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Trichoderma spp. can enhance plant resistance against a wide range of biotic stressors. However, the fundamental mechanisms by which Trichoderma enhances plant resistance against Meloidogyne incognita, known as root-knot nematodes (RKNs), are still unclear. Here, we identified a strain of Trichoderma asperellum (T141) that could effectively suppress RKN infestation in tomato (Solanum lycopersicum L.). Nematode infestation led to an increase in the concentrations of reactive oxygen species (ROS) and malondialdehyde (MDA) in roots but pre-inoculation with T141 significantly decreased oxidative stress. The reduction in ROS and MDA was accompanied by an increase in the activity of antioxidant enzymes and the accumulation of flavonoids and phenols. Moreover, split root test-based analysis showed that T141 inoculation in local roots before RKN inoculation increased the concentration of phytohormone jasmonate (JA) and the transcripts of JA synthesis and signaling-related genes in distant roots. UPLC-MS/MS-based metabolomics analysis identified 1051 differentially accumulated metabolites (DAMs) across 4 pairwise comparisons in root division test, including 81 flavonoids. Notably, 180 DAMs were found in comparison between RKN and T141-RKN, whereas KEGG annotation and enrichment analysis showed that the secondary metabolic pathways, especially the flavonoid biosynthesis, played a key role in the T141-induced systemic resistance to RKNs. The role of up-regulated flavonoids in RKN mortality was further verified by in vitro experiments with the exogenous treatment of kaempferol, hesperidin and rutin on J2-stage RKNs. Our results revealed a critical mechanism by which T141 induced resistance of tomato plants against the RKNs by systemically promoting secondary metabolism in distant roots., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Cadmium (Cd) is a toxic heavy metal, increasingly accumulating in the environment and its presence in various environmental compartments represents a significant risk to human health via the food chain. Epigallocatechin-3-Gallate (EGCG) is a prominent secondary metabolite, which can safeguard plants from biotic and abiotic stress. However, the role of EGCG in flavonoid synthesis, nutrient acquisition and reactive oxygen species (ROS) metabolism under Cd stress remains unclear. Here, we examined the effects of EGCG and Cd treatment on leaf photochemical efficiency, cell ultrastructure, essential element acquisition, antioxidant system, and secondary metabolism in tomato (Solanum lycopersicum L.). The results showed that O 2 •−, H 2 O 2 , and malondialdehyde levels increased after Cd treatment, but Fv/Fm decreased significantly, suggesting that Cd induced oxidative stress and photoinhibition. However, EGCG mitigated the adverse effects of Cd-induced phytotoxicity in both the roots and leaves. A decrease in ROS accumulation under EGCG + Cd treatment was mainly attributed to the significant enhancement in antioxidant enzyme activity, flavonoid content, and PHENYLALANINE AMMONIA-LYASE expression in roots. Moreover, EGCG reduced Cd content but increased some essential nutrient contents in tomato plants. Transmission electron microscopy-based observations revealed that EGCG treatment safeguards leaf and root cell ultrastructure under Cd stress. This implies that tomato plants subjected to Cd stress experienced advantageous effects upon receiving EGCG treatment. The present work elucidated critical mechanisms by which EGCG induces tolerance to Cd, thereby providing a basis for future investigations into environmentally sustainable agricultural practices in areas contaminated with heavy metals, for utilizing naturally occurring substances found in plants. • Epigallocatechin-3-gallate (EGCG) is a secondary metabolite and a potent biostimulant. • EGCG increased photochemical efficiency and alleviated Cd-induced oxidative stress. • EGCG increased uptake and translocation of essential plant nutrients under Cd stress. • EGCG enhanced Cd tolerance in roots by enhancing antioxidant enzymes and flavonoids. • EGCG alleviated Cd phytotoxicity in leaves by GSH-dependent detoxification mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Trichoderma strain TH effectively suppressed root-knot nematodes (RKNs) in tomato. • TH decreased the levels of H 2 O 2 , MDA and electrolyte leakage. • TH increased the concentrations of phenols, flavonoids, lignin, cellulose JA and SA. • TH upregulated the expression of PAL , C4H, 4CL, CAD , LPO, CCOMT , Tpx1 , and G6PDH. • TH increased the activity of β-1, 3-glucanase, chitinase, protease, and amylase. Trichoderma spp. can improve plant defense against diverse plant pathogens, including fungi, bacteria, viruses, and nematodes. Nonetheless, the underlying mechanisms of Trichoderma -induced enhanced resistance, particularly against plant-parasitic root-knot nematodes (RKNs), remain poorly understood. Here, we show that T. harzianum (TH) could effectively suppress RKN (Meloidogyne incognita) infestation with an RKN reduction percentage of 61.88% in tomato plants (Solanum lycopersicum L.). While RKN infections increased the levels of reactive oxygen species (ROS; H 2 O 2 and O 2 •‾) and lipid peroxidation in tomato roots, colonization with TH significantly reduced the levels of ROS, malondialdehyde, and electrolyte leakage, which was associated with increased accumulation of multiple secondary metabolites such as flavonoids, phenols, lignin, and cellulose on 75 days after inoculation with M. incognita. Consistent with the content of secondary metabolites, the activities of enzymes related to plant defense and the expression of associated genes (PAL , C4H, 4CL, CAD , LPO, CCOMT , Tpx1 , and G6PDH) significantly increased in TH + RKN-inoculated roots compared with that in only RKN-treated roots. Moreover, TH inoculation prior to RKN infestation significantly increased the activity of pathogenesis-related (PR) proteins such as β-1,3-glucanase, chitinase, protease, and amylase by 86.31%, 36.25%, 39.78%, and 17.06%, respectively, compared with the RKN-infested roots. Furthermore, TH significantly stimulated the levels of salicylic acid and jasmonic acid. These results indicate a positive role of TH in inducing resistance against the RKNs by promoting secondary metabolism and the activity and transcripts of defense-related enzymes in tomato roots. Our study unveiled critical mechanisms of Trichoderma -induced improved resistance to RKNs, which can be useful for developing sustainable agricultural practices. [ABSTRACT FROM AUTHOR]

• Low-or high-Fe inhibited cucumber growth and induced chlorosis and oxidative stress • Melatonin alleviated oxidative stress and improved photosynthesis under iron stress • Melatonin promoted the activity and transcripts of antioxidant enzymes • Melatonin stimulated biosynthesis of secondary metabolites under iron stress • Melatonin altered Fe uptake and expression of FRO2 and IRT1 under iron stress Iron is an essential element for plants and animals; however, deficit or excess iron can result in stress on plants. In this study, we unveiled the mechanisms of shoot-based tolerance to iron toxicity by melatonin (N -acetyl-5-methoxytryptamine) in cucumber plants. Both low and high iron (Fe) supply in hydroponics decreased growth and biomass accumulation, induced chlorosis and oxidative stress, and reduced chlorophyll content, photosynthesis rate and transpiration rate in cucumber leaves. Notably, the negative effect of low-Fe was more profound than that of high-Fe treatment. However, exogenous melatonin application alleviated those inhibitions in growth, biochemical and physiological parameters, which entailed an elevation of endogenous melatonin content and a reduction of electrolyte leakage, reactive oxygen species accumulation and lipid peroxidation by improving the activity and transcripts of antioxidant enzymes and secondary metabolism-related enzymes, and concentrations of phenols and flavonoids under low and high iron conditions after melatonin treatment. Analysis of iron content in leaves and roots revealed that melatonin significantly increased the iron content under low-Fe conditions, but it decreased the same under high-Fe conditions. Moreover, melatonin increased the transcript levels of FRO2 and IRT1 under low-Fe, but it decreased those transcripts under high-Fe, suggesting that melatonin plays a dual role in iron uptake under low and high iron conditions. This study expands the stress ameliorative role of melatonin in plants and may have potential implications in agronomic management of crops in low and high iron prone soils. [ABSTRACT FROM AUTHOR]