Identification of several new classes of low-molecular-weight wheat gliadin-related proteins and genes

During the initial phases of a wheat endosperm Expressed-Sequence-Tag (EST) project, several clones were determined to be related to wheat gliadin seq uences, but not similar enough to be classified into any of the traditional gliadin families [alpha-, gamma-, and omega -gliadins, low-molecular-weigh t (LMW) glutenins]. Complete sequences of these cDNA clones revealed four n ew classes of gliadin-related endosperm proteins, but lacking a prominent r epeat domain which until now has been characteristic of the gliadins. Two o f these classes are related to different minimally described groups of Trit iceae endosperm proteins. One class of proteins, which has N-terminal amino -acid sequences matching members of a reported 25-kDa globulin family from wheat, is shown by amino-acid sequencing to match to a family of 25-kDa end osperm proteins, is encoded by a multigene family, and is most similar to t he LMW-glutenins. A second new class shows N-terminal homologies to LMW sec alins from rye, and has an amino-acid composition similar to wheat and barl ey LMW proteins with extraction properties similar to prolamins. The third class is most similar to a-gliadins, and the fourth class has no close asso ciation to previously described wheat endosperm proteins.