Tiny root hairs, big impact: Leiden researchers uncover how bacteria help plants survive drought
plants and bacteria
Scientists at Leiden University have discovered how a beneficial bacterium helps plants cope with drought. The finding reveals a previously unknown biological pathway and could support future efforts to develop more resilient crops.
What helps plants cope better with drought? With heatwaves and periods of extreme droughts getting more and more common in all parts of the world, the need for drought-tolerant plants becomes increasingly urgent. With the help of bacteria, plants can unlock the traits that help them cope with drought, securing biodiversity and food safety.
Researchers at Leiden University have now identified a beneficial bacterium that helps plants tolerate drought. While similar effects have been reported before, the team and their collaborators went a step further by uncovering the biological mechanism behind it. The study brought together researchers from different disciplines and institutions, with first author Arezoo Rahimi at the forefront of the work and second author Sofia Stiegert making important contributions to the project.
‘We discovered a Flavobacterium that improves drought tolerance in plants,’ says plant biologist Salma Balazadeh. ‘We also uncovered one way by which the bacterium helps the plant.’ The team found that the bacterium causes the roots of plants to grow more hairs.
Screening bacteria for drought tolerance
The discovery started with a collection of bacterial strains provided by Jos Raaijmakers, Professor of Microbial Interactions and Diversity at the Leiden Institute of Biology (IBL) and the Netherlands Institute of Ecology (NIOO-KNAW). Researchers exposed plants to drought conditions and compared plants that had been treated with bacteria with those that had not. One bacterium stood out.
‘We screened a collection of bacteria to see which ones improved plant drought tolerance,’ says Balazadeh. ‘This strain was one of the most promising, so we decided to investigate it further.’
The project brought together expertise from plant biology, microbiology and molecular biology. Funding from the Dutch Research Council (NWO) helped the team continue the work and unravel the underlying mechanism.
The clue was in the roots
To understand what the bacterium was doing, the researchers looked closely at plant roots. In transparent growth systems, they noticed that plants exposed to the bacterium developed many more root hairs.
Root hairs are tiny extensions of root cells. They increase the surface area of the root, helping plants absorb water and nutrients from the soil. ‘These hairs help plants absorb water and nutrients from the soil and play an important role in how roots interact with their environment,’ Balazadeh explains. ‘The bacterium enhances their formation.’
‘Our study identifies one important pathway that is activated through the interaction between the plant and the bacterium, but there are undoubtedly many others.’
The team then uncovered the molecular chain of events behind this effect. The process involves plant signaling molecules and genes that switch other genes on and off, ultimately stimulating root hair growth.
Hidden plant abilities
Balazadeh emphasises that it is important to study plants in their natural environment. ‘There are pathways in plants that can be activated by microbes,’ she says. ‘Without these interactions, we might never discover them.’ The finding also highlights the importance of studying plants in conditions that more closely resemble the real world, where they constantly interact with microbial communities.
One piece of a larger puzzle
Balazadeh and Rahimi stress that drought tolerance is highly complex. No single gene, trait or bacterium can solve the problem on its own. ‘There is no single mechanism that determines whether a plant can withstand drought,’ they explain. ‘Our study identifies one important pathway that is activated through the interaction between the plant and the bacterium, but there are undoubtedly many others.’
Even so, understanding such mechanisms is an important step. By revealing how beneficial microbes influence plant biology, the research could eventually contribute to crop breeding and other strategies to help agriculture adapt to a warmer, drier future.
Scientific article
Rahimi, A., Stiegert, S., Karami, O. et al. Endophytic Flavobacterium promotes root hair development and enhances drought tolerance via an ERF–CEP5 hormonal regulatory module. Nat. Plants 12, 1543–1560 (2026). https://doi.org/10.1038/s41477-026-02350-4