DIFFERENTIAL REGULATION OF THE BARLEY (HORDEUM-VULGARE) TRANSCRIPTS B22E AND B12D IN MATURE ALEURONE LAYERS

Previously, B12D and B22E have been characterized as Barley aleurone a nd embryo (Balem) transcripts, expressed during seed maturation and em bryo germination. The open reading frame of B12D cDNAs encodes a prote in of unknown function highly conserved in mono-and dicotyledonous spe cies, while B22E encodes a metallothionein-like protein. Several sligh tly different B22E transcripts have earlier been identified. Our objec tive was to investigate the number of B12D genes, and B12D and B22E ex pression patterns in mature aleurone. Gnomic Southern hybridization an d primer extension experiments suggest the presence of a B12D gene fam ily in barley with at least 8 or 9 members. B12D transcripts can also be identified in the starchy endosperm, and a primer extension analysi s indicates that some of these genes are expressed in the starchy endo sperm only. A number of genes appear to be transcribed in all tissues investigated; starchy endosperm, pericarp, immature and mature embryos and aleurone, and mature aleurone incubated with GA(3). One B12D gene , HvB12Dg1, was isolated and shown by particle bombardment with a prom oter-GUS construct to be transcriptionally active. The HvR12Dg1 promot er contains elements similar to those of the gibberellic acid response complex (GARC). B12D transcripts are found in the aleurone of imbibed embryoless grains, while B22E transcripts are barely detectable. Howe ver, both transcripts are up-regulated by the presence of the germinat ing embryo. For B22E this effect is not mimicked by applying GA(3) exo genously to imbibed embryoless grains, while the B12D transcript level increases 2- to 3-fold, at most. On the other hand, ABA can suppress B12D expression. Our investigations indicate that gibberellic acid may not be directly involved in the up-regulation of all transcripts indu ced in the aleurone during germination.