High conservation among sequences encoding type-V thionins in wheat and Aegilops

Thionins are Cys-rich plant polypeptides of about 5 kD that are synthesized as larger precursors, which include a typical signal peptide and a posttranslationally processed, C-terminal peptide, and are thought to be involved in plant defense (García-Olmedo et al., 1989, 1991, 1992). We have previously reported on a nove1 neutral thionin type in wheat (Triticum aestivum L.), designated type V, which has diverged extensively from type I by a process of acceler- ated evolution specially affecting the mature protein do- main of the precursor (Castagnaro et al., 1992). It was further shown that type-V genes were located within a few kilobases of type-I genes in the long arms of group-1 chro- mosomes in the three genomes (ABD) of allohexaploid wheat and that both types were simultaneously ex- pressed in endosperm (Castagnaro et al., 199