| dc.description.abstract | Sorghum bicolor is an important lignocellulosic biofuel crop. Its small genome size of ~800 Mbp, reference genome sequence, genetic and genomic resources make it a genetic model for C4 bioenergy grasses. There is a significant natural variation in sugar content in stems of cultivated sorghums. Sweet and biomass sorghums accumulate sugars (mainly sucrose) to 30% of total stem dry weight post-anthesis. These levels rival those of sugarcane but at a fraction of the input as sorghum has low nutritional requirements, high biomass yield, and sustainability features such as drought resistance, high water, and nitrogen use efficiency. The final non-structural carbohydrate content of the stem increases its potential as a biofuel crop.
The analysis of the biochemical and genetic basis of sucrose accumulation in sweet sorghum stems has been a topic of research for more than 20 years. Many gene candidates involved in sugar metabolism, sugar transport, and transcription factors have been analyzed which shed light on the sugar allocation process.
In the present study, genes involved in raffinose family of oligosaccharides (RFOs) metabolism, namely, galactinol synthase (GolS), raffinose synthase (RafS), stachyose synthase (StaS), and alpha-galactosidase (AGA) responsible for the biosynthesis and degradation of RFOs were identified in the sorghum genome. A homology-based approach was used to identify 2 SbGolS, 1 SbRS, 1 SbSTS, and 6 SbAGA genes in the sorghum genome. Transcriptome analyses showed that SbGolS, SbRS, and SbAGA genes exhibited distinct expression profiles in different tissues and developmental stages. The up-regulation of SbRS in the leaves and the up-regulation of SbAGA1 and SbAGA2 genes post-anthesis in stems suggested their potential role in RFO synthesis in leaves and hydrolysis in sweet sorghum stems. This study found that genes involved in RFO hydrolysis are induced in sweet sorghum stems post-anthesis when stems are accumulating high levels of sucrose and starch. This is consistent with the hypothesis that RFO is synthesized in leaves, transported to stems, and subsequently hydrolyzed to release sucrose, thereby contributing to the accumulation of high levels of nonstructural carbohydrates in the stems of some bioenergy sorghum genotypes. | en |
