As climate change intensifies drought and increases evaporative demand, agriculture faces a central challenge: how can crops use less water without sacrificing yield? A recent body of work emerging from the BARD-funded project led by Prof. Shaul Yalovsky, School of Plant Sciences and Food Security, Tel Aviv University and Prof. Julian Schroeder, University of California San Diego, provides a compelling answer: the research has identified a conserved molecular switch that improves water-use efficiency while maintaining, and in some cases even enhancing, crop performance.
The research focuses on ROP GTPases, a family of plant signaling proteins that regulate how stomata (microscopic pores on the leaf surface) open and close. Stomata are essential for carbon dioxide uptake during photosynthesis, but they are also the primary route of water loss. Striking the right balance between these two processes has long been a bottleneck in efforts to breed drought-resilient crops.
Using tomato as a model system, the researchers discovered that plants lacking a single ROP gene, SlROP9, exhibit significantly improved water use efficiency without a penalty to yield. Field trials showed that these plants lose less water through transpiration, particularly during the hottest parts of the day, yet maintain normal photosynthetic rates and fruit production. Under some reduced irrigation regimes, yields were even slightly higher than in wildtype plants.
The Slrop9 tomato mutants, along with complementary studies on cell wall architecture in Arabidopsis SlROP9homologs, show notable improvements in water conservation and water‑use efficiency. Under both field and greenhouse conditions, the Slrop9 mutants demonstrated a reduction of approximately 10–15% in total water consumption compared to wild‑type plants. In addition, they exhibited a 10–20% increase in water‑use efficiency (WUE), meaning the plants produced more biomass or fruit per unit of water lost through transpiration. Importantly, despite reduced transpiration, no yield penalty was observed, highlighting the agricultural significance of these water‑saving traits.
Mechanistically, the work revealed that ROP9 normally acts as a brake on the production of reactive oxygen species (ROS) in stomatal guard cells. When ROP9 is inactive, ROS levels increase, promoting faster and more efficient stomatal closure. This enhanced responsiveness does not shut down carbon dioxide uptake, allowing plants to conserve water while continuing to grow productively. The study also showed that this pathway operates largely independently of classical abscisic acid (ABA) signaling, adding a new layer to our understanding of plant stress responses.
Complementing these findings, a second study found that the role of ROP signaling is extended beyond stomata to xylem development and cell wall patterning in both tomato and Arabidopsis. Here, ROP proteins were shown to interact with ABA in a finely tuned “toggle switch” that controls how water-conducting tissues form and function. Advanced imaging and mathematical analyses revealed that ROP signaling helps organize the periodic patterns of secondary cell walls in xylem vessels , structures critical for efficient water transport under stress conditions.
Together, these studies highlight ROP signaling as a powerful and versatile target for crop improvement. Because ROP genes are evolutionarily conserved, the implications extend beyond tomato to a wide range of crops. Building on these discoveries, collaborations with industry are already underway to introduce ROPbased traits into commercial varieties.
In a world where every drop of water counts, this research offers a promising molecular roadmap toward more resilient, climate-ready agriculture.
Read more about this research: https://www.pnas.org/doi/10.1073/pnas.2503363122
