitrate with an appropriate concentration of glycine can enhance the nutritional quality, and could be applied as an important strategy in lettuce cultivation by balancing the quality and yield.

Consumer demand for higher quality and nutrient-dense fresh vegetables is increasing. Therefore, superior varieties and improved cultivation methods are urgently needed to improve vegetable quality. Plant factory technology (PFT) offers an advanced agricultural system in which environmental factors may be precisely controlled, yet it remains necessary to study and predict the influence of PFT on vegetable quality due to the long breeding processes required in dynamic artificial environments. Here, a new lettuce cultivar was selected for a case study on promoting breeding processes using PFT. High-quality vegetables were produced using PFT by precisely controlling environmental factors, such as light recipes, temperature ranges, CO2 levels, and nutrients, which resulted in a higher nutritional content over a much shorter period than would occur under open-field cultivation. Consequently, PFT shows great potential in facilitating breeding and cultivation practices and achieving stable vegetable quality among harvests.

In modern agriculture, Controlled environment agriculture (CEA) stands out as a contemporary production mode that leverages precise control over environmental conditions such as nutrient, temperature, light, and other factors to achieve efficient and high-quality agricultural production. Numerous studies have demonstrated the efficacy of manipulating these environmental factors in the short period before harvest to enhance crop yield and quality in CEA. This comprehensive review aims to provide insight into various pre-harvest practices employed in CEA, including nutrient deprivation, nutrient supply, manipulation of the light environment, and the application of exogenous hormones, with the objective of improving yield and quality in horticultural crops. Additionally, we propose an intelligent pre-harvest management system to cultivate high-quality horticultural crops. This system integrates sensor technology, data analysis, and intelligent control, enabling the customization of specific pre-harvest strategies based on producers’ requirements. The envisioned pre-harvest intelligent system holds the potential to enhance crop quality, increase yield, reduce resource wastage, and offer innovative ideas and technical support for the sustainable development of CEA.

Short-term nitrogen limitation and continuous lighting (red/blue = 3:1) were applied individually and in combination to butterhead and red oak leaf lettuce for 1, 2, or 3 days before harvest to assess their effects on improving the nutritional value and sweet taste and reducing nitrate content and bitterness of lettuce. The results suggested that a 3-day nitrogen limitation combined with continuous lighting reduced the lettuce content of nitrate and sesquiterpene lactones and improved the quantities of soluble sugar, soluble protein, anthocyanins, and phenolic compounds without reducing the fresh weight of lettuce. In addition, in vitro simulated digestion results suggested that the 3-day nitrogen limitation combined with continuous lighting significantly improved the sweetness and reduced the bitterness of lettuce compared to the control. In conclusion, nitrogen limitation combined with continuous lighting for 3 days before harvest effectively enhanced the quality and taste of lettuce, showing great potential for its use in hydroponic lettuce production.

Seleno-amino acids are safe, health-promoting compounds for humans. Numerous studies have focused on the forms and metabolism of seleno-amino acids in vegetables. Based on research progress on seleno-amino acids, we provide insights into the production of selenium-enriched vegetables with high seleno-amino acids contents. To ensure safe and effective intake of selenium, several issues need to be addressed, including (1) how to improve the accumulation of seleno-amino acids and (2) how to control the total selenium and seleno-amino acids contents in vegetables. The combined use of plant factories with artificial lighting and multiple analytical technologies may help to resolve these issues. Moreover, we propose a Precise Control of Selenium Content production system, which has the potential to produce vegetables with specified amounts of selenium and high proportions of seleno-amino acids.

© The Author(s) 2022. Published by Oxford University Press on behalf of Nanjing Agricultural University. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Horticulture Research, 2022, 9: uhac018

Fruits and vegetables significantly benefit human health as they contain a large number of phytochemical compounds. Several strategies can be applied to effectively improve these health-promoting compounds by manipulating various agronomic factors. This chapter aims to provide a comprehensive understanding of how widely reported environmental factors (e.g., lighting, temperature, relative humidity, and carbon dioxide) and agronomic practices (e.g., cultivar selection, fertilizer, phytohormones, abiotic stress, and harvest time) affect the accumulation of phytochemicals in vegetables and fruits.

Background Production of biofuels and green chemicals by microbes is currently of great interest due to the increasingly limited reserves of fossil fuels. Biodiesel, especially fatty acid ethyl esters (FAEEs), is considered as an attractive alternative because of its similarity with petrodiesel and compatibility with existing infrastructures. Cost-efficient bio-production of FAEEs requires a highly lipogenic production host that is suitable for large-scale fermentation. As a non-model oleaginous yeast that can be cultured to an extremely high cell density and accumulate over 70% cell mass as lipids, Rhodotorula toruloides represents an attractive host for FAEEs production. Results We first constructed the FAEE biosynthetic pathways in R. toruloides by introducing various wax ester synthase genes from different sources, and the bifunctional wax ester synthase/acyl-CoA-diacyglycerol acyltransferase (WS/DGAT) gene from Acinetobacter baylyi was successfully expressed, leading to a production of 826 mg/L FAEEs through shake-flask cultivation. We then mutated this bifunctional enzyme to abolish the DGAT activity, and further improved the titer to 1.02 g/L. Finally, to elevate the performance of Δ ku70 - AbWS * in a bioreactor, both batch and fed-batch cultivation strategies were performed. The FAEEs titer, productivity and yield were 4.03 g/L, 69.5 mg/L/h and 57.9 mg/g (mg FAEEs/g glucose) under batch cultivation, and 9.97 g/L, 90.6 mg/L/h, and 86.1 mg/g under fed-batch cultivation. It is worth mentioning that most of the produced FAEEs were secreted out of the cell, which should greatly reduce the cost of downstream processing. Conclusion We achieved the highest FAEEs production in yeast with a final titer of 9.97 g/L and demonstrated that the engineered R. toruloides has the potential to serve as a platform strain for efficient production of fatty acid-derived molecules.

蜡酯合成酶（WS）是生物体内蜡酯合成的关键酶,存在于多种动植物和微生物中,该酶可催化生成一系列结构各异、功用不同的酯类化合物。随着对WS的深入研究,人们发现不同物种的WS在功能与活性上有较大的差异,这些差异导致了其合成产物及用途的多样性。本文系统论述了不同生物体内蜡酯的合成途径、WS的生化特性与酶工程改造及其在各种酯类化合物生产中的应用,为WS的进一步研究提供参考依据。