A gibberellin responsive wheat gene has homology to yeast carboxypeptidase Y.

An earlier report (Baulcombe, D. C., and Buffard, D. (1983) Planta 157, 493-501) described the isolation of cDNA clones from mRNAs which are produced in increased amounts when aleurone layers of wheat are treated with gibberellic acid. It is shown here that for one of those cDNAs (2473) the change in level of mRNA in aleurone parallels the change in level of alpha-amylase mRNA. This result was obtained in experiments where the level of gibberellic acid was varied and also when the mRNA was isolated from wheat genotypes which varied in ability to respond to gibberellic acid. In contrast to this, the pattern of 2437 mRNA accumulation in immature grains and in leaf tissue was quite distinct from the pattern of alpha-amylase mRNA accumulation. Analysis of wheat DNA showed that the 2437 mRNA is encoded by a small family of genes located on the short arm of the group 6 chromosomes. One member of this gene family was cloned and sequenced. The coding sequence is interrupted by eight introns and encodes a protein of Mr 55,433. By using hybridization probes from the 5' exon in an S1 nuclease protection assay it was shown that the 2437 mRNA was produced in aleurones (coordinately with alpha-amylase) and in immature grains (not coordinately with alpha-amylase). However, sequence comparison of 1 kilobase of the 5'-flanking region with the sequence of alpha-amylase genes provided no indication of the regulatory elements which would be active in aleurone cells. The protein sequence deduced from the gene sequence has extensive homology with the yeast carboxypeptidase Y, especially in the active site and substrate binding regions. This homology is greater than with the carboxypeptidase I from barley. It is suggested therefore that there are several types of carboxypeptidase encoded in the cereal genome. The sequence of the 2437 protein would represent one of these types and the barley carboxypeptidase I, another.