Comparative Expression Profile of Genes Encoding Intolerant Proteins in Bread vs. Durum Wheat During Grain Development

Wheat is the major cereal crop in the world. While wheat proteins provide the nutritional requirement for humans, the major concern associated with them is their intolerance among a large genetically predisposed population. These proteins include gluten, albumins like amylase/trypsin inhibitors (ATIs), serpins, thionins, and defensins. In this study, we performed a comparative (bread vs. durum wheat) expression analysis of the genes encoding for different intolerant proteins (IP) during grain development, through transcriptomics approach. Two libraries were generated from each genotype with an average of 103.81 million reads, resulting in 121.3K transcripts for bread wheat; and 75.20 million reads resulting in 117.7K transcripts for durum wheat. RNA-seq results were validated through qRT-PCR. All transcripts related to IPs were extracted; 146 and 133 transcripts were identified in case of bread and durum wheat, respectively. However, only five IP genes were differentially expressed (DEGslog2fold>2) and all of them were classified under the GO terms 'Molecular Function'. For comparative expression of the IP genes between the two genotypes, fragments per kilobase of exon model per million reads mapped (FPKM) values of each gene were studied. None of the IP transcripts were falling in any pathway, that is because these IPs are synthesized from the genes through transcription followed by translation. These IPs, during grain development, belonged to the major categories of thionin, serpin, ATI, gliadin and glutenin. Bread wheat was expressing a greater number of IP genes and mostly they were upregulated in comparison to the durum wheat. Highest numbers of IP transcripts were mapped on the BB genome; and maximum IP genes were located in chromosome1D. IP genes with higher expression in both the genotypes were further analysed for their stage-specific expression during grain development. Thionins, gliadins and glutenins were mainly expressed at 4-5 weeks after anthesis (WAA); whereas, serpins and ATIs were expressed at 3-4 WAA. The expression of thionin and serpin genes was comparatively low throughout the grain development process, when compared to other IPs. We have also analysed the transcripts related to amylose and amylopectin biosynthesis, where durum wheat showed a high amylose: amylopectin ratio in comparison to bread wheat. Our study through transcriptome analysis is another support for the hypothesis that tetraploid durum wheat is less intolerant and better for consumption for the vulnerable population than that of hexaploid bread wheat.

Automated summary

In this study, a comparative analysis of the genes encoding different intolerant proteins (IP) in bread and durum wheat was performed using a transcriptomics approach. The results showed that bread wheat expressed a greater number of IP genes, most of which were upregulated. These IP genes belonged to thionin, serpin, ATI, gliadin, and glutenin categories. Durum wheat showed a higher amylose:amylopectin ratio compared to bread wheat. These findings support the hypothesis that tetraploid durum wheat is less intolerant and more suitable for consumption by the vulnerable population than hexaploid bread wheat.