Plant Growth-Promoting Rhizobacteria (PGPR) are beneficial microorganisms that colonize plant root zones. They promote plant growth and enhance resistance to abiotic stresses such as drought and salinity by producing hormones, solubilizing nutrients, and other mechanisms. Currently, approximately 20% of global arable land is affected by abiotic stresses, and this proportion is projected to rise to 45% by 2050, posing a severe threat to food security. However, the specific metabolites through which PGPR exert stress-resistant effects and how these metabolites help plants cope with stresses have long been focal points of research—could these metabolites become effective tools for improving crop stress tolerance and advancing sustainable agriculture?
Professor Andi KURNIAWAN from the Faculty of Agriculture, Universitas Brawijaya, Indonesia, and his colleagues conducted a study to address this question. They isolated three PGPR strains (RK1, RT2, RT3) from the roots of tomato (Solanum lycopersicum) and potato (Solanum tuberosum) plants. The metabolite profiles of these strains were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS), and lettuce (Lactuca sativa) was used as a model to evaluate the strains' efficacy in alleviating drought stress. The related research has been published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2025667).
The study revealed that these strains produce a variety of key metabolites, including amino acids such as proline, glycine, and glutamine, as well as vitamins like biotin, pantothenic acid, and riboflavin. Among these, proline was the most abundant and served as a crucial osmoprotectant, helping plants regulate osmotic pressure and stabilize cellular structures under drought conditions.
Experimental results showed that lettuce plants inoculated with PGPR strains exhibited significantly higher survival rates and better fresh weight recovery after drought stress compared to the uninoculated control group. Specifically, lettuce treated with the RT3 strain achieved the highest survival rate, while those treated with the RT2 strain showed the best fresh weight recovery. Metabolic pathway analysis further indicated that these metabolites are involved in critical plant processes such as nitrogen metabolism, protein synthesis, and energy production. For instance, the glycine, serine, and threonine pathway is closely associated with nucleic acid synthesis and cellular energy supply, while flavonoids like luteolin help mitigate oxidative damage.
Notably, different strains displayed distinct responses to stresses: the RT2 strain showed greater variability in metabolite concentrations under oxidative stress, whereas the RT3 strain exhibited a stronger response to drought and salinity stress. This suggests that researchers can select appropriate strains based on specific stress types to optimize the effectiveness of microbial inoculants.
This study clarifies the specific roles of PGPR metabolites in plant stress resistance and provides a scientific basis for the development of high-efficiency microbial inoculants. These findings contribute to improving crop yield and stability under stressful environments, offering promising prospects for sustainable agriculture and crop protection against abiotic stresses in the future.