Raffinose oligosaccharides support sorghum productivity and resilience

Understanding how plants produce and move sugars could lead to more robust energy crops.

The Science    

Raffinose family oligosaccharides (RFOs) are sugars that store energy and help plants withstand stresses like drought, heat, and cold. RFOs also help transport sugars in several species. For this study, researchers identified the sorghum genes responsible for making and breaking down RFOs and analyzed their activities in different leaf and stem cell types. The results indicate RFOs are produced in leaf cells responsible for photosynthesis and broken down in veins, releasing sucrose where it can be transported throughout the plant. This suggests that RFOs improve sucrose distribution by enhancing short-distance movement within organs.  

The Impact

Plans to slow climate change call for increased use of plant-based fuels and chemicals to replace fossil fuels and petrochemicals. Energy sorghum is a promising source of low carbon-intensity products that can grow on marginal crop lands with little water or fertilizer, producing a lot of biomass while using its deep roots to store carbon in the soil. Understanding the mechanisms that control RFOs helps explain the plant’s productivity and how it redistributes and stores energy-rich sugars. That could enable scientists to engineer more robust crops that can withstand drought and other stressors made worse by climate change and pack more easily fermentable sugars into the stem.

Summary

In this study, researchers with the Great Lakes Bioenergy Research Center examined the expression of the sorghum RFO pathway genes in leaves, stems, and roots of three varieties of sorghum during plant growth and development.

They found that certain genes involved in RFO biosynthesis had peak expression early in the morning in leaves, with a higher overall expression in leaves than in stems and roots. They also found that genes that synthesize RFOs from sucrose and galactose were expressed in photosynthetically active leaf mesophyll cells, while genes responsible for RFO hydrolysis were expressed in leaf vascular cells surrounding the phloem where release of sucrose could enhance sucrose transport from leaves to other parts of the plant. In stems, genes involved in RFO hydrolysis were expressed at high levels in pith parenchyma cells that store sucrose implicating a role for RFO-mediated sucrose redistribution in stem sucrose storage.  

Contact

John Mullet
Texas A&M University
john.mullet@ag.tamu.edu