# Genetic and Environmental Factors Associated to Glutenin Polymer Characteristics of Wheat
## 3 Results and Discussion
### Proteomics Studies Indicate a Possible Stress during Protein Accumulation  
The strong influence of temperature on the polymer characteristics may result from higher activities of the oxidative molecules catalyzing the formation of SS. Among these molecules in the wheat endosperm, we may find the PDI, sulfhydryl oxidases, and reactive oxygen species (ROS), like hydrogen peroxide, dehydroacorbate, and oxidized glutathione. Proteomics analyses of developing wheat endosperm at 21 stages led to the identification of eight PDIs, specifically present in the endoplasmic reticulum, where polymerization occurs: one PDI-2 precursor, three PDIs, and four PDI-likes [31]. Expression of abundance of each of these eight PDIs over the 21 stages (between 0 \({}^{\circ}\)Cd and 1006 \({}^{\circ}\)Cd) were recorded. The curve of the average expression of these eight PDIs clearly shows a decline of the PDIs' abundance after 700 \({}^{\circ}\)Cd (Figure 3). During the 15 last days of grain maturation, the average abundance of PDIs dropped to 55.8%. This decline was recorded for unstressed wheat grown in a controlled environment where air  
Figure 3: Evolution of the average abundance of eight protein disulfide isomerases (PDIs) (\(\pm\) SD) expressed in the endoplasmic reticulum (ER) at 21 stages in developing endosperm (from 0 to 1006 \({}^{\circ}\)Cd) of cultivar “Récital” grown in controlled-temperature environments (computed from [31]). temperature close to the ears did not exceed 24.2 \({}^{\circ}\)C [31], far below the peak temperatures registered over the four years of the experiment. Protein disulfide isomerase (PDI) is a multifunctional redox chaperone of the endoplasmic reticulum (ER) [35]. PDI is a protein folding catalyst and is also responsible for the isomerization, formation, and rearrangement of protein disulfide bonds, thereby providing another mechanism by which native protein conformation is maintained. We may hypothesize that, when temperature increases, the free thiols of glutenins are oxidized until the amount of ROS is not critical. Correct folding and assembly of nascent proteins in ER, aided by chaperones and cochaperones like binding protein (BiP) and PDI, prevents the aggregation of proteins [36]. Accumulation of storage proteins in endosperm creates a heavy load in the secretory pathway and unfavorable environmental conditions, such as heat stress, drought, or pathogen attack, can upset the ER quality control system. When the imbalance between protein load and folding machinery occurs, a stress signal triggers a cellular response, the unfolded protein response (UPR). In wheat stress-related proteins, characteristics of the UPR were found in both soft and hard near-isogenic lines, these stress-related proteins being more abundant in the hard ones [37]. Although no proteomics-transcriptomics studies were carried out over the course of our experiment, the current knowledge strongly supports the idea that higher abnormal polymers result from UPR occurring in wheat endosperm. Higher polymer Mw (up to \(234\times 10^{6}\) Da)--that is, more than 50 times the classic Mw, were recently measured on wheat grown in France where both the high temperature and drought were prevalent [38]. Molecular mechanisms associated with abnormal polymerizations, that are here revealed as resulting from high temperatures, need to be fully analyzed using both transcriptomics and proteomics tools on wheat grown in fully controlled environments. These investigations are obviously needed not only for technological purposes but, also, for human health. When wheat varieties are studied for human health, the amount of insoluble polymers is usually measured by SE-HPLC. This amount, often closely related to the grain PC, gives no measure of polymer Mw. These glutenin polymers are hydrophobic and heat-resistant. Their size is often further increased by oxidation resulting from intense kneading, and they are only partially hydrolyzed during the short fermentations generally practiced today for many baked products.