Li-Tao Yang

Endophytic nitrogen-fixing Klebsiella variicola strain DX120E promotes sugarcane growth

Klebsiella variicola bacteria are found in association with plants. Little is known about their colonization patterns, roles, and mechanisms during association with the plant hosts. Here, we identified a nitrogen-fixing bacterium, DX120E, which was isolated from surface-sterilized roots of the ROC22 sugarcane cultivar, as K. variicola by phylogenetic analyses of its 16S rRNA gene, RNA polymerase β-subunit gene, and DNA gyrase subunit A gene sequences. gfp-tagged DX120E was found to colonize at the roots and aerial parts of micropropagated sugarcane plantlets by fluorescence microscopy and confocal microscopy. DX120E was able to survive in soils and colonize in root epidermal cells, intercellular spaces in root cortices, and leaf mesophyll and vascular tissues. DX120E preferentially colonized at root maturation and elongation zones and entered roots via cracks at the emergence site of lateral roots and at disrupted epidermis. DX120E may penetrate root epidermal cells with the aid of their cellulose-degrading enzymes. 15N isotope dilution assay demonstrated that DX120E was able to fix N2 in association with ROC22 sugarcane plants under gnotobiotic condition. DX120E was also able to promote GT21 cultivar growth and plant uptake of N, P, and K under greenhouse condition. Together, this study for the first time shows that a K. variicola strain is able to colonize in its sugarcane plant hosts, to fix N2 in association with plants, and to promote plant growth.

Differential expression profiles and pathways of genes in sugarcane leaf at elongation stage in response to drought stress.

Water stress causes considerable yield losses in sugarcane. To investigate differentially expressed genes under water stress, a pot experiment was performed with the sugarcane variety GT21 at three water-deficit levels (mild, moderate, and severe) during the elongation stage and gene expression was analyzed using microarray technology. Physiological parameters of sugarcane showed significant alterations in response to drought stress. Based on the expression profile of 15,593 sugarcane genes, 1,501 (9.6%) genes were differentially expressed under different water-level treatments; 821 genes were upregulated and 680 genes were downregulated. A gene similarity analysis showed that approximately 62.6% of the differentially expressed genes shared homology with functional proteins. In a Gene Ontology (GO) analysis, 901 differentially expressed genes were assigned to 36 GO categories. Moreover, 325 differentially expressed genes were classified into 101 pathway categories involved in various processes, such as the biosynthesis of secondary metabolites, ribosomes, carbon metabolism, etc. In addition, some unannotated genes were detected; these may provide a basis for studies of water-deficit tolerance. The reliability of the observed expression patterns was confirmed by RT-PCR. The results of this study may help identify useful genes for improving drought tolerance in sugarcane.

Complete genome sequence of Kosakonia sacchari type strain SP1T

Kosakonia sacchari sp. nov. is a new species within the new genus Kosakonia, which was included in the genus Enterobacter. K. sacchari is a nitrogen-fixing bacterium named for its association with sugarcane (Saccharum officinarum L.). K. sacchari bacteria are Gram-negative, aerobic, non-spore-forming, motile rods. Strain SP1T (=CGMCC1.12102T=LMG 26783T) is the type strain of the _K. sacchari sp. nov and is able to colonize and fix N2 in association with sugarcane plants, thus promoting plant growth. Here we summarize the features of strain SP1T and describe its complete genome sequence. The genome contains a single chromosome and no plasmids, 4,902,024 nucleotides with 53.7% GC content, 4,460 protein-coding genes and 105 RNA genes including 22 rRNA genes, 82 tRNA genes, and 1 ncRNA gene.

Transformation of sugarcane with ACC oxidase antisense gene

The present study is an attempt to validate the function of sugarcane ACO by construction of plant expression vectors for sugarcane ACO sense and anti-sense genes and their effective transformation. Plant expression vectors for sugarcane ACO anti-sense gene was constructed and then transformed into sugarcane variety ROC22 mediated by Agrobacterium tumefaciens. The transgenic shoots were screened under the selective pressure of 40 mg/l G418 and 300 mg/l cefalexin and 19 resistant plants were obtained, two of which were further proved to be positive through detecting NPTII by PCR. The transformation rate was found 10.5%. The positive plants were found to grow slowly and were more dwarf compared to non-transgenic ones. The present work reveals the efficient genetic transformation system and development of transgenic sugarcane plant with ACO antisense gene. This work will help in understanding the ethylene and growth relationship and will also help breeders in breeding programs tailored to develop new varieties using molecular approaches.

Physiological and Biochemical Characteristics Related to Cold Resistance in Sugarcane

In order to screen the cold tolerant sugarcane varieties, in Ziyuan County, one of the coldest counties having longest duration for frost and snow, in Guangxi province we comprehensively evaluated 21 sugarcane varieties using subordinate function method combined with correlation analyses based on six physiological and biochemical indexes relevant to cold tolerance under natural conditions. It was found that different sugarcane varieties had different responses to the long duration of continuous cold stress, which were dull for soluble protein, proline and malondialdehyde contents. Based on the analysis by subordinate function method, we divided the tested varieties into three groups of cold tolerance. The group I had four varieties with high cold tolerance, the group II had ten varieties with moderate cold tolerance, and the group III had seven varieties with low cold resistance. It is feasible to evaluate the cold resistance at processing maturing stage by using subordinate function method with multiple physiological and biochemical indexes, which can reveal the differences of cold hardiness in different sugarcane varieties, and provide good references for commercial sugarcane production.

Identification of a new nitrogen fixing endo-bacterium strain isolated from sugarcane stalk

A bacterial strain B8S, with nitrogen fixation ability, was isolated from the stalk of sugarcane variety RB867515 introduced from Brazil. This strain was identified based on morphological, physiological and biochemical characteristics and 16S rRNA gene sequence analysis. The 16S rRNA gene sequence analysis showed that the fragment sequence length was 1403bp. When compared withAgrobacterium tumefaciens (AY51349, AB116668.1 and AJ1307119) in GenBank, the homology of the nucleotides was 100%. Certain physiological and biochemical characteristics of new bacterium strain B8S were almost the same as that ofAgrobacterium tumefaciens. Based on its nitrogen fixation ability, the strain B8S was named asAgrobacterium diazotrophicus.

Complete genome sequence of endophytic nitrogen-fixing Klebsiella variicola strain DX120E

Klebsiella variicola strain DX120E (=CGMCC 1.14935) is an endophytic nitrogen-fixing bacterium isolated from sugarcane crops grown in Guangxi, China and promotes sugarcane growth. Here we summarize the features of the strain DX120E and describe its complete genome sequence. The genome contains one circular chromosome and two plasmids, and contains 5,718,434 nucleotides with 57.1% GC content, 5,172 protein-coding genes, 25 rRNA genes, 87 tRNA genes, 7 ncRNA genes, 25 pseudo genes, and 2 CRISPR repeats.

Intercropping in Sugarcane Cultivation Influenced the Soil Properties and Enhanced the Diversity of Vital Diazotrophic Bacteria

Soil survey was conducted at four different locations of Guangxi, China to investigate the effect of peanut and soybean inter-cropping in sugarcane cultivation on the soil properties and diazotrophic bacterial diversity. Principal component analysis result shown (PCA) showed difference impact of intercropping and monoculture on the basis of biological and chemical properties of soil. Two-way analysis of variance of soil properties showed a significant interactive effect with locations and cultivation systems. Microbial enumeration results demonstrated that intercropping system enhanced the diazotrophic population. After isolation of diazotrophs, 21 selected bacteria were characterized by siderophore, phosphate, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and nitrogenase assay. Among the identified bacteria, isolate MYSP104 showed maximum nitrogenase activity and isolate MYSS78 showed maximum ACC deaminase activity. Partial 16S rRNA gene sequencing results classified these diazotrophs in six phyla (Firmicutes, α, β, Υ-proteobacteria, actinobacteria and bacteroidetes). Diazotrophs such as Bacillus tequilensis, Variovorax paradoxus, Acidovorax facilis, Leucobacter aridicollis, Streptomyces fimicarius and Pseudomonas nitroreducens were reported for the first time from the sugarcane rhizosphere of Guangxi, China. Venn diagram explained that seven bacterial species (Brevibacterium, Burkholderia, Delftia, Leucobacter, Pseudomonas, Sinorhizobium and Variovorax) were recognized with soybean and sugarcane intercropping cultivation systems. This study concluded that intercropping system could enhance the population of N-fixers in soil. Soybean intercropping influenced the soil chemical and biological properties better than peanut. Moreover, the isolated diazotrophs need further characterization and they might be utilized as bio-inoculums for commercial sugarcane production in the future.

Research and Development Priorities for Sugar Industry of China: Recent Research Highlights

The major purpose of sugarcane production is for sugar in China. The major limits for sugar productivity include abiotic and biotic factors. Drought is the most important abiotic limit while smut and borer are the most important biotic constraints. In practice, high nitrogen fertilizer input causes high production cost and agricultural environment pollution, which also has been paid high attention to research and development priorities for sugar industry of China include breeding highly productive, high sugar, strongly resistant and nitrogen efficient sugarcane cultivars by conventional and biotechnological approaches, developing low cost and efficient cultivation technologies for sugarcane production, crossing parents innovation by utilizing wild germplasm. Whole sugarcane genome sequencing, proteome analysis and biological nitrogen fixation research are also under way.

Combined application of NPK on yield quality of sugarcane applied through SSDI

Field experiments were conducted to study the effects of combined application of nitrogen (N), phosphorus (P) and potassium (K) on growth, yield quality and nutrient balance of sugarcane with subsurface drip irrigation by using the sugarcane variety ROC89/1626 and adopting “3414” project design. It was observed that the appropriate rate of N, P2O5 and K2O increased the plant height, cane yield and cane quality of sugarcane under the experimental conditions. The fertigation model recommended for highest cane yield was 367.2 kg N, 162.6 kg P2O5 and 423.3 kg K2O per ha. The highest cane yield recorded with this dose was 101.8 t/ha. The best fertigation model recommended was 340.1 kg N, 141.9 kg P2O5 and 401.1 kg K2O per ha for the cane yield of 101.6 t/ha.