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. 2015 Jul 19;16(1):534.
doi: 10.1186/s12864-015-1760-5.

Identification and transcriptomic profiling of genes involved in increasing sugar content during salt stress in sweet sorghum leaves

Na Sui  1 , Zhen Yang  2 , Mingli Liu  3 , Baoshan Wang  4
Affiliations

Identification and transcriptomic profiling of genes involved in increasing sugar content during salt stress in sweet sorghum leaves

Na Sui et al. BMC Genomics. .

Abstract

Background: Sweet sorghum is an annual C4 crop considered to be one of the most promising bio-energy crops due to its high sugar content in stem, yet it is poorly understood how this plant increases its sugar content in response to salt stress. In response to high NaCl, many of its major processes, such as photosynthesis, protein synthesis, energy and lipid metabolism, are inhibited. Interestingly, sugar content in sweet sorghum stems remains constant or even increases in several salt-tolerant species.

Results: In this study, the transcript profiles of two sweet sorghum inbred lines (salt-tolerant M-81E and salt-sensitive Roma) were analyzed in the presence of 0 mM or 150 mM NaCl in order to elucidate the molecular mechanisms that lead to higher sugar content during salt stress. We identified 864 and 930 differentially expressed genes between control plants and those subjected to salt stress in both M-81E and Roma strains. We determined that the majority of these genes are involved in photosynthesis, carbon fixation, and starch and sucrose metabolism. Genes important for maintaining photosystem structure and for regulating electron transport were less affected by salt stress in the M-81E line compared to the salt-sensitive Roma line. In addition, expression of genes encoding NADP(+)-malate enzyme and sucrose synthetase was up-regulated and expression of genes encoding invertase was down-regulated under salt stress in M-81E. In contrast, the expression of these genes showed the opposite trend in Roma under salt stress.

Conclusions: The results we obtained revealed that the salt-tolerant genotype M-81E leads to increased sugar content under salt stress by protecting important structures of photosystems, by enhancing the accumulation of photosynthetic products, by increasing the production of sucrose synthetase and by inhibiting sucrose decomposition.

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Figures

Fig. 1
Fig. 1
The phenotype of M-81E (a) and Roma (b) treated with different concentrations of NaCl (0, 50 and 150 mM) for 7 days
Fig. 2
Fig. 2
Effect of salt stress (0, 50 and 150 mM) on Fv/Fm and ΦPSII in leaves of M-81E and Roma. Fv/Fm and ΦPSII were measured after treated with NaCl for 7 days. Values are means ± SD of five measurements for each of five plants. Bars with the different letters are significantly different at p = 0.05 according to Duncan’s multiple range test. Bars with same letter are not significantly different
Fig. 3
Fig. 3
Chlorophyll content of M-81E and Roma treated with different concentrations of NaCl (0, 50 and 150 mM) for 7 days. Values are means ± SD of five replicates. Bars with the different letters are significantly different at p = 0.05 according to Duncan’s multiple range test. Bars with same letter are not significantly different
Fig. 4
Fig. 4
Photosynthetic rate, stomatal conductance and intercellular CO2 concentration of M-81E and Roma treated with different concentrations of NaCl (0, 50 and 150 mM) for 7 days. Values are means ± SD of five replicates. Bars with the different letters are significantly different at p = 0.05 according to Duncan’s multiple range test. Bars with same letter are not significantly different
Fig. 5
Fig. 5
Sugar content of M-81E and Roma treated with different concentrations of NaCl (0, 50 and 150 mM) for 7 days. Values are means ± SD of five replicates. Bars with the different letters are significantly different at p = 0.05 according to Duncan’s multiple range test
Fig. 6
Fig. 6
Numbers of DEGs of different genotypes affected by salt stress
Fig. 7
Fig. 7
Functional annotation of assembled sequences based on gene ontology (GO) categorization. Results are summarized for three main Go categories: Biological Process, Molecular Function, and Cellular Component
Fig. 8
Fig. 8
The heat map display of DEGs assigned to different KEGG pathways. The numbers in the scale bar show the percentage of the number of DEGs assigned to a certain KEGG pathway in which assigned to all KEGG pathways. Red indicates that more genes are enriched in this pathway
Fig. 9
Fig. 9
KEGG map of the photosynthesis pathway. It’s an analysis of DEGs, comparing salt-treated samples to untreated control. Boxes with a red frame indicate the corresponding DEGs were up-regulated in the salt-treated samples, boxes with a green frame indicate the corresponding DEGs were down-regulated in the salt-treated samples, boxes with blue frame indicate some of the corresponding DEGs were down-regulated and others were up-regulated, and those without any colored frame indicate the expression level of corresponding genes were not changed, as determined by RNA-seq
Fig. 10
Fig. 10
Validation of RNA-seq results by RT-qPCR. Expression levels of 14 randomly selected genes in the four samples used in this study were detected by RT-qPCR. R2 represents the correlation coefficient value between the two platforms. The numbers in the scale bar stand for RPKM values in RNA-seq and ΔΔCt in qRT-PCR, which were used to evaluate the correlation (R2). Primers are listed in (Additional file 9: Table S2)
Fig. 11
Fig. 11
Validation of RNA-seq results by RT-qPCR. Expression levels of 3 genes involved in sucrose synthesis and metabolism pathways were detected by RT-qPCR. R2 represents the correlation coefficient value between the two platforms. The numbers in the scale bar stand for RPKM values in RNA-seq and ΔΔCt in qRT-PCR, which were used to evaluate the correlation (R2). Primers are listed in (Additional file 9: Table S2)
Fig. 12
Fig. 12
visualization of DEGs involved in pathways related with the accumulation of sugar. A square block represents a gene assigned to our RNA-seq data. Blue represents the gene was down-regulated in salt-treated samples compared to the control samples. Red represents the gene was up-regulated. For each gene, the square block on the left stand for M-81E and the right one stand for Roma
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