BARLEY EMBRYO GLOBULIN-1 GENE, BEG1 - CHARACTERIZATION OF CDNA, CHROMOSOME MAPPING AND REGULATION OF EXPRESSION

We report identification of a 2189 bp cDNA clone from barley correspon ding to a single-copy gene, Beg1 (Barley embryo globulin), on chromoso me 4, which encodes a storage globulin. In barley, the major protein r eserve in the aleurone layer belongs to the 7S globulin class of prote ins found in many seeds. Electrophoretically and antigenically similar proteins are present in the barley embryo. Accumulation of Beg1 mRNA was noted beginning 15-20 days post-anthesis in both the aleurone laye r and embryo of the developing barley grain but. not in the starchy en dosperm. A high level of Beg1 mRNA is also present in the mature imbib ed aleurones, which can be repressed by treatment with gibberellic aci d. This repressive effect of gibberellin on the levels of Beg1 mRNA is confirmed in the gibberellin response-constitutive mutant, slender, w hose aleurone layers do not accumulate Beg1 mRNA even in the absence o f applied gibberellic acid. The deduced primary translation product of the Beg1 mRNA is a 637 amino acid (72 kDa) protein with homology to m aize embryo globulin 1 (GLB1) and a partial sequence of a wheat 7S glo bulin. The internal amino acid sequence of BEG1 closely matches the N- terminal sequence of isolated barley aleurone globulin. Seven imperfec t tandem repeats of 16 amino acids each are present near the N-terminu s of BEG1, which conform to the consensus HGEGEREEEXGRGRGR, and contri bute to the observed unusual amino acid composition of this protein. A second, distinct barley globulin gene, Beg2, which is homologous to m aize Glb2, was detected by Northern and Southern analysis. Beg2 and Be g1 are regulated differently which may indicate variation in storage o r utilization properties among the barley globulins.