With the development of microbial fertilizers, efforts have been made to enrich the strain resources of plant growth-promoting rhizobacteria (PGPR) in maize and to compare the growth-promoting effects of synthetic microbial communities (SynComs) with those of single strains. To achieve this, phenotypic measurements and RNA sequencing (RNA-seq) were performed on maize roots treated with SynComs and single-strain bacterial suspensions, aiming to investigate the regulatory influence of PGPR on differential gene expression and key metabolic pathways in maize roots. In this study, 59 PGPR strains were selected, representing genera including Bacillus, Pseudomonas, Burkholderia sp., Curtobacterium pusillum, Acidovorax, Sphingobium, Mitsuaria, Bacterium, Rhodanobacter, Variovorax, Ralstonia, Brevibacillus, Terrabacter, Flavobacterium, Comamonadaceae, Achromobacter, Paraburkholderia, and Massilia. Based on the growth-promoting effects observed in pot experiments, optimal bacterial strains were selected according to the principles of functional complementarity and functional superposition to construct the SynCom. The selected strains included Burkholderia sp. A2, Pseudomonas sp. C9, Curtobacterium pusillum E2, and Bacillus velezensis F3. The results demonstrated that individual strains exerted measurable growth-promoting effects on seedlings; however, the growth-promoting capability of the SynCom was significantly stronger than that of single strains. The synthetic microbial community ALL group markedly increased root length, shoot fresh weight, shoot dry weight, number of branches, and number of root tips in maize seedlings. RNA-seq analysis of maize roots treated with the SynCom (ALL group) was conducted in comparison with CK, A2, C9, E2, and F3 treatment groups. A total of 5245 differentially expressed genes (DEGs) were identified, of which only 133 were common across treatments. GO and KEGG analyses revealed that DEGs were enriched in multiple biological processes, including cellular amide biosynthetic and metabolic processes, flavonoid biosynthetic and metabolic processes, carbohydrate metabolism, amino acid metabolism, lipid metabolism, and translation. The majority of enriched pathways were associated with primary and secondary metabolism, indicating that these bacterial strains promote plant growth by modulating a wide range of metabolic pathways in plant cells. Overall, this study provides a molecular framework for understanding the mechanisms underlying the growth-promoting effects of SynComs on maize roots and offers valuable insights for future research aimed at identifying key regulatory genes.

Spinach (Spinacia oleracea L.) is an important leafy vegetable crop, and its leaf characteristics are important for spinach germplasm innovation and new variety breeding. In this study, spinach inbred lines P₁ and P₂ were used as parents to construct six-generation segregating populations. Based on multi-location trials, we adopted an improved analytical procedure for the major gene plus polygene mixed genetic model, and the genetic models governing leaf length, leaf width and petiole length in spinach were screened. Furthermore, a high-density genetic linkage map of spinach was constructed using re-sequencing data from 152 individuals of the F₂ population, and QTLs (quantitative trait loci) governing spinach leaf type were mapped to identify their candidate genes. The results showed that the optimal genetic model for leaf length was MX1-AD-ADI, for leaf width was MX1-AD-ADI, and for petiole length was MX2-ADI-AD. The genetic map developed from the F₂ segregating population contained 5900 bin markers assigned to six linkage groups, spanning a total genetic distance of 843.48 cM. One QTL associated with leaf length was mapped on chromosome 2 and designated qLL2-1, yet no candidate genes were identified within its candidate interval. Two QTLs controlling leaf width were mapped on chromosome 1 and chromosome 2, designated qLW1-1 and qLW2-1, respectively, and 15 genes were annotated in this candidate region. One QTL related to petiole length was located on chromosome 2 and named qPL2-1, with four genes annotated in its candidate interval. Combined with spinach genome annotation and expression-level analysis of candidate genes, the gene SOV2g023140 was identified as the candidate gene regulating spinach leaf width, which was named SpPINL2. Meanwhile, three genes regulating petiole length constituted a gene cluster FAR1-ULP-zf-GRF, designated SpFAR1-ULP-zf-GRF.