The α-gliadin genes from Brachypodium distachyon L. provide evidence for a significant gap in the current genome assembly.

Brachypodium distachyon, is a new model plant for most cereal crops while gliadin is a class of wheat storage proteins related with wheat quality attributes. In the published B. distachyon genome sequence databases, no gliadin gene is found. In the current study, a number of gliadin genes in B. distachyon were isolated, which is contradictory to the results of genome sequencing projects. In our study, the B. distachyon seeds were found to have no gliadin protein expression by gel electrophoresis, reversed-phase high-performance liquid chromatography and Western blotting analysis. However, Southern blotting revealed a presence of more than ten copies of α-gliadin coding genes in B. distachyon. By means of AS-PCR amplification, four novel full-ORF α-gliadin genes, and 26 pseudogenes with at least one stop codon as well as their promoter regions were cloned and sequenced from different Brachypodium accessions. Sequence analysis revealed a few of single-nucleotide polymorphisms among these genes. Most pseudogenes were resulted from a C to T change, leading to the generation of TAG or TAA in-frame stop codon. To compare both the full-ORFs and the pseudogenes among Triticum and Triticum-related species, their structural characteristics were analyzed. Based on the four T cell stimulatory toxic epitopes and two ployglutamine domains, Aegilops, Triticum, and Brachypodium species were found to be more closely related. The phylogenetic analysis further revealed that B. distachyon was more closely related to Aegilops tauschii, Aegilops umbellulata, and the A or D genome of Triticum aestivum. The α-gliadin genes were able to express successfully in E. coli using the functional T7 promoter. The relative and absolute quantification of the transcripts of α-gliadin genes in wheat was much higher than that in B. distachyon. The abundant pseudogenes may affect the transcriptional and/or posttranscriptional level of the α-gliadin in B. distachyon.