Stem wax holds clues to sorghum resilience

Three black and white panels showing scanning electron microsopic images of stem wax
Scanning electron microscopy images show early stem wax deposition (left), late wax deposition (center), and the elongated tubules and thicker wax plate as the plant matures and wax is exposed to the outside environment. Images courtesy of authors. Photo courtesy of the authors.

Understanding mechanisms that regulate wax production could enable scientists to engineer plants to better withstand drought, heat, and pests. 

The Science    

The cuticle is a protective covering that helps plants reduce water loss and shields them from harmful sun rays, diseases, and insects. The cuticle is composed of cutin, a natural polyester sheet, and an outermost epicuticular wax layer. Epicuticular wax can form plates, crystals, rods, needles, and tubules, and the composition and thickness varies by species, parts of the plant, and environmental conditions. In this study, scientists analyzed the high epicuticular wax loads that build up on sorghum stems and the genetic mechanisms that govern them in order to better understand how wax helps the plant withstand environmental stressors like heat and drought. 

The Impact

Plans to slow climate change call for increased use of sustainable plant-based fuels and chemicals to replace fossil fuels and petrochemicals. With deep roots that add carbon to the soil, bioenergy sorghum is a promising source of these biofuels and products. It can grow on marginal farmland with little water or fertilizer, producing a lot of biomass without competing with food crops. Understanding epicuticular wax production and identifying the genes that regulate wax loads and composition could enable scientists to engineer more resilient bioenergy crops that produce more wax, which could be stripped off and used to make biofuels, food additives, and industrial products, improving the economics of biofuel production.

Summary

Scientists with the Great Lakes Bioenergy Research Center sought to characterize the accumulation, composition, form, and timing of stem wax loads as well as the wax pathway gene expression and regulation. Wax loads on sorghum were much higher than stem and leaf loads on the genetic model arabidopsis and crops such as rice and corn. Scanning electron microscopy showed minimal wax on very young stem internodes prior to the onset of elongation and that wax tubules first appear when internode cell elongation is complete. During early stages of stem development, the wax consists mostly of long-chain wax alcohols. Wax on fully developed stems is primarily composed of long chain (C28/30) aldehydes.

Additionally, researchers found expression of genes involved in wax biosynthesis was low in immature stem segments but increased shortly after internode elongation and remained on for the duration of vegetative growth. Gene regulatory network analysis identified a suite of transcription factors that are predicted to modulate the composition and amount of wax accumulation on bioenergy sorghum stems.

Contact

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

Research Theme
Sustainable Bioenergy Cropping Systems
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