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Diazotrophic microorganisms are free-living groups of organisms that can convert atmospheric nitrogen (N) into bioavailable nitrogen for plants, which increases crop development and production. The purpose of the current study was to ascertain how diazotrophic plant growth promoting (PGP) Pseudomonas strains (P. koreensis CY4 and P. entomophila CN11) enhanced nitrogen fixation, defense activity, and PGP attributes of sugarcane varieties; GT11 and G×B9. A 15N isotope-dilution study was conducted to confirm the sugarcane strains' capacity to fix nitrogen, and the results indicated that between 21 to 35% of plant, nitrogen is fixed biologically by selected rhizobacteria. In comparison to the control, after 30, 60, and 90 days, both CY4 and CN11 strains significantly increased defense-related enzymes (catalase, peroxidase, phenylalanine ammonia-lyase, superoxide dismutase, glucanase, and chitinase) and phytohormones (abscisic acid, ABA, cytokinin, etc.) in GT11 and GXB. Additionally, the expression of SuCHI, SuGLU, SuCAT, SuSOD, and SuPAL genes was found to be elevated in Pseudomonas strains inoculated plants using real-time quantitative polymerase chain reaction (RT-qPCR). Both bacterial strains increased all physiological parameters and chlorophyll content in sugarcane plants more than their control. The effects of P. koreensis CY4 and P. entomophila CN11 strains on sugarcane growth promotion and nitrogen fixation under greenhouse conditions are described here for the first time systematically. The results of confirmation studies demonstrated that P. koreensis CY4 and P. entomophila are PGP bacterial strains with the potential to be employed as a biofertilizer for sugarcane growth, nitrogen nutrient absorption, and reduced application of chemical nitrogenous fertilizers in agricultural fields. [ABSTRACT FROM AUTHOR]

Sugarcane is an important sugar and energy crop worldwide, requiring a large amount of nitrogen (N). However, excessive application of synthetic N fertilizer causes environmental pollution in farmland. Endophytic nitrogen-fixing bacteria (ENFB) provide N nutrition for plants through biological N fixation, thus reducing the need for chemical fertilizers. The present study investigated the effect of the N-fixing endophytic strain Enterobacter roggenkampii ED5 on phytohormone indole-3-acetic acid (IAA), N-metabolism enzyme activities, microbial community compositions, and N cycle genes in sugarcane rhizosphere soil at different N levels. Three levels of 15N-urea, such as low N (0 kg/ha), medium N (150 kg/ha), and high N (300 kg/ha), were applied. The results showed that, after inoculating strain ED5, the IAA content in sugarcane leaves was significantly increased by 68.82% under lowN condition at the seedling stage (60 days). The nitrate reductase (NR) activity showed a downward trend. However, the glutamine synthase (GS) and NADH-glutamate dehydrogenase (NADH-GDH) activities were significantly enhanced compared to the control under the high N condition, and the GS and NR genes had the highest expression at 180 and 120 days, respectively, at the low N level. The total N content in the roots, stems, and leaves of sugarcane was higher than the control. The 15N atom % excess of sugarcane decreased significantly under medium N condition, indicating that the medium N level was conducive to N fixation in strain ED5. Metagenome analysis of sugarcane rhizosphere soil exhibited that the abundance of N-metabolizing microbial richness was increased under low and high N conditions after inoculation of strain ED5 at the genus level, while it was increased at the phylum level only under the low N condition. The LefSe (LDA > 2, p < 0.05) found that the N-metabolism-related differential microorganisms under the highNcondition were higher than those undermedium and low N conditions. It was also shown that the abundance of nifDHK genes was significantly increased after inoculation of ED5 at the medium N level, and other N cycle genes had high abundance at the high N level after inoculation of strain ED5. The results of this study provided a scientific reference for N fertilization in actual sugarcane production. [ABSTRACT FROM AUTHOR]

Sugarcane is an important sugar and bioenergy source and a significant component of the economy in various countries in arid and semiarid. It requires more synthetic fertilizers and fungicides during growth and development. However, the excess use of synthetic fertilizers and fungicides causes environmental pollution and affects cane quality and productivity. Plant growth-promoting bacteria (PGPB) indirectly or directly promote plant growth in various ways. In this study, 22 PGPB strains were isolated from the roots of the sugarcane variety GT42. After screening of plant growth-promoting (PGP) traits, it was found that the DJ06 strain had the most potent PGP activity, which was identified as Pseudomonas aeruginosa by 16S rRNA gene sequencing. Scanning electron microscopy (SEM) and green fluorescent protein (GFP) labeling technology confirmed that the DJ06 strain successfully colonized sugarcane tissues. The complete genome sequencing of the DJ06 strain was performed using Nanopore and Illumina sequencing platforms. The results showed that the DJ06 strain genome size was 64,90,034 bp with a G+C content of 66.34%, including 5,912 protein-coding genes (CDSs) and 12 rRNA genes. A series of genes related to plant growth promotion was observed, such as nitrogen fixation, ammonia assimilation, siderophore, 1-aminocyclopropane-1-carboxylic acid (ACC), deaminase, indole-3-acetic acid (IAA) production, auxin biosynthesis, phosphate metabolism, hydrolase, biocontrol, and tolerance to abiotic stresses. In addition, the effect of the DJ06 strain was also evaluated by inoculation in two sugarcane varieties GT11 and B8. The length of the plant was increased significantly by 32.43 and 12.66% and fresh weight by 89.87 and 135.71% in sugarcane GT11 and B8 at 60 days after inoculation. The photosynthetic leaf gas exchange also increased significantly compared with the control plants. The content of indole-3-acetic acid (IAA) was enhanced and gibberellins (GA) and abscisic acid (ABA) were reduced in response to inoculation of the DJ06 strain as compared with control in two sugarcane varieties. The enzymatic activities of oxidative, nitrogen metabolism, and hydrolases were also changed dramatically in both sugarcane varieties with inoculation of the DJ06 strain. These findings provide better insights into the interactive actionmechanisms of the P. aeruginosa DJ06 strain and sugarcane plant development. [ABSTRACT FROM AUTHOR]

Diazotrophic plant growth-promoting endophytic (DPGPEB) bacterium plays an important role in plant growth and development. However, the molecular mechanism of the interaction between DPGPEB and sugarcane is still less known. In this study, we used the RNA sequencing technology to compare the transcriptome of two sugarcane varieties GT11and B8 inoculated with Enterobacter roggenkampii ED5. The results showed that a total of 1905 differentially expressed genes (DEGs) were obtained in the ED5 inoculated plants as compared to the control for variety GT11, of which 812 were down-regulated and 1093 were up-regulated, respectively. Whereas, for variety B8, 6214 DEGs were detected in the ED5 inoculated plants as compared to the control, of which 1587 and 4627 of down-regulated and up-regulated, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed the DEGs were associated with starch and sucrose, nitrogen metabolism, biosynthesis of phenylpropanoid, phytohormone signal transduction, MAPK signaling pathway, secondary metabolic pathway, cell wall biogenesis, and photosynthesis. Additionally, the results of RNA-seq data were validated with qRT-PCR. In summary, these results provide valuable information about the transcriptomic changes of the two sugarcane varieties in response to E. roggenkampii ED5 for understanding the molecular mechanisms of sugarcane-bacteria interactions. [ABSTRACT FROM AUTHOR]