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 o f 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 i n 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 (AAB B) - T. aestivum (AABBDD) lineage. Alignment of sequences of the section co vering exon4-intron4-exon5 of the various waxy genes led to the identificat ion of gene-specific sequences in intron 4. The sequences specific to the W x-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 observ ation 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 unexpected ly 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 gene tic mechanism explaining these observations is discussed.