Engineered Rhizobium Strain Opens Transient Gene Expression to Diverse Crops

For decades, one of plant biology’s most powerful tools has been locked behind a narrow taxonomic gate. Agrobacterium-mediated transient expression—the trick of using a soil bacterium to deliver genes into plant cells for rapid, short-lived protein production—has underpinned landmark discoveries in signaling, immunity, and cell biology. Yet the standard laboratory strains that make this possible work efficiently mainly in solanaceous species such as tobacco and tomato, leaving the majority of the world’s economically important crop families without a comparable rapid assay platform. A study published in PLOS Biology now reports that an engineered strain of Rhizobium rhizogenes, designated AS109, breaks through that barrier, mediating efficient transient expression across a strikingly broad range of dicot species and consistently outperforming the workhorse agrobacterial strains on which most laboratories currently depend.

The research, led by Tolga Bozkurt and colleagues at Imperial College London together with collaborators including Chih-Horng Kuo, Erh-Min Lai, Jiorgos Kourelis, and Lida Derevnina, positions AS109 as what the authors describe as an accessible and versatile chassis for functional genomics in non-model crops. The significance of that claim lies in the widening gap it addresses. Modern genomics generates candidate genes at a pace that far outstrips the capacity of stable transformation to test them, particularly in crop species where regeneration protocols are slow, expensive, or simply unavailable. A transient expression system that works across families would allow researchers to move from hypothesis to experimental validation in days rather than seasons.

Agrobacterium-mediated transfer works by exploiting the natural ability of certain soil bacteria to smuggle DNA into plant cells. In transient expression, the delivered construct is not integrated into the genome in a heritable way; instead, it drives temporary production of a protein of interest, typically within two to five days of infiltration. This makes the technique ideal for testing protein localization, reconstituting signaling pathways, screening for molecular recognition events, and dissecting host-pathogen interactions. But host range has always been the constraint. The canonical laboratory strains, derived largely from Agrobacterium tumefaciens isolates, perform well in Nicotiana species and a handful of other solanaceous hosts, while many legumes, brassicas, and other crops respond poorly, if at all, to infection by these strains.

The PLOS Biology team systematically evaluated AS109 across diverse dicot species spanning multiple taxonomic families and found that the engineered Rhizobium strain mediated efficient transient expression where conventional strains faltered. The breadth of the host range is the headline result, but the consistency matters just as much: across the species tested, AS109 outperformed commonly used laboratory agrobacterial strains, suggesting that the advantage is not a niche adaptation to one or two unusual hosts but a general property of the strain’s interaction with plant tissue.

To demonstrate what a broad-host-range chassis makes possible, the researchers built a suite of functional assays in faba bean (Vicia faba), a legume of global agricultural importance that has long lacked accessible rapid assay tools. The assays covered protein localization, allowing researchers to see where a candidate protein travels within faba bean cells; RNA interference-mediated gene silencing, enabling targeted knockdown of endogenous genes to test function; cell-surface elicitor recognition screens, which reveal whether a plant’s immune receptors can detect molecules characteristic of invading pathogens; and nucleotide-binding leucine-rich repeat receptor, or NLR, activation, the intracellular immune signaling events that trigger programmed cell death upon effector recognition.

The fifth assay in the suite pushes into infection cell biology at the host-pathogen interface, the frontier where plant immunity research increasingly operates. Using live-cell imaging approaches refined in model solanaceous systems, researchers can now watch, in faba bean cells, how pathogens attempt to suppress defenses and how resistance proteins respond in real time. Bringing this capability to a non-model crop transforms faba bean from a species studied mainly through forward genetics and field trials into one amenable to the same mechanistic cell biology that has accelerated discovery in Arabidopsis and Nicotiana benthamiana.

Among the most consequential demonstrations is the cross-family transferability of disease-resistance genes. NLR proteins are the intracellular immune receptors that plants use to detect pathogen effectors, and engineering broad-spectrum resistance increasingly depends on moving NLRs between species. The team showed that both singleton NLRs and sensor-helper NLR pairs—two-member systems in which one receptor perceives the pathogen effector and a partner propagates the signal—originating from the Solanaceae retain their effector recognition and cell death activity when transferred into faba bean. In practical terms, this means a researcher can take a resistance gene characterized in potato or tomato and, within days, test in faba bean whether it recognizes the corresponding effector and mounts the appropriate immune response.

That result has implications well beyond faba bean. Sensor-helper NLR pairs are architecturally complex, requiring coordinated expression and physical interaction, so their successful reconstitution in a distantly related legume suggests that the cellular machinery supporting NLR signaling is more conserved across families than pessimistic assessments had assumed. For crop protection, the AS109 platform offers a rapid pre-screen: before committing years to stable transformation of a candidate resistance gene into a crop, breeders and biotechnologists can evaluate its recognition specificity and signaling competence in a transient assay, triaging candidates that would otherwise consume resources without delivering durable resistance.

The study also speaks to a structural problem in plant science. Research infrastructure has concentrated on a small number of model species, so the tools, protocols, and reference strains are optimized for them, while orphan crops and regionally important staples lag behind. The authors frame AS109 as bridging the gap between hypothesis generation and experimental validation across diverse plant species, and the phrase captures a genuine bottleneck. As genome assemblies and gene annotations accumulate for crops such as faba bean, the limiting step is no longer identifying candidate genes but testing what they do. A chassis that accepts diverse hosts converts that bottleneck from a multi-year transformation cycle into an experiment of days.

What remains to be seen is how the community adopts and extends the platform. The authors present AS109 as accessible, and its performance across families suggests immediate utility for labs working on legumes and other previously underserved dicots. Monocots, which include the cereal crops that supply the majority of human calories, present distinct barriers to Agrobacterium-mediated transfer and were not the focus of this study, so the broad-host-range claim is best understood within the dicot lineage it demonstrates. Even so, for the families it covers, the arrival of a strain that reliably outperforms standard laboratory agrobacteria across species boundaries redefines what a routine experiment in crop biology can look like—moving functional genomics for non-model crops closer to the speed and flexibility that model systems have long enjoyed.

Subject of Research: Broad-host-range Rhizobium rhizogenes-mediated transient expression for functional genomics in diverse crop species

Article Title: A broad-host-range Rhizobium rhizogenes strain enables transient expression across diverse crop species

Article References: King, F., Lopez-Agudelo, J. C., Stephens, C., Aung, M. H., Ibrahim, T., Yuen, E. L. H., Chen, A., Eilmann, N., Jenkins, S., Vuolo, C., Swee, Y.-N., Liu, W.-J., Bruty, S., Toghani, A., Kuo, C.-H., Lai, E.-M., Kourelis, J., Derevnina, L., Wu, C.-H., & Bozkurt, T. (2026). A broad-host-range Rhizobium rhizogenes strain enables transient expression across diverse crop species. PLOS Biology, 24(10), e3004010. https://doi.org/10.1371/journal.pbio.3004010

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004010

Keywords: Rhizobium rhizogenes, transient expression, Agrobacterium, faba bean, functional genomics, NLR receptors, plant immunity, crop biotechnology, gene silencing, host-pathogen interface, disease resistance, non-model crops