Soil salinity is one of the major factors that affect plant growth and decrease agricultural productivity worldwide. Chitosan (CTS) has been shown to promote plant growth and increase the abiotic stress tolerance of plants. However, it still remains unknown whether the application of exogenous CTS can mitigate the deleterious effects of salt stress on lettuce plants. Therefore, the current study investigated the effect of foliar application of exogenous CTS to lettuce plants grown under 100 mM NaCl saline conditions. The results showed that exogenous CTS increased the lettuce total leaf area, shoot fresh weight, and shoot and root dry weight, increased leaf chlorophyll a, proline, and soluble sugar contents, enhanced peroxidase and catalase activities, and alleviated membrane lipid peroxidation, in comparison with untreated plants, in response to salt stress. Furthermore, the application of exogenous CTS increased the accumulation of K⁺ in lettuce but showed no significant effect on the K⁺/Na⁺ ratio, as compared with that of plants treated with NaCl alone. These results suggested that exogenous CTS might mitigate the adverse effects of salt stress on plant growth and biomass by modulating the intracellular ion concentration, controlling osmotic adjustment, and increasing antioxidant enzymatic activity in lettuce leaves.

Strawberry is one of the most highly consumed fruits worldwide, but is extremely perishable. This study systematically compared the effects of chitosan, sucrose, glucose, and fructose immersion on the physiology and disease development in harvested strawberries. After storage at 15 °C for 9 days, all sugar treatment groups had significantly higher total soluble solids and total anthocyanin content than those of the control group. All sugar treatment groups inhibited malondialdehyde accumulation. At the end of the storage, chitosan, glucose, and fructose maintained higher superoxide dismutase activity and chitosan maintained higher catalase activity. The chitosan and glucose groups had lowest fruit decay index, followed by sucrose and fructose groups. The fruit firmness and luster were better maintained in the glucose group. Furthermore, genes related to sucrose metabolism (e.g., FaSUS1 and FaSUS2), titratable acidity accumulation (e.g., FaMDH1, FaMDH2, FaCS1, and FaCS2), disease resistance (e.g., FaPGIP1, FaWRKY1, and FaWRKY33) and to anabolic jasmonic acid and abscisic acid pathways (e.g., FaJAZ1, FaJAZ2, FaOPR3, FaNCED1, and FaNCED2) were regulated to varying degrees, suggesting that chitosan and glucose participate in plants’ immune signaling networks and regulate disease resistance in fruit through hormone pathways. The findings provide new insights into the physiological regulation of harvested strawberries.

Introductions: Expansin-like proteins from Trichoderma have emerged as potential biological regulators of plant growth through their effects on cell wall properties; however, the molecular mechanisms underlying their growth-promoting effects in horticultural crops remain poorly understood. Methods: This study investigated the effects of TgSWO, an expansin-like protein from Trichoderma harzianum NJAU 4742, on strawberry (Fragaria × ananassa) root development and elucidated the underlying regulatory mechanisms. Strawberry plantlets were treated with 0, 15, or 30 μM TgSWO for 2 weeks, followed by root phenotypic characterization, transmission electron microscopy, transcriptomic profiling, and untargeted metabolomic analysis. Results: Exogenous TgSWO application significantly promoted strawberry root development, as evidenced by increased root number, root fresh weight, root length, root surface area, and root tip number. Transmission electron microscopy revealed that TgSWO treatment altered root cell morphology, indicating enhanced cellular remodeling. Transcriptomic analysis showed that low-dose TgSWO treatment primarily enhanced metabolic activity and cell wall remodeling, whereas high-dose TgSWO treatment activated redox regulation, secondary metabolism, and structural reinforcement pathways. Metabolomic analysis further demonstrated that TgSWO reshaped root metabolic profiles by regulating pathways associated with nutrient uptake, lipid metabolism, amino acid metabolism, and secondary metabolism. Key metabolites positively correlated with root biomass, including cinnamic acid and cysteine, were identified as potential contributors to TgSWO-mediated root growth promotion. Discussion: These findings reveal that TgSWO promotes strawberry root development through coordinated regulation of cell wall remodeling, transcriptional reprogramming, and metabolic adjustment, providing new insights into microbial expansin-like protein-mediated plant growth regulation and supporting the potential application of TgSWO as a functional protein-based strategy for greenhouse strawberry production.