Sharp divergence between wheat and barley at loci encoding novel members of the trypsin/α-amylase inhibitors family

Amino acid sequences for three members (CMxl, CMx2, and CMx3) of a new subfamily of trypsin/Ol­ amylase inhibitors in wheat have been deduced from the nucleotide sequences of the corresponding cDNAs. A cDNA clone encoding CMx l was selected from a wheat developing endosperm library using a probe that encoded barley trypsin inhibitor BTI-CMe at low stringency. Sequences corresponding to CMx2 and CMx3 were obtained from cDNA amplified by the polymerase chain reaction. The three CMx sequences contain a premature stop codon after 363 nt, as well as a second stop codon at the same position as in BTI-CMe (nt 439-441). Southern analysis of DNAs from diploid, tetraploid, and hexap­ loid wheats, as well as from aneuploid lines, indicate that there is a single CMx locus in each of the three genomes of hexaploid wheat, respectively associated with chromosomal arms 4AS, 4BS, and 4DL. These genes are expressed early during endosperm development and not expressed at detectable levels in other tissues. Evolutionary implications are discussed.