Abstract
BackgroundSugar content is critically important in determining sugar crop productivity. However, improvement in sugar content has been stagnant among sugar crops for decades. Sorghum, especially sweet sorghum with high biomass, shown great potential for biofuel, has lower sugar content than sugarcane. To enhance sugar content, the sucrose isomerase (SI) gene, driven by stem-specific promoters (A2 or LSG) with a vacuole-targetted signal peptide, was transformed into the sorghum inbred line (T×430).ResultsThe study demonstrated that transgenic lines of grain sorghum, containing 50–60% isomaltulose, accumulated up to eightfold (1000 mM) more total sugar than the control T×430 did (118 mM) in stalks of T0 generation. Subsequently, the elite engineered lines (A5, and LSG9) were crossed with sweet sorghum (Rio, and R9188). Total sugar contents (over 750 mM), were notably higher in F1, and F2 progenies than the control Rio (480 mM). The sugar contents of the engineered lines (over 750 mM), including T0, T1, F1, and F2, are surprisingly higher than that of the field-grown sugarcane (normal range 600–700 mmol/L). Additionally, analysis of physiological characterization demonstrated that the superior progenies had notably higher rates of photosynthesis, sucrose transportation, and sink strength than the controls.ConclusionsThe genetic engineering approach has dramatically enhanced total sugar content in grain sorghum (T0, and T1) and hybrid sorghum (F1, and F2), demonstrating that sorghum can accumulate as high or higher sugar content than sugarcane. This research illustrates that the SI gene has enormous potential on improvement of sugar content in sorghum, particularly in hybirds and sweet sorghum. The substantial increase on sugar content would lead to significant financial benefits for industrial utilization. This study could have a substantial impact on renewable bioenergy. More importantly, our results demonstrated that the phenotype of high sugar content is inheritable and shed light on improvement for other sugar crops.
Highlights
Sugar content is critically important in determining sugar crop productivity
Isomaltulose was efficiently accumulated in T0 transgenic lines Twenty independent transgenic lines were demonstrated to contain the sucrose isomerase (SI) gene using the polymerase chain reaction (PCR) analysis
Up to 446 mM isomaltulose was accumulated in stalk juice, which was fourfold higher than the total sugar content of the untransformed T×430
Summary
Sugar content is critically important in determining sugar crop productivity. improvement in sugar content has been stagnant among sugar crops for decades. Sweet sorghum has displayed huge potential to be multiple sources of energy, food and animal feed and could be a substitute for sugarcane to produce biofuel [13, 14]. It grows quickly in adverse stress conditions of marginal lands in tropical, subtropical and temperate zones. It is a C4, drought tolerant, high biomass, and high water use efficiency crop that produces stalks up to five meters tall, accumulating sucrose (α-D-glucopyranosyl-1,2-D-fructofuranose). Current sweet sorghum varieties, producing comparatively low sugar content (around 500 mmol/L), urgently require plant breeders to improve sugar accumulation in stalks for biofuel [13]
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