Biochemical data bearing on the origin of the B genome in the polyploid wheats

Abstract

For many years each of the species Aegilops bicornis, Aegilops longissima, Aegilops searsii, Aegilops sharonensis, Aegilops speltoides, and Triticum urartu has been implicated as the donor of the B genome in the polyploid wheats. Biochemical and cytological data have revealed that T. urartu possesses a genome similar to that of T. monococcum, and therefore it may be the source of the A genome in T. turgidum and T. aestivum. This revelation therefore excludes T. urartu from the list of putative B-genome donors. To determine which of the remaining species is the source of the B chromosome set, the amino acid sequences of their purothionins were compared with that of the α1 purothionin coded for by the Pur-1B gene on chromosome 1 in the B genome of T. turgidum and T. aestivum. The residue sequences of this protein from Ae. bicornis, Ae. longissima, Ae. searsii, Ae. sharonensis, and Ae. speltoides differed by 1, 6, 1, 1, and 2 amino acid substitutions, respectively, from the α1 protein. These results suggest that either Ae. bicornis, Ae. searsii, or Ae. sharonensis was the most likely donor of the B genome. If the B genome in the polyploid wheats is monophyletic in origin, the collective findings of this and other investigations indicate that Ae. searsii is the most likely donor. The possibility that the B genome in the polyploid wheats could have a polyphyletic origin is also discussed.Key words: polyploid wheats, putative B-genome donors, purothionins, monophyletic, polyphyletic.