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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.

Smut, the most important sugarcane fungal disease in China, is caused by Sporisorium scitamineum. Smut infection causes severe cane and sugar yield loss. Whole-plant resistance response is characterized by the expression of a large number of pathogenesis-related proteins and genes. Here, proteomic analysis by isobaric tag for relative and absolute quantification was conducted to identify differentially expressed proteins of two sugarcane varieties with contrasting resistance to smut, i.e. Yacheng71-374 (smut-susceptible) and GT29 (smut-resistant) following S. scitamineum infection. A total of 125 and 290 proteins were found differentially expressed after whip appearance in Yacheng71-374 and GT29 sugarcane varieties. Increased up-regulation of peroxidase and catalase and proteins involved in photosynthesis, calcium signaling, abscisic acid biosynthesis, and protein metabolism, were observed in GT29 as compared to Yacheng71-374, suggesting their potential involvement in smut defense mechanism(s) in sugarcane. The expression level of five important defense-related enzymes i.e. chitinase, glucanase, catalase, superoxide dismutase, and phenylalanine ammonia-lyase was analyzed by RT-qPCR. The expression of these enzymes was found enhanced considerably in GT29 as compared to Yacheng71-374 for up to six months following pathogen infection. These results provide new molecular insights into long-term responses of sugarcane to smut infection, a much over-looked aspect of sugarcane smut disease.

Sugarcane is a leading biofuel crop besides being a source of crystal sugar and biomaterials worldwide. This study chiefly focuses on the role of diazotrophic bacteria isolated from sugarcane rhizosphere exhibiting different plant growth-promoting traits and biocontrol activities. Several bacterial isolates were obtained from the rhizosphere soil samples of four sugarcane cultivars. Out of these, 23 strains were selected and identified by 16S rRNA gene sequencing which confirmed different PGP-traits, biocontrol, and nitrogenase activities with nifH gene amplification. Two prominent strains, Kosakonia radicincitans-BA1 and Stenotrophomonas maltophilia-COA2 were selected for further analysis. Biolog plate assay was used to establish the utilization of various carbon and nitrogen sources and pH and osmotic stress tolerance for both strains. Colonization of selected strains in the sugarcane plant was observed by scanning electron microscopy and confocal laser scanning microscopy exhibited bacterial cells were frequently located in sugarcane tissues. Inoculation of the strains in GT11 and GXB9 cultivars led to a significant increase in growth parameters, nitrogen content, expression of nifH, and stress-related genes under greenhouse conditions. This is the first study to explore K. radicincitans and S. maltophilia as nitrogen-fixing plant growth-promoting rhizobacteria in sugarcane for disease management and reduce the practice of chemical fertilizers.