Metabolite profiles of energy cane and sugarcane reveal different strategies during the axillary bud outgrowth

Differential responses of Bradyrhizobium sp. SUTN9-2 to plant extracts and implications for endophytic interactions within different host plants

Bradyrhizobium sp. strain SUTN9-2 demonstrates cell enlargement, increased DNA content, and efficient nitrogen fixation in response to rice (Oryza sativa) extract. This response is attributed to the interaction between the plant's cationic antimicrobial peptides (CAMPs) and the Bradyrhizobium BacA-like transporter (BclA), similar to bacteroid in legume nodules. The present study reveals that SUTN9-2 can also establish functional endophytic interactions with chili (Capsicum annuum) and tomato (Solanum lycopersicum) plants. When exposed to extracts from chili and tomato, SUTN9-2 exhibits cell elongation, polyploidy, and reduced cell viability, with the effects being less pronounced for tomato extract. Transcriptomic and cytological analyses revealed that genes associated with CAMP resistance, nitrogen metabolism, nitrogen fixation, defense responses, and secretion systems were upregulated, while genes related to the cell cycle and certain CAMP-resistance mechanisms were downregulated, particularly in response to chili extract. This study suggests that SUTN9-2 likely evolves resistance mechanisms against CAMPs found in rice, chili, and tomato plants through mechanisms involving the protease-chaperone DegP, AcrAB-TolC multidrug efflux pumps, and polysaccharides. These mechanisms facilitate efflux, degradation, and the formation of protective barriers to resist CAMPs. Such adaptations enable SUTN9-2 to persist and colonize host plants despite antimicrobial pressures, influencing its viability, cell differentiation, and nitrogen fixation during endophytic interactions with various plant hosts.

Endophytic nitrogen-fixing bacteria DX120E inoculation altered the carbon and nitrogen metabolism in sugarcane

Endophytic nitrogen-fixing bacteria are versatile and widely distributed in plants. Numerous strains of endophytic nitrogen-fixing bacteria are used as biofertilizers to minimize the utilization of chemical fertilizers, improve nutrient use efficiency, increase crop productivity, and reduce environmental pollution. However, the mechanism underlying the interaction between nitrogen-fixing bacteria and plants is still unclear. So, the present study was planned to assess the effects of endophytic nitrogen-fixing bacteria on sugarcane by analyzing the changes in physiological and biochemical activities. In the current study, Klebsiella variicola DX120E, an endophytic nitrogen-fixing bacterium, was inoculated on sugarcane varieties B8 and ROC22 to evaluate the effects on nitrogen and carbon metabolism-related enzymatic activity and biomass. Results showed that DX120E inoculation improved the enzymatic activities related to gluconeogenesis and nitrogen metabolism increased the sugarcane plant's height, cane juice Brix, biomass, chlorophyll, and soluble sugar content in sugarcane. Metabolomics analysis revealed that the metabolome modules were highly enriched in carbon and nitrogen metabolic pathways of strain-affected sugarcane than uninoculated control. The identified carbohydrates were associated with the glycolysis or gluconeogenesis and tricarboxylic acid (TCA) cycle in plants. Metabolomic profiling in the present investigation showed that carbohydrate metabolism is coordinated with nitrogen metabolism to provide carbon skeletons and energy to amino acid synthesis, and amino acid degradation results in several metabolites used by the citric acid cycle as an energy source. Moreover, differentially expressed metabolites of non-proteinogenic amino acids have a further complementary role to the action of endophytic nitrogen-fixing bacteria. Meanwhile, a significant difference in metabolites and metabolic pathways present in stems and leaves of B8 and ROC22 varieties was found. This study discovered the potential benefits of DX120E in sugarcane and suggested candidate regulatory elements to enhance interactions between nitrogen-fixing microbes and sugarcane.

Internode elongation in energy cane shows remarkable clues on lignocellulosic biomass biosynthesis in Saccharum hybrids

Energy cane is a dedicated crop to high biomass production and selected during Saccharum breeding programs to fit specific industrial needs for 2G bioethanol production. Internode elongation is one of the most important characteristics in Saccharum hybrids due to its relationship with crop yield. In this study, we selected the third internode elongation of the energy cane. To characterize this process, we divided the internode into five sections and performed a detailed transcriptome analysis (RNA-Seq) and cell wall characterization. The histological analyses revealed a remarkable gradient that spans from cell division and protoxylem lignification to the internode maturation and complete vascular bundle lignification. RNA-Seq analysis revealed more than 11,000 differentially expressed genes between the sections internal. Gene ontology analyzes showed enriched categories in each section, as well as the most expressed genes in each section, presented different biological processes. We found that the internode elongation and division zones have a large number of unique genes. Evaluated the specific profile of genes related to primary and secondary cell wall formation, cellulose synthesis, hemicellulose, lignin, and growth-related genes. For each section these genes presented different profiles along the internode in elongation in energy cane. The results of this study provide an overview of the regulation of gene expression of an internode elongation in energy cane. Gene expression analysis revealed promising candidates for transcriptional regulation of energy cane lignification and evidence key genes for the regulation of internode development, which can serve as a basis for understanding the molecular regulatory mechanisms that support the growth and development of plants in the Saccahrum complex.