Characterization of waxy proteins and waxy genes of Triticum timopheevii and T-zhukovskyi and implications for evolution of wheat

The granule-bound starch (GBSS I, waxy protein) in Triticum timopheevii (A(t)A(t)GG) and T. zhukovskyi (A(t)A(t)A(z)A(z)GG) and a diagnostic section of the genes encoding GBSS-I from the Wx-TtA and Wx-G loci of T. timopheevii and the Wx-TtA, Wx-G, and Wx-TzA loci of T. zhukovskyi were investigated in this study. The waxy proteins in these two polyploid wheats could not be separated into distinct bands, in contrast to those in the T. turgidum (AABB) - T. aestivum (AABBDD) lineage. Alignment of sequences of the section covering exon4-intron4-exon5 of the various waxy genes led to the identification of gene-specific sequences in intron 4. The sequences specific to the Wx-TtA and Wx-G genes of T. timopheevii were different from those of the Wx-A1 gene and Wx-B1 genes of T. turgidum and T. aestivum. A surprising observation was that the Wx-TzA of T. zhukovskyi did not match with the Wx-TmA of T. monococcum, a putative donor of the A(z) genome, but matched unexpectedly and perfectly with the Wx-B1 gene on chromosome 4A, which is proposed to have translocated from the chromosome 7B of T. aestivum. The possible genetic mechanism explaining these observations is discussed.