Genomic and functional analyses reveal Pseudomonas granadensis CT364 is a plant growth-promoting endophyte.

BACKGROUND: Plant-associated endophytes offer promising agricultural, environmental, and biotechnological applications. Despite their potential utility, difficulties in culturing these microorganisms under laboratory conditions have limited both their isolation and a comprehensive understanding of their biology, function, and ecological role. Against this background, Pseudomonas granadensis strain CT364-isolated from the olive tree rhizosphere-emerged as a potential endophyte of interest due to its cultivability and its ability to promote rooting across diverse species, including olive trees, rapeseed, mung bean and cowpea. RESULTS: Genome Annotation and in silico predictions identified 564 genes linked to rhizosphere competence, plant colonisation and plant growth-promoting traits. Experimental findings confirmed the strain's motility, capacity for biofilm formation, and ability to sense and respond to plant-derived signals. P. granadensis CT364 effectively colonises the rhizosphere, rhizoplane, and internal tissues of Arabidopsis, confirming its endophytic nature without exhibiting any pathogenic traits. Inoculation experiments demonstrated significant effects on root architecture and increases in plant biomass and rosette area. Notably, these benefits were retained under salinity and osmotic stress, underscoring its plant growth-promoting ability. Finally, both genome analysis and experimental tests confirmed its resistance to osmotic stress and heavy metal toxicity, highlighting the strain's ability to survive in difficult environments. CONCLUSIONS: The integration of genomic insights and experimental validation supports the conclusion that P. granadensis CT364 is a plant growth-promoting endophytic bacterium. Its ability to enhance plant development under both optimal and stressful conditions, combined with its ability to colonise Arabidopsis and non-pathogenic nature, positions this strain as a potential bioinoculant for sustainable agriculture. Furthermore, the identification of specific genes related to plant sensing and colonisation, and its genetic tractability, open avenues for exploring underlying mechanisms of plant-microbe interactions. In summary, P. granadensis CT364 therefore not only holds potential for improving crop performance under challenging environmental conditions but also offers a valuable model for the study of beneficial plant-bacterial symbiosis.