How tomatoes balance salt stress and survival
image: Schematic model depicting the role of SlNAC2 in regulating saline–alkali stress tolerance in tomato. Following exposure to saline–alkali stress, SlNAC2 is upregulated and directly targets the SlCV promoter, leading to transcriptional activation of SlCV and increased ROS levels. In addition, SlNAC2 interacts with the promoters of SlCOMT2 and SlSNAT, resulting in transcriptional repression and a subsequent decline in endogenous MT content. The reduction in MT further enhances tomato sensitivity to salt–alkali stress. Furthermore, SlDREB2 physically interacts with SlNAC2 and modulates its transcriptional activity, reinforcing that the SlDREB2- SlNAC2 module acts as a central hub controlling saline–alkali stress responses by precisely regulating downstream genes involved in MT biosynthesis and ROS homeostasis.
Credit: Horticulture Research
Soil salinization is becoming a major constraint on crop production, especially where salt and alkaline stress strike together. A new tomato study reveals how plants balance vulnerability and defense through a molecular module that controls antioxidant capacity. The research identifies the gene SlNAC2 as a negative regulator of saline–alkali tolerance. When activated by stress, SlNAC2 suppresses melatonin (MT) biosynthesis and promotes reactive oxygen species (ROS) accumulation, making tomato plants more sensitive. Its interacting partner, SlDREB2, counterbalances this effect by weakening SlNAC2’s repression of MT-related genes and helping restore ROS homeostasis, offering a new route for stress-resilient tomato breeding.
Tomato is one of the world’s most important vegetable crops, but its productivity is highly vulnerable to saline–alkali soils. Compared with neutral salt stress alone, saline–alkali stress imposes multiple pressures at once, including osmotic imbalance, toxic ion accumulation, high pH, nutrient disruption, and oxidative damage. Although melatonin (MT) is known to help plants withstand environmental stress by strengthening antioxidant defense, how tomato controls MT production at the transcriptional level under saline–alkali conditions has remained unclear. Due to these problems, it is necessary to conduct in-depth research on the molecular networks that regulate tomato tolerance to saline–alkali stress.
Researchers from Qingdao Agricultural University, the University of California, Berkeley, and Northeast Agricultural University reported (DOI: 10.1093/hr/uhag029) the study in Horticulture Research on January 30, 2026. The work examined how a tomato NAC transcription factor, SlNAC2, and a Dehydration-Responsive Element-Binding (DREB)-type transcription factor, SlDREB2, regulate MT biosynthesis and reactive oxygen species (ROS) homeostasis under saline–alkali stress. Through genetic, physiological, biochemical, and protein-interaction analyses, the study uncovered a regulatory module that fine-tunes tomato stress sensitivity and points to candidate targets for improving crop resilience.
The study found that SlNAC2 is strongly induced by saline–alkali treatment and encodes a nuclear-localized NAC transcription factor. However, functional tests showed that this stress-induced factor acts as a brake on tolerance rather than a shield. Tomato plants overexpressing SlNAC2 showed stronger wilting, shorter roots, lower fresh weight, reduced photosystem II efficiency, higher ion leakage, and greater malondialdehyde accumulation under sodium carbonate stress. By contrast, RNA interference (RNAi)-mediated silencing of SlNAC2 improved plant performance. The mechanism centered on two connected pathways. SlNAC2 directly repressed the MT biosynthetic genes SlCOMT2 and SlSNAT, lowering endogenous MT levels, while activating SlCV, a ROS-associated gene that promotes oxidative stress. Chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR), yeast one-hybrid (Y1H), dual-luciferase, and electrophoretic mobility shift assay (EMSA) experiments confirmed that SlNAC2 binds directly to the promoters of SlCOMT2, SlSNAT, and SlCV.
The authors said the findings reveal a balancing system that helps explain how tomato plants manage stress signals. In this model, SlNAC2 increases saline–alkali sensitivity by reducing MT production and allowing ROS to accumulate, while SlDREB2 works as a molecular counterweight. Yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and co-immunoprecipitation (Co-IP) assays showed that SlDREB2 physically interacts with SlNAC2. Although SlDREB2 does not directly bind the SlCOMT2 or SlSNAT promoters, it reduces SlNAC2-mediated repression of these genes and weakens SlNAC2-driven activation of SlCV.
These findings provide a practical molecular entry point for breeding tomato varieties better suited to salt- and alkali-affected soils. Rather than focusing only on ion transport or osmotic adjustment, the study highlights a transcriptional module that connects MT biosynthesis with ROS control. Fine-tuning SlNAC2, enhancing SlDREB2, or targeting downstream genes such as SlCOMT2, SlSNAT, and SlCV could help improve stress resilience without broadly disrupting plant growth. More broadly, the SlNAC2–SlDREB2–MT–ROS pathway offers a framework for understanding how crops balance growth, defense, and survival under increasingly challenging soil conditions.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhag029
Funding information
This work was supported by the Key R&D Program of Shandong Province (2022LZGCQY001), the Shandong Agriculture Research System (SDARS-05), Qingdao Science and Technology Public Welfare Demonstration Special Project (25-1-5-xdny-13-nsh and 25-1-5-xdny-2-nsh), and the National Natural Science Foundation of China (31701063, 31770275, 32472750, and U22A20495).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.