Recently, a research team led by Prof. Yi Song at the School of Life Sciences, Southern University of Science and Technology (SUSTech), in collaboration with Prof. Jixian Zhai’s group, published a research article titled “Comparative single-nucleus RNA-seq analysis revealed localized and cell type-specific pathways governing root-microbiome interactions” in the journal Nature Communications. In this study, Arabidopsis seedlings were cultivated using the JIUPO plant growth chamber under controlled conditions (constant 23°C, 16-hour light / 8-hour dark cycle, light intensity of 100 μmol·m⁻²·s⁻¹).
To explore how plant roots differentially recognize and respond to beneficial versus pathogenic microbes, the researchers selected WCS417, a model plant growth-promoting rhizobacterium (PGPR), and GMI1000, a soil-borne pathogenic bacterium (Ralstonia solanacearum). Using a 48-well hydroponic system, they successfully constructed a high-resolution single-cell transcriptomic atlas of Arabidopsis root responses at 6 hours post-inoculation with WCS417 and GMI1000. A total of 27 distinct cell clusters were identified and integrated into 11 major root cell types. Differentially expressed genes (DEGs) were analyzed for each major cell type, and Gene Ontology (GO) enrichment analysis was performed for DEGs induced by WCS417 and GMI1000. The results revealed that roots exhibit cell type-specific and distinct early-stage responses to beneficial and pathogenic microbes.
Based on the root–WCS417 interaction map, the researchers found that the proximal meristematic zone was the main site of response to beneficial bacteria, with DEGs enriched in ribosomal and translation-related genes. This was further validated by constructing a transgenic Arabidopsis line with a ribosomal protein gene RPS2 promoter driving YFP expression, which confirmed ribosome-related gene activation specifically in the young meristematic zone upon WCS417 stimulation.
Furthermore, mutations in translation regulatory factors such as cdc123 and hem1 abolished the growth-promoting effects of WCS417. Among 13 additional ribosome biogenesis mutants tested, 6 were also found to suppress or block WCS417-induced growth promotion. These findings indicate that ribosome biogenesis and upstream translational regulators are essential for the growth-promoting activity mediated by WCS417.
Previous research has shown that root mature zones typically lose immune responsiveness to synthetic elicitors like flg22, unless combined with cellular damage. However, whether mature root tissues respond to live pathogens remained unclear. This study found that mature root zones exhibited strong immune responses to GMI1000. Further analysis revealed that immunity-related genes involved in secondary metabolite biosynthesis, such as phytoalexins, were specifically activated in mature root cells upon infection.
To validate these findings, a CYP71A12 promoter-driven YFP reporter line—a key gene in glucosinolate biosynthesis—was constructed, confirming its cell type-specific immune activation in the mature root zone.
In addition, other secondary metabolism pathways, such as terpenoid biosynthesis, also showed mature-zone specific expression in response to GMI1000. A YFP reporter line driven by the promoter of THAS1, a key gene in the thalianin (triterpene) pathway, demonstrated enriched expression in the mature cortex and non-root hair cells. Microbiome sequencing of wild-type Col-0 and thas1 mutant plants, with and without GMI1000 inoculation, revealed that THAS1 plays a role in shaping the root microbiome in response to pathogen infection.
Interestingly, the relative abundance of Oxalobacteraceae bacteria significantly increased in GMI1000-infected Col-0 roots, but not in thas1 mutants. Specific strains of Oxalobacteraceae were isolated and tested, confirming that certain enriched strains in wild-type roots offered protective effects against GMI1000, while low-abundance or non-enriched strains did not. This suggests that triterpene biosynthesis pathways like the thalianin pathway play a critical role in restructuring the root microbiome to enhance disease resistance.
Figure: Key Research Concept Diagram
Using single-nucleus RNA sequencing (snRNA-seq), the researchers established a high-resolution, cell-type-resolved map of root–microbe interactions and built a freely accessible online database for public reference: http://119.45.35.29:14333. Multiple promoter-driven reporter lines were also developed to validate the accuracy of the single-cell expression profiles.
The establishment of these high-precision single-cell interaction maps provides a new paradigm for investigating root–microbiome interactions, enabling the discovery of novel interaction genes and offering a platform to validate known root immunity genes at single-cell resolution.