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The NitroSorg project is funded by CASDAR, Ministère de l'Agriculture et de l'Alimentation, France. It involves INRAE and CIRAD through the participation of the AGAP, IATE, BOA research units and the PEAT Experimental Unit, the Eurosorgho and RAGT2n seed companies, and the technical institute ITAVI. Although the SELMET research unit does not benefit directly of financial support of the project, it provides its expertise on feed quality phenotyping tools to the consortium. Nitrosorg will begin in 2022 and will last 42 months. It brings together a multidisciplinary consortium of biologists, geneticists, breeders, biochemists and poultry feed specialists to better understand the establishment of sorghum grain quality for poultry feeding and contribute to the development of breeding tools to optimize breeding efficiency for this target. Indeed, the low digestibility of sorghum grain proteins by gastrointestinal proteases, which has the particularity of decreasing even further after cooking, represents an important obstacle to a wider use of sorghum for feed but also for human nutrition. This low digestibility can be attributed to the interaction of proteins with other grain compounds such as starch or tannins, but is mainly related to the structure and properties of the storage proteins of sorghum grain (kafirins). One of the objectives of this project is to develop high-throughput characterization tools for the protein content and digestibility, but also starch and tannin content and endosperm texture that can affect this digestibility. The consortium will mobilize these tools to characterize the current European varietal offer, a panel representing the worldwide diversity, and the parental lines of the partner's breeding programs. Finally, we will carry, on a smaller panel of genotypes, an analysis of kafirin composition, and an exhaustive analysis of in vitro and in vivo protein digestibility (as part of poultry feeding). These analyses should allow us to assess the relevance of the high-throughput screening tools developed and will lead to the definition of the target ideotypes for poultry feeding. In the long term, these results will contribute to the development of grain sorghum varieties with a better protein content and digestibility, and therefore an improved nutritional value.

International audience; Most sorghum biomass accumulates in stem secondary cell walls (SCW). As sorghum stems are used as raw materials for various purposes such as feed, energy and fiber reinforced polymers, identifying the genes responsible for SCW establishment is highly important. Taking advantage of studies performed in model species, most of the structural genes contributing at the molecular level to the SCW biosynthesis in sorghum have been proposed while their regulatory factors have mostly not been determined. Validation of the role of several MYB and NAC transcription factors in SCW regulation in Arabidopsis and a few other species has been provided. In this study, we contributed to the recent efforts made in grasses to uncover the mechanisms underlying SCW establishment. We reported updated phylogenies of NAC and MYB in 9 different species and exploited findings from other species to highlight candidate regulators of SCW in sorghum. We acquired expression data during sorghum internode development and used co-expression analyses to determine groups of co-expressed genes that are likely to be involved in SCW establishment. We were able to identify two groups of co-expressed genes presenting multiple evidences of involvement in SCW building. Gene enrichment analysis of MYB and NAC genes provided evidence that while NAC SECONDARY WALL THICKENING PROMOTING FACTOR NST genes and SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN gene functions appear to be conserved in sorghum, NAC master regulators of SCW in sorghum may not be as tissue compartmentalized as in Arabidopsis. We showed that for every homolog of the key SCW MYB in Arabidopsis, a similar role is expected for sorghum. In addition, we unveiled sorghum MYB and NAC that have not been identified to date as being involved in cell wall regulation. Although specific validation of the MYB and NAC genes uncovered in this study is needed, we provide a network of sorghum genes involved in SCW both at the structural and regulatory levels.

Sweet and biomass sorghum are expected to contribute increasingly to bioenergy production. Better understanding the impacts of the genotypic and environmental variabilities on biomass component traits and their properties is essential to optimize energy yields. This study aimed to evaluate whether traits contributing to stem biomass growth and biochemical composition at different biological scales (co)vary with the genotype and the water status in sorghum. Height genotypes were studied over two years in field conditions in southern France under two water treatments (well watered vs. 25 days' dry down during stem elongation). Main stem internode number, size, (non)structural carbohydrate, and lignin contents were measured at the end of the stress period and/or at final harvest, together with biochemical and histological analyses of the youngest expanded internode. The tallest genotypes showed the highest stem dry weights and lignin contents. Stem (structural) biomass density was positively correlated with lignin content, particularly in internode parenchyma. Stem soluble sugar and lignin contents were inversely proportional across genotypes and water conditions. Genotypes contrasted for drought sensitivity and recovery capacity of stem growth and biochemical composition. The length and cell wall deposition of internodes expanding under water deficit were reduced and did not recover, these responses being weakly correlated. Genotypic variability was pointed out in the growth recovery of internodes expanding under re-watered conditions. According to the observed genotypic variability and the absence of antagonistic correlations between the responses of the different traits to water availability, it is suggested that biomass sorghum varieties optimizing their responses to water availability in terms of growth and cell wall deposition can be developed for different bioenergy targets.

International audience; Polymer composites prepared with a polymer matrix reinforced by elongated, broken fragments of plant stems can in some cases favorably compete with the same composite reinforced by glass fibers. However, the mechanical properties of the final composite are directly related to the properties of the stem fragments. Cellulose is the main polymer controlling the mechanical strength of these fragments. Two plants will be studied, miscanthus and sorghum. We will show that amount of cellulose in the stem fragments depends on the preparation methods of these fragments. We will report the correlations which exists between the amount of cellulose and its location within the different tissues of the stem and the mechanical properties of the final composite product.

International audience; Composites prepared with whole sorghum stem fragments reinforcing a polyethylene matrix were studied using ten different sorghum genotypes. We first built of a robust protocol ensuring an accurate assessment of composite physical and mechanical properties. It shows that for a given sorghum genotype, the composition of the stem fragments is depending on the size of the fragments. This justifies the need to use a similar stem fragment size for comparing genotypes. During compounding and injection, fragments are broken, to an extend which depends on genotypes. This robust processing protocol shows that there are large differences in the final mechanical properties of the composites depending on the genotype. This is correlated with the histological structure and the biochemical composition of each genotype, showing correlations between the amount of cellulose, hemicellulose and lignin present in the stem fragments with the mechanical properties of the composites, as well as the importance of the location of cellulose (sclerenchym fibers versus parenchym tissues and vessels). We will show the difficulties of working with small, well identified amounts of biological materials when dealing with composite-filler biochemical and structural characteristics which are heavily varying between on position to another along the plant stem. This work is the first step of a plant breeding process for identifying the best sorghum varieties to be used for preparing polymer composites.

The development of multi-purpose sorghum varieties suitable not only for food, but also for feed and other applications became a priority for most of the breeding programs. However, a better understanding of the genetic determinism of stover quality is required. A BCNAM design involving 3 recurrent parents (RP) and 29 donor parents (DP) has been developed in order to provide the sorghum community with a high resolution mapping design and a relevant breeding scheme towards the development of varieties suitable for the soudano sahelian region. The aim of this study was to characterize the parental lines of a BCNAM multiparental design for their main stem composition and histological properties in order to: • Assess the relevance of this genetic design to reach a better understanding of the genetic bases of these traits • Evaluate the effect of the sowing dates, and height diversity on the biochemical composition of the stems • Have a first image of the relationships between stem histological and biochemical traits

In addition to being the fifth cereal in terms of grain production, the interest of sorghum as a feed and energy crop is increasingly underlined. Selection of sorghum genotypes for fodder and energy production relies on an in-depth understanding of stem tissue organization and cell wall characteristics variability. Although histological analyses of two genotypes harboring contrasting stem diameter revealed similar tissue organizations and cell sizes, their kinetics of biomass degradation when treated with enzymatic cocktails were different, the largest stem diameter genotype presenting a faster degradation with a lower percentage of monosaccharide solubilised, suggesting differences in soluble sugar content and cell wall polymer content and accessibility. According to these results we then focus our attention on the cell wall composition. From a previous characterization of 410 sorghum accessions using near infrared reflectance spectroscopy, a panel of 13 genotypes maximizing the diversity of cell wall properties were subjected to FTIR analyses, klason lignin and p-hydroxycinnamic acids contents measurement, and determination of lignin monomeric composition. In parallel, saccharification efficiency of the cell walls was evaluated. These analyses revealed a significant genetic variability of cell wall saccharification yield which has been associated with the variability of the lignin content in the cell wall, the S monomers content in the uncondensed lignin part and the concentration in esterified p-coumaric acid. Finally, addition of an Alkali pre-treatment before the enzymatic treatment showed significant improvement of cell wall saccharification yield but contrasting responses of the genotypes analyzed in terms of final yield and degree of improvement.

In addition to being the fifth cereal in terms of grain production, the interest of sorghum as a feed and energy crop is increasingly underlined. Selection of sorghum genotypes for fodder and energy production relies on an in-depth understanding of stem tissue organization and cell wall characteristics variability. Although histological analyses of two genotypes harboring contrasting stem diameter revealed similar tissue organizations and cell sizes, their kinetics of biomass degradation when treated with enzymatic cocktails were different, the largest stem diameter genotype presenting a faster degradation with a lower percentage of monosaccharide solubilised, suggesting differences in soluble sugar content and cell wall polymer content and accessibility. According to these results we then focus our attention on the cell wall composition. From a previous characterization of 410 sorghum accessions using near infrared reflectance spectroscopy, a panel of 13 genotypes maximizing the diversity of cell wall properties were subjected to FTIR analyses, klason lignin and p-hydroxycinnamic acids contents measurement, and determination of lignin monomeric composition. In parallel, saccharification efficiency of the cell walls was evaluated. These analyses revealed a significant genetic variability of cell wall saccharification yield which has been associated with the variability of the lignin content in the cell wall, the S monomers content in the uncondensed lignin part and the concentration in esterified p-coumaric acid. Finally, addition of an Alkali pre-treatment before the enzymatic treatment showed significant improvement of cell wall saccharification yield but contrasting responses of the genotypes analyzed in terms of final yield and degree of improvement.