Differential regulation of the barley (Hordeum vulgare) transcripts B22E and B12D in mature aleurone layers

Abstract

Previously, B12D and B22E have been characterized as Barley aleurone and embryo (Balem) transcripts, expressed during seed maturation and embryo germination. The open reading frame of B12D cDNAs encodes a protein of unknown function highly conserved in mono-and dicotyledonous species, while B22E encodes a metallothionein-like protein. Several slightly different B22E transcripts have earlier been identified. Our objective was to investigate the number of B12D genes, and B12D and B22E expression patterns in mature aleurone. Gnomic Southern hybridization and primer extension experiments suggest the presence of a B12D gene family in barley with at least 8 or 9 members. B12D transcripts can also be identified in the starchy endosperm, and a primer extension analysis indicates that some of these genes are expressed in the starchy endosperm 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 promoter-GUS construct to be transcriptionally active. The HvR12Dg1 promoter 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. However, both transcripts are up-regulated by the presence of the germinating embryo. For B22E this effect is not mimicked by applying GA(3) exogenously 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 induced in the aleurone during germination.