New molecular targets to improve maize seed value

Context

In Europe, breakfast cereals represent a market worth €6 billion. Cornflakes are made from maize imported from South America. To increase its competitiveness, the European maize industry wants to develop hybrids that combine good agronomic yields with textural qualities suited to the cornflake process. The glassy fraction resulting from the fractionation of grains (hominies) is the only one used to make cornflakes. In this context, research has been undertaken to determine the molecular and physicochemical bases of the formation of the vitreous texture of the grain in order to optimise varietal selection for hominy yield. This work was carried out as part of a collaboration supported by the Fond Unique Interministériel (FUI GranoFlakes coordinated by the Céréales Vallée competitiveness cluster) involving industrial partners, a seed company (Limagrain), a specialist in cooking-extrusion (Clextral), an SME specialising in image analysis (Veodis 3D) and two laboratories in the CEPIA department (UR-BIA in Nantes and UMR IATE in Montpellier).

Results

By analysing different genotypes, horny and dentate, we have demonstrated a close relationship between vitrosity and the distribution and composition of lipids in the albumen (the compartment that accumulates starch and grain reserve proteins). In particular, a phospholipid trapped within the starch, lysophosphatidylcholine (lysoPC), is in higher concentration in the vitreous fraction than in the floury fraction of the albumen. The same is true for the amylose content, which is one of the main components of starch, suggesting that amylose-lysoPC complexes could play a major role in the construction of vitrosity. At the same time, the structure of the starch was modified, revealing numerous protein channels in the glassy fraction. The origin of this lipid, lysoPC, is still unknown, but its content is closely associated with that of its precursor phosphatidylcholine, a major component of the membranes of the endoplasmic reticulum where the synthesis of reserve proteins takes place. This protein synthesis is particularly intense in the vitreous part of the albumen. It therefore appears that lipids, which are minor compounds (<1% of albumen), are excellent markers of the construction of vitrosity and of the complex metabolic processes controlling the accumulation of protein and starch reserves.

Outlook

A transcriptomic analysis is underway to identify, during grain development, the genes associated with lipid homeostasis and in particular those responsible for the accumulation of lipids trapped within starch. Analysis of the gene networks involved in the synthesis of lipids, reserve proteins and starch should make it possible to develop new genetic tools for selecting maize suitable for semolina technology.

Looking beyond maize, this study opens up new prospects for tackling the role of starch-complexed lipids in the assembly of its polysaccharide components and the interactions between proteins and starch within the albumen of cereals.

Partnership

This work is being carried out by Mathieu Gayral (BIA-ELIPS doctoral student) as part of the GranoFlakes FUI project (Céréales Vallée cluster) involving private partners (Limagrain, Clextral, Veodis 3D) and INRA (the BIA unit in Nantes and the IATE unit in Montpellier).