Researchers in Xinjiang found that the transcription factor SlbHLH70 binds 151 drought-responsive genes, shifting hormone levels and root growth in ways that helped tomato plants recover after wilting.

A plant under drought has to make decisions: close its pores and stop losing water at the cost of growth, push roots deeper in search of moisture, or begin shutting down. Those decisions are executed by hormones, and the hormones are governed by proteins called transcription factors, which switch sets of genes on and off.

Researchers at Xinjiang University and the Xinjiang Uygur Autonomous Region Academy of Agricultural Sciences have identified one such switch in tomato and shown what happens when it is turned up or removed. Their results appear in Horticulture Research.

Tomato plants engineered to produce extra amounts of the protein, called SlbHLH70, survived drought considerably better than ordinary plants. After the soil was dried until the plants wilted and then rewatered, about 60 per cent of the overexpressing plants recovered, compared with fewer than 40 per cent of wild-type plants.

Finding the switch

The gene first drew attention because of how quickly it responded. Treating plants with PEG, a compound used to mimic drought by making water harder for roots to take up, rapidly induced SlbHLH70. So did methyl jasmonate, a hormone involved in stress and defence responses.

Its response to abscisic acid, or ABA, was more complicated. ABA is the central drought hormone in plants, accumulating when water is short and triggering the closure of stomata, the pores on leaves through which water escapes. A gene that responds to drought but not straightforwardly to ABA suggests a role that is not simply downstream of that hormone.

The protein localises to the nucleus, which is where a transcription factor needs to be to do its job of binding DNA and regulating other genes.

The name indicates the family. bHLH stands for basic helix-loop-helix, a structural motif found in transcription factors across plants, animals and fungi, in which two helical segments joined by a loop allow the protein to grip DNA and often to pair up with a partner protein. Plants carry well over a hundred such genes, and sorting out what each one does has occupied geneticists for years.

Adding and subtracting the gene

The team worked in Micro-Tom, a dwarf tomato cultivar widely used in laboratories because it is small, fast-growing and easy to transform genetically.

They made two kinds of plant. Overexpression lines carried extra copies of the gene, producing more of the protein than normal. Knockout lines had the gene disabled using CRISPR/Cas9, the gene-editing system that can be directed to cut a chosen sequence.

The pairing matters for interpretation. If adding a gene improves a trait, the gene may be sufficient to produce the effect. If removing it makes the trait worse, the gene is also necessary. Both held here: knockout plants showed more damage under drought and recovered more poorly.

One hundred and fifty-one targets

To find out what the protein actually controls, the researchers combined two techniques. DAP-seq identifies the stretches of DNA a transcription factor binds. RNA-seq measures which genes change their activity. Together they produced a list of 151 drought-responsive genes bound by SlbHLH70.

Binding was then confirmed directly for a subset using an electrophoretic mobility shift assay, a laboratory test in which a protein bound to a DNA fragment migrates differently through a gel than the fragment alone. The confirmed targets fall into two groups.

The first concerns ABA. The protein binds the promoters of SlSnRK2.1, SlPYL8, SlPP2C5 and SlCYP707A2, genes that between them sense ABA, transmit its signal and break it down. Controlling genes on both sides of that pathway means influencing not just whether the hormone is present but how strongly the plant reacts to it.

The second group concerns roots. SlCycA2;1 and SlLBD40 are involved in root development, and overexpressing plants showed stronger root growth under drought.

Hormones and roots together

Measurements by LC–MS/MS, a method that separates and identifies compounds by mass, showed altered levels of both ABA and jasmonic acid in the engineered plants.

The authors describe SlbHLH70 as a regulatory hub linking stress signals, hormone balance and root architecture. The appeal of such a hub, from a breeding perspective, is that a single change propagates into several traits at once, rather than requiring each to be modified separately.

Root growth may be the most consequential of them. A plant that extends its roots in response to drying soil can reach water that a shallow-rooted plant cannot, which is a different kind of defence from merely conserving what it already has.

Jasmonic acid, the second hormone affected, is better known for its role in defence against insects and pathogens, and its appearance in a drought study is a reminder that plant stress responses overlap. A plant has a limited budget, and the signals governing how it is spent are interconnected rather than separate.

From the greenhouse to the field

The authors are explicit that field studies are still needed to assess yield, fruit quality and performance under different drought patterns.

That caution is warranted by a long record of disappointment. Many genes that improve drought survival in controlled experiments have failed to improve yield in a field, partly because laboratory drought tests measure whether a plant lives rather than whether it produces a crop. Stress-tolerance traits also frequently carry costs: a plant that conserves water by restricting gas exchange grows more slowly even when water is plentiful.

Micro-Tom adds its own caveat. Its small size makes it convenient but unrepresentative of commercial tomato varieties, and results generally need confirming in field cultivars.

Still, drought is among the largest constraints on tomato production worldwide, and Xinjiang, where this work was done, is one of the world’s major processing-tomato regions and a notably arid one. A gene that reliably improved recovery after water stress would matter there directly.

The work was supported by the Fund for Stable Support to Agricultural Sci-Tech Renovation, the earmarked fund for XJARS, and a Xinjiang Uygur Autonomous Region project for science and technology innovation bases.

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Notes

1. “Transcription factor SlbHLH70 enhances drought tolerance in tomato.” Horticulture Research, 2026, 13(6): uhag075. DOI: 10.1093/hr/uhag075.
2. Nanjing Agricultural University The Academy of Science. “Tomato gene switch opens a path to drought-resilient crops.” EurekAlert!, 3 August 2026. https://www.eurekalert.org/news-releases/1138564.

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