Wheat represents more than half of the cereal production in France and 92% of this wheat is selected especially for bread-making processes.
Technological quality of wheat is mainly determined by its storage protein content and composition.
Elasticity and suppleness of bread dough enable the dough to rise and are due to the presence of gluten. Gluten is derived from storage proteins in the grain. These proteins represent 80% of wheat proteins. There are 2 main types of storage proteins:
Gliadins: small monomeric proteins that form aggregates, which enable dough extensibility. In Nature, there is an important diversity among the different forms of gliadins.
Glutenins, particularly the ones with high molecular weight, assemble into large polymers, which gives elasticity to dough.
Complementary to storage proteins, other proteins, called puroindolines, present in cell walls of wheat grain, promote the formation of alveoli in bread, thanks to their emulsifying properties. Besides, by playing on wheat grain hardness, they contribute to the formation of flour made up of particles of homogeneous sizes, easier to work with.
Up to now, wheat protein analysis requires a long time and is difficult to set up. Moreover, most of the time, wheat quality for bread making is assessed only at the final stage in the breeding process.
The QualitNblé project has developed new tools to predict the quantity of proteins of technological interest in wheat. These tools, faster and more reliable, can be used directly by seed breeders to develop wheat varieties whose protein types and quality are suitable for applications.
The project’s partners focused on the two main factors determining protein synthesis in wheat: wheat gene pools and farming conditions.
To detect the best gene poolsWithin collections of more than 200 wheat varieties, many variant forms of genes (alleles) coding for different forms of gliadins and glutenins have been identified. Genetic markers that are specific for each allele (SNP, Single Nucleotide Polymorphism) have been developed. These genetic markers have been associated with different phenotypic traits (yield in the field, type and quantity of storage proteins, flour rheology). Hence, thanks to these associations, the markers of alleles related to the best bread-making and agronomic qualities enable breeders to identify, at the earliest stages of plant growth, the best wheat varieties according to the bread-making quality of future grains.
To enhance gene pools by increasing the quantity of proteins of interest
The quantity of synthesized proteins depends on the level of utilization of the corresponding gene by the plant (or level of expression), which is regulated by transcription factors and gene promoters (1). QualitNblé allowed the analysis of allelic variability of genes coding for these transcription factors and for the promoter of genes coding for storage proteins, while associating them with phenotypes. This work allows breeders to have, at the earliest stages of plant growth, markers to select the wheat synthesizing the best storage protein composition for a given application.
Farming conditions play also a role in protein synthesis. It has been shown, in greenhouses, then in fields, that nitrogen and sulphur inputs have an impact on the quantity of synthetized glutenins, as well as on wheat grain hardness, through puroindoline synthesis. This raises questions about the impact of plant nutrition on the regulation of gene transcription. Some genes involved in yield regulation and protein synthesis have been identified, but many studies still have to be done on this topic.
The study of puroindoline synthesis has shown that there is a link between puroindoline synthesis and storage protein synthesis. Thus, the markers developed to assess the quality of gluten protein network could be used, indirectly, to select softer grains. Complementary studies are underway to identify the mechanisms linking these 2 phenomena.
For the first time, QualitNblé has generated tools for the early selection of bread wheat and knowledge necessary for wheat seed producers to further bread wheat improvement using qualitative criteria and set up adapted farming conditions. Several scientific publications and a patent have already highlighted the interest of this very innovative study. Two more patents could be registered.