Stem vacuole-targetted sucrose isomerase enhances sugar content in sorghum

Abstract

Background Sugar 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). Results The 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. Conclusions The 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.

Physiological and biochemical processes underlying the differential sucrose yield and biomass production in sugarcane varieties

“…As stalk SAI activity provides substrates for supporting the growth of immature and expanding tissues in sugarcane (Rossouw et al., 2007), a greater capacity for sucrose accumulation at maturation is expected in varieties presenting high SAI activity, as IACSP94-2094. In addition, increased SAI activity may contribute to the remobilisation of sucrose stored in vacuoles (Liu et al., 2021).…”

Enhancement of healthful novel sugar contents in genetically engineered sugarcane juice integrated with molecularly characterized ThSyGII (CEMB-SIG2)

“…An efficient catalytic performance indicating immediate remarkable TH assembly was observed before its deliverance to belligerent vacuole. Hence plants are unable to metabolize SUC isomers 24 . Achieving triggered yield and purified TH containing valued compound required optimizing mechanism of developmental gene expression, stability related to TH synthase in localized vacuoles so that increased TH contents might be progressive to harvested sugarcane stalks.…”