21/10/2024: Camille COSTES' thesis defence

Summary of the thesis:

Sorghum, the world's fifth most important cereal in terms of production, is grown on every continent. In the context of climate change, sorghum is developing rapidly in Europe due to its low input and water requirements. Walls, whose polysaccharides make up the vast majority of dietary fibre, are an important variable to consider when improving the nutritional quality of cereals and processed products derived from grains. Research suggests that endosperm walls may play a key role in the availability and digestibility of these proteins, either by forming a physical barrier or by interacting with the proteins. As a first step, the composition and distribution of parietal polysaccharides were examined in order to better understand the dynamics of wall formation in developing sorghum grains. The polysaccharides of the albumen and outer envelopes of the grains were analysed at different stages of development, using both biochemical and imaging approaches. A transcriptomic analysis was carried out in parallel using albumen and outer envelopes of developing grains, separated by laser microdissection. The aim of this analysis was to identify the genes involved in the biosynthesis and remodelling of cell wall polysaccharides and to monitor their level of expression during grain development.  Taken together, these results provide new information on cell wall formation during sorghum grain development. To assess the impact of cell walls on the digestibility of sorghum proteins, which are known to be less digestible than proteins from other cereals, dry grain albumen cells were isolated by dry fractionation from two genotypes without tannins, but with differences in protein digestibility in the gastrointestinal phase. Cell walls were altered by mechanical grinding or enzymatic treatment to assess the impact of wall integrity on protein digestibility. The state of the walls was examined after fractionation and grinding using biochemical and microscopic analyses. The fractions obtained were characterised in terms of granulometry and sugar and kafirin composition. In vitro protein digestibility was measured to determine the effect of cell wall degradation on this process. This work made it possible to monitor the development and assess the effect of cell wall integrity on grain protein digestibility, and to gather important information for improving grain quality.

Composition of the jury :

    Chairman: Alain Le-Bail, Professor, Oniris Nantes

    Examiners :      

•     Claire Mouquet-River, Research Director: IRD Montpellier
•     Frederic Guedj, Development Manager : Lidea Seeds Mondonville

    Rapporteurs :

•     Myriam Grundy, Research Engineer: INRAE Saint-Gilles
•     Vincent Burlat, Professor: Université Paul Sabatier Toulouse