Analysis of polysaccharide composition during sorghum grain development

International audience Sorghum (Sorghum bicolor (L.) is the fifth most important grain produced in the world. Native to Africa,sorghum is now cultivated all over the world. In a context of climate change, its cultivation is increasing inEurope due to its low input and water requirements. The attractiveness of sorghum grain is also explainedby its nutritional qualities, in particular its gluten-free and relatively high content of polysaccharides andproteins.In sorghum grains, polysaccharides are of two types: storage and parietal polysaccharides. Storagepolysaccharides are composed of starch (60-75% of grain) accumulated in the endosperm. Cell wallpolysaccharides, representing 2 to 7 % of grain weight, are mainly arabinoxylans and mixed β-glucans.Beside their structural role, cell wall polysaccharides impact the nutritional and technological qualities ofgrains as they represent the vast majority of dietary fibers.While the composition of cell walls in mature grains has been well studied, less is known about thepolysaccharide deposition during grain development and the mechanisms that drive their assembly withinthe cell wall, even though they are key factors in determining the physico-chemical properties of cell wallsand the end use of grain.In this purpose, polysaccharides in the endosperm and outer layers of grains were analyzed at differentstages of grain development. Mixed β-glucan and starch contents were also determined. By specificstainings and immunolabellings, polysaccharides were monitored in the different tissue layers. To go further,transcriptomic analyses were carried out after laser microdissection of grains to separate endosperm fromouter layers. This analysis led to the determination of genes involved in the biosynthesis and remodellingof cell wall polysaccharides.These overall results provide new knowledges on polysaccharide assembly during the development ofsorghum grain