The work tested the containment strategy prescribed by Brazil’s National Technical Biosafety Commission for releases of genetically modified citrus. Each trial was surrounded by sequential rows of non-GM plants: citrandarin, selected for its strong ability to compete in pollination; Clemenules clementine, a self-incompatible, monoembryonic variety used as a sensitive pollen receptor and monitoring genotype; and Pera sweet orange, a self-compatible, polyembryonic commercial cultivar used to estimate the frequency of transgenic seedlings. Two rows of each genotype formed the internal and external borders. Because insects, especially bees, are the principal pollinators of citrus, the design tested whether spatial separation and pollen competition could suppress movement of genetically modified pollen toward recipient trees.

The four trials were established from 2013 through 2019 in the state of São Paulo, Brazil, with three irrigated sites in Ibaté and one rain-fed site in Santa Cruz do Rio Pardo. Rows were spaced 6.5 m apart and plants 2.5 m apart within rows. The genetically modified sweet orange carried an nptII gene cassette associated with resistance to aminoglycoside antibiotics, under either the constitutive CaMV35S or NOS promoter. The nptII marker enabled researchers to screen seedlings for evidence of pollen-mediated gene flow. Sampling occurred from 2018 through 2023, generally three to four years after each trial was planted, and included 25 to 100 open-pollinated fruits per sampled plant. Fruits were collected, their seeds extracted under aseptic conditions and germinated in nursery substrate for molecular analysis.

Marker detection was performed by conventional PCR, with confirmed transgenic tissue included as a positive control, non-GM tissue as a negative control, and no-template controls in every run. Reactions targeted nptII, using 35 cycles with denaturation at 94 °C, annealing at 62 °C and extension at 72 °C. Products were separated on 1% agarose gels and visualized under ultraviolet light. Weak or ambiguous bands led to re-extraction and duplicate analysis. Phenotype supplied an additional line of evidence: citrandarin carries a dominant trifoliate leaf trait, so trifoliate clementine seedlings indicate that citrandarin pollen fertilized the recipient flower. Microsatellite genotyping was then used to assign paternity to selected monofoliate clementine offspring that were PCR-negative for the transgene.

Controlled pollinations showed that pollen from Pera, Hamlin, Valencia and Pineapple sweet oranges, as well as Citrandarin 1600, was compatible with Clemenules clementine, producing fruit set and seed formation. In mixed-pollen treatments, however, paternity analysis indicated that citrandarin competed more effectively for fertilization than Pera or Pineapple sweet-orange pollen. Across the two controlled seasons, clementine fruits pollinated with citrandarin averaged 14.34 seeds, while Pera sweet orange averaged 16.61 seeds. These results support a mechanistic basis for the field pattern: when viable pollen is available from nearby citrandarin trees, clementine ovules can be fertilized by a source that does not carry the engineered gene, reducing the proportion of progeny that inherit it.

The field measurements nevertheless showed substantial variation among experiments, years and individual trees. Clementine border gene flow ranged from 0% to 67.24% per plant, while control trees ranged from 0% to 65.02%. Seasonal averages for the clementine border ranged from 1.89% to 19.26%, and control-tree averages ranged from 5.65% to 38.07%. Transgene was detected in progeny from 103 of 106 sampled clementine controls. Distance from the citrandarin border was positively associated with gene flow in control trees, with the overall relationship significant at p = 0.008, although annual correlation coefficients and significance values varied. The researchers linked this pattern to bee foraging, the spatial arrangement of pollen donors and changing pollen-source composition.

Environmental and management changes complicate the comparisons. Weather can affect flowering, pollen viability, nectar availability, bee movement, fruit retention and ovule fertility, while irrigation differed among the experimental areas. The study also began after the plots were planted, and trees removed because of huanglongbing disease altered both the number of recipient plants available for assessment and the relative distribution of transgenic and non-transgenic pollen sources. In one experiment, eradication reached 54.9% among Pera border plants. These shifts help explain why gene flow changed across seasons and why geographic or treatment differences cannot be interpreted as a simple, uniform effect. The central comparison—bordered plants versus clementine controls under the same broader field environment—nevertheless showed lower flow in the bordered treatment.

Pera sweet orange exhibited much lower measured flow than clementine. The transgene was detected in 15 of 3,676 sweet-orange border seedlings, giving an overall frequency of 0.31%, and no significant difference was found between the inner and outer sweet-orange rows or between the two evaluated seasons. Several biological traits may have contributed. Pera is self-compatible, allowing its own pollen to compete with pollen arriving from genetically modified donors. It is also polyembryonic: most seeds produced multiple seedlings, reflecting facultative apomixis in which maternal nucellar embryos develop alongside sexually derived zygotic embryos. Competition within the seed may favor nucellar seedlings, which do not carry transgenes carried by paternal pollen, over a zygotic embryo produced through external fertilization.

Statistical analysis found that both plant position and recipient genotype significantly influenced gene flow. Border position was associated with lower flow than the control position, and sweet orange showed lower flow than clementine. Distance also differed between the recipient groups: Pera border trees were 32.5 or 39.0 m from the nearest genetically modified parcels, whereas clementine border trees were 19.5 or 26.0 m away, so geometry as well as reproductive biology contributed to the contrast. The distance result was consistent with the proposed effect of citrandarin: in a border system, genetically modified pollen must first reach trees whose flowers can also receive abundant pollen from the non-GM superpollinator, whereas control trees were exposed more directly to donors inside the trial.

The findings do not establish a universal containment rate. The study covered specific cultivars, field sites, climates, planting configurations and management conditions, and the transgene assay measured the nptII marker rather than every possible genetic change. Although the buffer was associated with a substantial reduction in measured pollen-mediated gene flow, 15 sweet-orange seedlings and 1,656 clementine seedlings still tested positive. Citrandarin therefore mitigated rather than prevented dispersal. The authors also note that Brazil’s 2020 biosafety resolution changed the regulatory approach by requiring at least three rows of non-GM polyembryonic plants around genetically modified citrus areas, while permitting citrandarin to be omitted. The new study directly addresses the effectiveness of retaining citrandarin, showing that its competitive pollination and strategic placement were associated with substantially lower transgene frequencies under the evaluated Brazilian field conditions.

Subject of Research: Field evaluation of a citrandarin border system for containing pollen-mediated transgene flow in genetically modified sweet orange

Article Title: Field-based validation of a citrandarin buffer system for gene flow containment in genetically modified sweet orange trials

Article References: Julião, M. H. M., Jaciani, F. J., Guimarães, T. M. D. N., Sanches, A. L., Cardamoni, T. M. M., Marques, V. V., Locali, E. C., Peña, L., & Wulff, N. A. (2026). Field-based validation of a citrandarin buffer system for gene flow containment in genetically modified sweet orange trials. Frontiers in Bioengineering and Biotechnology, 14, Article 1929107. https://doi.org/10.3389/fbioe.2026.1929107

Image Credits: AI Generated

DOI: 10.3389/fbioe.2026.1929107

Keywords: citrandarin, gene flow containment, genetically modified citrus, sweet orange, pollen-mediated gene flow, biosafety, nptII marker, field trials, transgenic seedlings, Field-based, validation, buffer

Anthracnose, driven by fungal species in the genus Colletotrichum, is a persistent problem for sweet orange growers. The disease scars leaves and fruit, depresses yields, and degrades the commercial quality of harvests, and conventional management relies heavily on fungicides whose repeated use raises environmental and resistance concerns. Bacillus subtilis has long been recognized as a biocontrol agent capable of suppressing pathogens directly and of inducing host defense responses, but the host-side transcriptional mechanisms that accompany its protective effect in sweet orange remained poorly defined. The new study set out to close that gap by asking which members of the WRKY transcription factor family respond when the pathogen attacks and how those responses change when B. subtilis is applied as an intervention.

WRKY transcription factors are one of the largest families of plant-specific regulators, named for a highly conserved amino acid motif in their DNA-binding domain, and they are famous for orchestrating responses to stress, including pathogen attack. They bind promoter sequences known as W-boxes, which are enriched in the regulatory regions of many defense-related genes. To map this regulatory landscape in sweet orange, the researchers systematically searched the reference genome DVS_A1.0 and identified 55 CsWRKY family members. They then characterized the structural features of these genes and analyzed how their expression changed across an experimental system that compared healthy controls, plants infected with the anthracnose pathogen, and infected plants that also received B. subtilis treatment.

The phenotypic results were striking in their clarity. When the researchers measured lesion diameters on leaves, the infected plants that had not received the bacterium, designated the BT group, developed lesions averaging 8.72 plus or minus 0.84 millimeters. In contrast, plants in the BST group, which were infected and then treated with B. subtilis, showed lesions averaging 5.47 plus or minus 0.66 millimeters. That difference corresponds to a 37.3 percent reduction in lesion size attributable to the bacterial intervention, a magnitude of protection that is biologically meaningful for a disease that otherwise spreads aggressively through orchards.

Behind that visible symptom reduction lay an extensive transcriptional reprogramming event. Transcriptomic analysis revealed that 28 CsWRKY genes were differentially expressed when infected plants were compared with healthy controls, and 27 were differentially expressed when B. subtilis-treated infected plants were compared with infected plants alone. This near-overlapping set of responsive genes indicates that the WRKY family is broadly engaged during anthracnose infection and that the biocontrol bacterium substantially reshapes that engagement rather than acting on a single isolated pathway. The scale of the response suggests that B. subtilis does not simply kill the pathogen at the leaf surface but actively reorganizes the host’s internal defense signaling network.

To move from a list of responsive genes to a candidate regulator, the team integrated multiple lines of evidence. They examined expression patterns across treatments, constructed a predicted protein-protein interaction network to see which WRKY proteins occupied central positions in the inferred regulatory web, and validated key expression changes using reverse transcription quantitative PCR. This convergence of approaches prioritized CsWRKY40 as a candidate regulatory node. Its expression was downregulated under infection alone but restored and upregulated when B. subtilis was applied, a pattern consistent with a gene whose activity supports the protective state induced by the beneficial bacterium.

Beyond its expression dynamics, CsWRKY40 carries molecular features that hint at how its function might be controlled in the cell. The researchers used the NetPhos 3.1 tool to predict phosphorylation sites across the protein and found multiple potential sites, suggesting that CsWRKY40 could be regulated post-translationally through phosphorylation, a common mechanism by which plant cells rapidly modulate transcription factor activity during immune signaling. While the study stops short of functional validation, the presence of these predicted sites provides a concrete starting point for future experiments aimed at determining how the protein’s activity is switched on or off during the interaction between the pathogen, the bacterium, and the host.

Perhaps the most ambitious component of the study was its genome-wide promoter scan. The researchers searched the entire sweet orange genome for genes containing W-box motifs in their promoter regions and cross-referenced those candidates with the differential expression data from the BT versus CK and BST versus BT comparisons. This analysis identified 5,143 W-box-containing candidate genes that were responsive in at least one of the treatment contrasts. The team then integrated Gene Ontology, KEGG and KO orthology, NR protein database, Swiss-Prot, and protein-domain annotations to classify these candidates functionally. Of the total, 1,736 were classified as defense-associated candidates, falling into categories that include reactive oxygen species and redox homeostasis, general defense responses, hormone signaling, MAPK signaling cascades, cell wall remodeling, secondary metabolism, and pathogenesis-related functions.

That functional breadth is significant because it maps the potential downstream territory that CsWRKY40 and other responsive WRKY factors might govern. Reactive oxygen species bursts are among the earliest and most consequential events in plant immune signaling, and maintaining redox balance determines whether that burst is protective or damaging to host tissue. Hormone pathways, particularly those involving salicylic acid and jasmonic acid, cross-talk extensively to shape defense outcomes against different classes of pathogens. MAPK cascades relay signals from pathogen perception to transcriptional responses, and cell wall remodeling determines the physical barriers a pathogen must breach. Secondary metabolism supplies antimicrobial compounds, and pathogenesis-related proteins are canonical markers of induced defense. The fact that so many W-box-containing genes across these categories shifted expression in response to infection and to B. subtilis treatment suggests that the bacterium’s protective effect operates through a coordinated rewiring of multiple defense modules rather than a single linear pathway.

The authors are careful to frame CsWRKY40 as a candidate rather than a confirmed regulator, and that distinction matters. Correlation between expression patterns and phenotypic outcomes, even when supported by network predictions and qPCR validation, does not establish causation. Functional validation, whether through gene knockout, overexpression, or complementation in stable transgenic lines, will be needed to determine whether CsWRKY40 genuinely drives the protective response or simply correlates with it. Nevertheless, the study provides a well-defined starting point for such experiments and contributes a curated resource of 55 CsWRKY family members, their structural features, and their expression responses to both pathogen challenge and biocontrol intervention. For citrus growers and plant pathologists, the work adds molecular texture to a strategy that has long been used empirically in the field, and it points toward a future where beneficial bacteria might be deployed not just as living pesticides but as precision tools that engage specific host regulatory circuits to strengthen crop immunity from within.

Subject of Research: Identification of the WRKY transcription factor CsWRKY40 as a candidate regulator of Bacillus subtilis-mediated anthracnose suppression in sweet orange

Article Title: A genome-wide and transcriptome-integrated identification of CsWRKY40 as a candidate regulator associated with B. subtilis-mediated reduction of anthracnose symptoms in sweet orange

Article References: Wang, H., Ding, S., Wang, J., Pan, W., Wan, N., Sai, J., Li, Y., Zhang, L., Yao, W., Xu, R., Zhang, H., & Liu, X. (2026). A genome-wide and transcriptome-integrated identification of CsWRKY40 as a candidate regulator associated with B. subtilis-mediated reduction of anthracnose symptoms in sweet orange. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10069-9

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10069-9

Keywords: sweet orange, Citrus sinensis, anthracnose, Colletotrichum, Bacillus subtilis, WRKY transcription factors, CsWRKY40, biocontrol, transcriptomics, plant immunity, W-box, gene regulation

The scientific leadership rests with Vicent Arbona Mengual of the Department of Biology, Biochemistry and Natural Sciences at Universitat Jaume I. His team also includes Miguel González Guzmán, coordinator of the GaMBiT research group – Genetic and Metabolic Integration of Biotic and Abiotic Interactions – together with Rosario Vidal and Beatriz Julián from the Institute of Advanced Materials (INAM-UJI). The wider consortium spans 11 partners from five countries: Spain, Italy, France, Germany and Sweden. Spanish participants include the Valencian Institute for Agricultural Research and the Galician University–Business Foundation. Italy contributes the Council for Agricultural Research and Economics (CREA) and UNITEC S.p.A., while France is represented by the French Agricultural Research Centre for International Development (CIRAD), the French National Research Institute for Agriculture, Food and Environment (INRAE) and Doriane SAS. Germany’s Computomics GmbH and CYBRES GmbH join the Swedish University of Agricultural Sciences to complete the partnership.

The project’s primary biological targets are sweet orange (Citrus sinensis) and mandarin (Citrus reticulata), two species that dominate global citrus production and consumption. The central objective is to generate genetically modified lines with greater resilience to the adverse conditions caused by climate change and its exacerbating effects on pests and diseases. Rising temperatures, altered rainfall patterns and shifting pest distributions are already straining citrus orchards across the Mediterranean and beyond, making the development of hardier varieties an increasingly urgent agricultural priority. By combining stress physiology expertise with advanced genetic engineering, the consortium aims to produce trees that can maintain productivity under conditions that would compromise conventional varieties.

Resilience is only half of the project’s ambition. CitrusAld also pursues the biofortification of citrus fruits to enhance their nutritional properties. Citrus fruits are widely regarded as functional foods that combine nutritional value with health-promoting properties, thanks to their antioxidant, anti-inflammatory and cardioprotective effects. The project seeks to increase naturally occurring beneficial compounds such as flavonoids and furanocoumarins, while also introducing a compound that citrus does not normally produce: resveratrol. This stilbene, best known as a constituent of grapes and cocoa, has been selected for its cardioprotective and anti-ageing properties. If successful, the work could transform an everyday fruit into an even richer source of bioactive molecules, blurring the line between conventional nutrition and functional food design.

Identifying which genes to modify in a genome as complex as citrus is a formidable challenge, and this is where artificial intelligence enters the project. The consortium will design and implement AI-based systems capable of analysing and integrating large volumes of biological data to pinpoint the most suitable target genes for each desired modification. Rather than relying on laborious trial-and-error approaches, the researchers intend to use computational pipelines that can sift through genomic, transcriptomic and metabolic datasets to prioritise candidate genes whose manipulation is most likely to yield stress tolerance or enhanced nutritional profiles. This data-driven gene discovery methodology represents one of the project’s key methodological innovations and reflects a broader trend of machine learning reshaping plant biotechnology.

Once target genes are identified, the actual genetic modifications will be carried out using New Genomic Techniques, or NGTs, which are now permitted in Europe under the newly updated regulatory framework. These techniques allow precise edits to a plant’s genome without introducing foreign DNA in the way older transgenic methods did, and their recent regulatory acceptance in the European Union has opened the door to projects of this kind. The consortium will also integrate novel materials capable of overcoming existing biological barriers that have historically limited the genetic efficiency of citrus species. Citrus is notoriously difficult to transform genetically, with recalcitrant tissues, long generation times and barriers to regeneration, so the development of new delivery materials could prove as consequential as the gene edits themselves.

In parallel with genome editing, the consortium will explore complementary strategies based on RNA interference technology. RNAi allows researchers to slow down or silence the expression of specific genes without permanently altering the genome, offering a reversible and highly targeted means of modulating plant traits. A central technical hurdle for RNAi in plants is delivering the interfering molecules into plant tissues, where cell walls and other barriers block conventional approaches. The CitrusAld team plans to use novel materials as delivery vehicles into plant tissues, an approach that draws on the materials science expertise within the consortium and could establish new protocols for transient gene silencing in woody perennial crops.

The funding mechanism behind the project is as distinctive as its science. The EIC Pathfinder Challenges programme, part of the European Innovation Council, supports highly innovative, high-risk scientific research with the potential to generate entirely new technologies in the future. It deliberately funds the early stages of research, when ideas are still being explored in the laboratory and there is not yet a clear commercial application. The programme’s objective is to establish the scientific and technological foundations for breakthroughs that, in the long term, can transform entire sectors or help address major societal challenges. For a crop that underpins the economies of Mediterranean regions and provides vitamin-rich food to billions of people, the societal stakes of climate-resilient citrus are considerable.

The four-year project will begin in October 2026 under proposal number 101306995, giving the consortium a defined window in which to deliver its gene discovery pipelines, transformation protocols and biofortified citrus lines. The breadth of the partnership – spanning academic plant science institutes, agricultural research organisations, materials specialists and companies – suggests a deliberate effort to cover the full pipeline from fundamental gene discovery to applied field-relevant varieties. The involvement of computational firms such as Computomics and CYBRES alongside plant science heavyweights like INRAE and CIRAD signals that the AI and data integration components are treated as core infrastructure rather than an afterthought.

For consumers and growers alike, the project’s promise is twofold: citrus trees better equipped to endure a warming, pest-pressured world, and fruit with an enhanced portfolio of health-promoting compounds. Whether engineered resilience and resveratrol-enriched oranges will reach commercial orchards remains a question for the years beyond the project’s horizon, but CitrusAld represents one of the most comprehensive European attempts to marry genomics, artificial intelligence, materials science and plant breeding in service of a single iconic crop. As climate change accelerates and the tools of biotechnology mature, the humble orange may become a showcase for how 21st-century science re-engineers the foods we have cultivated for millennia.

Subject of Research: Genetic modification of citrus crops for climate resilience and nutritional biofortification

Article Title: Universitat Jaume I leads European consortium to develop genetically modified citrus lines with greater resilience to climate change, pests and diseases

Article References: Universitat Jaume I leads European consortium to develop genetically modified citrus lines with greater resilience to climate change, pests and diseases. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: citrus, genetic modification, climate change, EIC Pathfinder, Universitat Jaume I, New Genomic Techniques, RNA interference, biofortification, resveratrol, artificial intelligence, sweet orange, mandarin