When water runs short, plants that invest more biomass in roots relative to shoots stand a better chance of survival. A higher root-to-shoot ratio (R/S) means greater water uptake capacity and less transpirational loss—a strategy observed across diverse crops from wheat to rice to sorghum. Yet the molecular machinery that controls this critical balance has remained largely elusive. Trehalose-6-phosphate phosphatase (TPP) enzymes are known to influence sugar signaling and stress responses, but whether and how they directly modulate root-versus-shoot allocation has been unclear. Based on these challenges, there is an urgent need for in-depth research into the specific regulators that orchestrate this adaptive rebalancing.
A team led by researchers at the State Key Laboratory of Vegetable Biobreeding, Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, in collaboration with Xinjiang Agricultural University and Beijing University of Agriculture, reports (DOI: 10.1093/hr/uhag070) these findings in Horticulture Research (Volume 13, Issue 6, June 2026). The study reveals that a tomato gene called SlTPP1 acts as a positive regulator of drought tolerance by increasing root growth and elevating the R/S. Conversely, the transcription factor SlERF4 suppresses SlTPP1 expression, undermining the plant's ability to reallocate resources when water is scarce.
The researchers found that drought stress dynamically pulls SlTPP1 expression in opposite directions—ramping it up in roots while shutting it down in leaves. When they overexpressed SlTPP1 in tomato, the plants channeled more dry matter into their roots, significantly increasing the R/S and maintaining higher leaf water content under drought. At night, when sugar transport from leaves to roots peaks, SlTPP1 overexpression boosted soluble sugar accumulation in roots and upregulated a suite of cell wall biosynthesis genes, driving root elongation. Meanwhile, in leaves, SlTPP1 overexpression silenced key components of the ethylene signaling pathway, further tipping the balance toward root investment. The team then identified SlERF4 as the direct repressor of SlTPP1: this transcription factor binds to a specific element in the SlTPP1 promoter and turns off its expression. Knocking out SlERF4 with CRISPR/Cas9 released SlTPP1 from repression, boosting R/S and drought tolerance. Importantly, drought enhanced ethylene production in leaves but suppressed it in roots, creating a tissue-specific signal that drives the opposing expression of these two genes.
"The most exciting part is seeing how a single gene can coordinate such a sophisticated strategy across different organs," the authors said. "By increasing sugar accumulation in roots and dialing down ethylene signaling in leaves, SlTPP1 essentially tells the plant to invest below ground when water is scarce. And the fact that SlERF4 sits upstream as a brake on this system gives us a clear on-off switch to manipulate. We think this module could be a game-changer for breeding—not just in tomato, but potentially in other crops that rely on the same fundamental pathways."
The findings open a direct path to engineering drought-tolerant tomatoes through precision breeding or gene editing. Because SlTPP1 overexpression increases R/S without reducing total biomass, it sidesteps the yield penalty that often accompanies stress tolerance traits. The same regulatory logic may apply to other staple crops: TPP genes are conserved across plants, and ERF transcription factors are widespread regulators of stress responses. By fine-tuning this module, breeders could tailor root architecture to specific environments—deeper roots for dryland farming, for example, or more balanced partitioning for irrigated systems. As climate volatility intensifies, such targeted interventions will be essential for safeguarding food production. The study also provides a molecular framework for understanding how plants integrate sugar status, hormone signals, and organ-specific gene expression to survive drought—knowledge that could inspire entirely new strategies for crop improvement.
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References
DOI
10.1093/hr/uhag070
Original Source URL
https://doi.org/10.1093/hr/uhag070
Funding information
This research was supported by the National Key Research and Development Program of China (2023YFD2300700, 2021YFD1600300, and 2024YFD2300702), China Agriculture Research System (CARS-23-B07), and the National Natural Science Foundation of China (Grant No. 32502804).
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.