Phosphate-Solubilizing Pseudomonas sp. Strain P34-L Promotes Wheat Growth by Colonizing the Wheat Rhizosphere and Improving the Wheat Root System and Soil Phosphorus Nutritional Status

Rhizosphere colonization is a requirement for field applications of plant growth-promoting rhizobacteria (PGPR). Complex signal exchanges and mutual recognition occur between microbes and plants. Here, the phosphate-solubilizing strain Pseudomonas sp. P34, which is a type of PGPR with affinity to wheat, was isolated from a wheat rhizosphere via wheat germ agglutinin. A pTR102 plasmid harboring the luciferase luxAB gene was transferred into P34. The labeled strain (P34-L) was then used to track the temporal and spatial characteristics of rhizosphere colonization and examine the effects of colonization on wheat development. The transcript levels of the phosphate transporter gene TaPT4, a phosphorus deficiency indicator, in wheat roots were monitored by quantitative reverse transcription PCR (qRT-PCR). The results indicated that P34-L could survive within the wheat rhizosphere for a long time and colonize new spaces in the wheat rhizosphere following the elongation of wheat roots. Compared with uninoculated wheat plants, plants inoculated with P34-L exhibited significantly increased phosphorus accumulation in the leaves; seedling and root weight; total root length; root projection area; root surface area; and number of root tips, forks, and crossings, thus demonstrating the great value of applying this strain in wheat production by promoting root growth and dry matter accumulation. The downregulation of TaPT4 transcript levels in the wheat roots also suggested that a high-phosphorus environment was established by P34-L. These results lay a foundation for further research on the relationships between PGPR and their host plants. Moreover, a potentially ideal biofertilizer-producing strain for use in sustainable agriculture was developed.