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Sugarcane (Saccharum spp. hybrid) is a noteworthy crop in the world for sugar and bioenergy production. In the present study, transcriptomic analysis was steered for a high sucrose mutant Guixuan B9 (GXB9) and the low sucrose mother genotype B9 of sugarcane during sugar accumulating stage. A total of 112,170 unigenes were obtained, and 106,026 (94.52%) were annotated by using the available public databases nonredundant, Gene ontology, COG, Kyoto Encyclopedia of Genes and Genomes, Swiss‐Prot, and Pfam. Functional assignment analysis of unigenes exhibited that they were active in a diversity of metabolic pathways. The vital unigenes for sucrose metabolism and accumulation were relatively characterized in the immature internodes (int. 5, 6) and maturing internodes (int. 13, 14) of GXB9 in comparison with B9. The differentially expressed unigenes (DEGs) encoding sucrose phosphate synthase (SPS, http://www.chem.qmul.ac.uk/iubmb/enzyme/EC2/4/1/14.html), sucrose synthase (SuSy, http://www.chem.qmul.ac.uk/iubmb/enzyme/EC2/4/1/13.html), and invertase (http://www.chem.qmul.ac.uk/iubmb/enzyme/EC3/2/1/26.html), which are the vital enzymes functioning in the biosynthesis and splitting of sucrose, in the internodal tissues were revealed by using Illumina Hiseq 2000 platform, and verified by quantitative reverse transcription‐polymerase chain reaction analysis. The DEGs encoding SPS proteins SPS1, SPS2, SPS4, and SPS5 were upregulated in the maturing internodes of GXB9 compared with B9. The DEGs encoding SuSy proteins were majorly upregulated in the immature internodes of GXB9, and those encoding the enzymes involved in trehalose synthesis were downregulated in GXB9 compared with B9. The results in this study have revealed the opportunities for future sugarcane improvement by concentrating on the DEGs linked to sucrose metabolic pathways by applying omics technologies.

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Plant endophytic bacteria have many vital roles in plant growth promotion (PGP), such as nitrogen (N) fixation and resistance to biotic and abiotic stresses. In this study, the seedlings of sugarcane varieties B8 (requires a low concentration of nitrogen for growth) and GT11 (requires a high concentration of nitrogen for growth) were inoculated with endophytic diazotroph Enterobacter roggenkampii ED5, which exhibits multiple PGP traits, isolated from sugarcane roots. The results showed that the inoculation with E. roggenkampii ED5 promoted the growth of plant significantly in both sugarcane varieties. 15N detection at 60 days post-inoculation proved that the inoculation with strain ED5 increased the total nitrogen concentration in the leaf and root than control in both sugarcane varieties, which was higher in B8. Biochemical parameters and phytohormones in leaf were analyzed at 30 and 60 days after the inoculation. The results showed that the inoculation with E. roggenkampii ED5 improved the activities of superoxide dismutase (SOD), catalase (CAT), NADH-glutamate dehydrogenase (NADH-GDH), glutamine synthetase (GS), and endo-β-1,4-glucanase, and the contents of proline and indole acetic acid (IAA) in leaf, and it was generally more significant in B8 than in GT11. Tandem Mass Tags (TMT) labeling and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used to perform comparative proteomic analysis in the sugarcane leaves at 30 days after inoculation with strain ED5. A total of 27,508 proteins were detected, and 378 differentially expressed proteins (DEPs) were found in the treated sugarcane variety B8 (BE) as compared to control (BC), of which 244 were upregulated and 134 were downregulated. In contrast, a total of 177 DEPs were identified in the treated sugarcane variety GT11 (GE) as compared to control (GC), of which 103 were upregulated and 74 were downregulated. The DEPs were associated with nitrogen metabolism, photosynthesis, starch, sucrose metabolism, response to oxidative stress, hydrolase activity, oxidative phosphorylation, glutathione metabolism, phenylpropanoid metabolic process, and response to stresses in Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) database. To the best of our knowledge, this is the first proteomic approach to investigate the molecular basis of the interaction between N-fixing endophytic strain E. roggenkampii ED5 and sugarcane.

Sugarcane is a significant crop plant with the capability of accumulating higher amount of sucrose. In the present study, a high sucrose content sugarcane mutant clone, GXB9, has been studied in comparison to the low sucrose mother clone B9 on morphological, agronomical and physiological level in order to scrutinize the variation because of mutation in GXB9 in field under normal environmental condition. The results showed that GXB9 has less germination, tillering rate, stalk height, leaf length, leaf width, leaf area, number of internodes, internode length and internode diameter than B9. Qualitative traits of leaf and stalk displayed significant variation between GXB9 and B9. Endogenous hormones quantity was also showed variation between the two clones. The relative SPAD reading and chlorophyll a, b concentrations also showed variation between GXB9 and B9. The photosynthetic parameter analysis indicated that the GXB9 has significantly higher net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (Tr) than B9. The qRT-PCR analysis of genes encoding enzymes like SPS, SuSy, CWIN, and CeS showed upregulation in GXB9 and downregulation in B9. However, these genes were significantly differentially expressed between the immature and maturing internodes of GXB9. The cane quality trait analysis showed that GXB9 had higher juice rate, juice gravity purity, brix, juice sucrose content and cane sucrose content than B9. The yield and component investigation results indicated that GXB9 had lower single stalk weight, however higher number of millable stalks per hectare than B9, and GXB9 had lower theoretical cane yield than B9. SSR marker analysis showed genetic variation between GXB9 and B9. This study has shown significant variation in the traits of GXB9 in comparison to B9 which advocates that GXB9 is a high sugar mutant clone of B9 and an elite source for future breeding.