Similarities of omega gliadins from Triticum urartu to those encoded on chromosome 1A of hexaploid wheat and evidence for their post-translational processing

The ω-gliadins encoded on chromosome 1 of the A genome were purified from Triticum aestivum L. (2n=6x=42, AABBDD) cv. Butte86, nullisomic 1D-tetrasomic 1A of cv. Chinese Spring (CS N1DT1A), and the diploid T. urartu (2n=2x=14, AA). Reverse-phase high-performance liquid chromatography combined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis of gliadin extracts from CS nullisomic-tetrasomic (NT) lines confirmed the assignment to chromosome 1A. The purified ω-gliadins were characterized by mass spectrometry and N-terminal sequencing. The 1A-encoded ω-gliadins were smaller than 1B- or 1D-encoded ω-gliadins. The N-terminal amino acid sequences for 1A ω-gliadin mature peptides were nearly identical to those for the T. urartu ω-gliadins and were more similar to 1D ω-gliadin sequences than to sequences for T. monococum ω-gliadins, barley C-hordeins, or rye ω-secalins. They diverged greatly from the N-terminal sequences for the 1B ω-gliadins. The data suggest that T. urartu is the A-genome donor, and that post-translational cleavage by an asparaginyl endoprotease produces those ω-gliadins with N-terminal sequences beginning with KEL.