Three plant growth-promoting rhizobacteria from the Qinghai-Tibet Plateau enhanced plant growth and alleviated low-temperature and drought stress.

INTRODUCTION: Degradation of alpine meadows on the Qinghai-Tibet Plateau has severely restricted regional livestock development and ecological security. Exploring rhizosphere microbial resources with growth promoting and stress alleviating functions is an effective strategy for promoting grassland restoration. METHODS: In this study, three PGPR strains were isolated from the rhizosphere of Lamiophlomis rotata, a dominant species in degraded alpine meadows, and identified as Pseudomonas sp. YD4-3, Pseudomonas sp. YD4-4, and Lelliottia sp. ND3-5. Their effects on Elymus dahuricus were evaluated through germination pouch assay, low-temperature pot experiment and drought stress experiment. Whole-genome sequencing was performed on strain YD4-4, which showed the strongest effects in the experiments. RESULTS: All three strains promoted biomass accumulation and significantly improved low-temperature and drought tolerance. Strain YD4-4 exhibited the greatest effects. Whole-genome sequencing predicted that YD4-4 harbors multiple functional genes related to cold adaptation, IAA biosynthesis, nutrient transformation, and oxidative stress resistance. Genomic analyses further suggested that YD4-4 may represent a novel species within the genus Pseudomonas. DISCUSSION: This study provides microbial resources for alpine meadow restoration and the development of new biofertilizers. The genomic data of YD4-4 offer a basis for understanding how this strain promotes plant growth and alleviates stress, which may inform future strain improvement and field applications.