For decades, scientists have known that certain plant growth-promoting rhizobacteria (PGPR) enhance crop performance through various mechanisms—producing hormones, solubilizing nutrients, or suppressing pathogens.
Yet the specific chemical signals that mediate these beneficial interactions, particularly in woody perennial crops like citrus, have remained largely elusive. Based on these challenges, there is a clear need for in-depth research into the molecular dialogue between citrus and its rhizosphere microbiome.
Now, a team led by researchers at Huazhong Agricultural University in China, in collaboration with the University of Maryland, has identified a key player in this dialogue. Publishing (DOI: 10.1093/hr/uhag071) on February 28, 2026, in Horticulture Research, the scientists show that a dominant citrus rhizobacterium, Burkholderia strain Burk_2H3, promotes plant growth by secreting N-(3-oxo-octanoyl)-L-homoserine lactone—a molecule they named PGPHL—which significantly enhances nutrient uptake across multiple crop species.
Citrus rhizosphere
The research team began by isolating Burk_2H3 from citrus rhizosphere soils across 15 distinct growing sites. Metabolomic profiling revealed that PGPHL was 9.7 to 17.2 times more abundant in the secretions of this growth-promoting strain than in three non-promoting Burkholderia strains.
When applied exogenously, PGPHL increased citrus seedling dry weight by 43.12%. Transcriptomic analysis showed that Burk_2H3, its cell-free supernatant, and PGPHL all consistently upregulated key nutrient transporter genes in citrus roots—including FhNRT2.1 for nitrate, FhPHO1.1 and FhPHO1.2 for phosphate, and FhHAK5 and FhKT2 for potassium. Ion analysis confirmed that treated roots accumulated significantly higher levels of nitrogen, phosphorus, and potassium.
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Interestingly, the mechanism appears to differ from that reported in Arabidopsis, where similar molecules act through G protein-coupled receptor (GPCR) signaling—no such response was observed in citrus, suggesting a distinct pathway.
Master switch
The authors said, “We were surprised to find that a single bacterial signal could coordinate the uptake of multiple nutrients at once. Instead of acting like a hormone, PGPHL seems to flip a master switch that tells the root to bring in more of what it needs.” They added, “What excites us most is that this isn’t just a lab phenomenon—it works in the field, across different crops and soil conditions.”
The implications are substantial. Unlike live PGPR, which often suffer from poor viability, storage instability, and inconsistent field performance, PGPHL is a small, stable molecule that can be synthesized and applied directly. Field trials demonstrated that a 10 μM PGPHL solution increased pepper yield by 20.79%, mustard biomass by 14.54%, and celery biomass by 18.31%.
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This broad-spectrum efficacy suggests PGPHL could be developed into a new class of plant growth stimulants and biofertilizers, offering farmers a reliable, cost-effective tool to reduce chemical fertilizer dependence while boosting productivity. The team has already developed a synthetic route for large-scale production, bringing this microbial signal one step closer to the field.
This work was supported by the National Key Research and Development Program of China (2024YFD2300800), the National Natural Science Foundation of China (32502615), Hubei Fruit Industrial Technology System Project (2025HBSTX4-08), the Fundamental Research Funds for the Central Universities (2662025YLPY010), Hubei Provincial Citrus Industry Chain Project (2024), Guangxi Science and Technology Major Project (GK AA23062085).
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