Drought is one of the most damaging abiotic stresses in crop production, reducing plant growth, development, and yield. Tomato (Solanum lycopersicum) is an economically important vegetable crop, yet its performance is strongly constrained by water deficit. Plants respond to drought through hormone signaling, stomatal regulation, osmotic adjustment, and root-system remodeling. Basic helix–loop–helix (bHLH) transcription factors are known to regulate plant development and stress responses, but the roles of many tomato bHLH genes remain poorly understood. Because of these challenges, the molecular regulators that connect drought signaling, hormone balance, and root growth in tomato require deeper investigation.
A research team from Xinjiang University and the Xinjiang Uygur Autonomous Region Academy of Agricultural Sciences reported (DOI: 10.1093/hr/uhag075) the study on March 5, 2026, in Horticulture Research. The work reveals that the SlbHLH70 gene improves tomato drought tolerance by coordinating ABA biosynthesis, abscisic acid (ABA) signal transduction, jasmonic acid (JA) accumulation, and root development, providing a candidate genetic target for breeding drought-resilient tomato varieties.
The researchers first found that SlbHLH70 was rapidly induced by polyethylene glycol (PEG), a drought-mimicking treatment, and methyl jasmonate (MeJA), while showing a complex response to ABA. The SlbHLH70 protein localized in the nucleus, supporting its role as a transcription factor. The team then created SlbHLH70 overexpressing (OE) lines and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) knockout (KO) lines in the tomato cultivar Micro-Tom. After drought and rewatering, about 60% of wilted OE plants survived, compared with less than 40% of wild-type (WT) plants, while KO plants showed stronger damage and poorer recovery. To uncover the mechanism, the team combined DNA affinity purification sequencing (DAP-seq) and RNA sequencing (RNA-seq), identifying 151 drought-responsive target genes bound by SlbHLH70. Electrophoretic mobility shift assay (EMSA) confirmed that SlbHLH70 directly binds promoters of ABA-related genes, including SlSnRK2.1, SlPYL8, SlPP2C5, and SlCYP707A2, as well as root-development genes such as SlCycA2;1 and SlLBD40. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) further showed altered ABA and JA levels, while root measurements confirmed stronger root growth in OE plants under drought.
The authors said the study places SlbHLH70 at the center of a drought-response network rather than treating it as a single-function gene. They said drought survival depends on more than keeping leaves green: plants must sense stress, adjust hormone signals, and build roots that can continue searching for water. In this framework, SlbHLH70 works like a regulatory hub, helping tomato plants connect internal stress signals with physical changes in the root system.
The findings may support future breeding strategies for tomato varieties that can better tolerate water shortage and recover after drought events. Because SlbHLH70 affects hormone pathways and root architecture, it offers both a candidate gene and a set of downstream markers for testing in broader tomato germplasm. Further field studies will be needed to evaluate yield, fruit quality, and stability under different drought patterns. Still, the study suggests that improving crop resilience may require tuning the communication between stress-response genes, hormone balance, and root growth rather than focusing on a single drought-tolerance trait.
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References
DOI
10.1093/hr/uhag075
Original Source URL
https://doi.org/10.1093/hr/uhag075
Funding information
This research was supported by Projects of Fund for Stable Support to Agricultural Sci-Tech Renovation (projects xjnkywdzc-2023001-06, xjnkywdzc-2025001-09, and xjnkywdzc-2025001-29), the earmarked fund for XJARS (project XJARS-07), and Special Project for Innovation Environment Construction in Xinjiang Uygur Autonomous Region-Construction of Science and Technology Innovation Bases (project PT2401).
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.