Hormonal and developmental control of gene expression in wheat

It is likely in plants, as in animal and fungal cells, that development involves the coordinated regulation of sets of genes. It is further likely that when this regulation acts on transcription that the coordination is mediated via trans-acting factors that recognize regulatory elements close to the responsive genes. In wheat (and barley) aleurone cells, a set of genes including those for a-amylase and for other hydrolases show increased expression at the RNA and transcriptional level in response to gibberellic acid. Based on the pattern of expression in various experimental conditions it seems likely that they are a co-regulated set, in the sense described above. However, a comparative analysis of 5' flanking regions has been made and, after the influence of relatedness between different members of gene families is accounted for, no sequence motifs can be identified that could be regulatory elements. More direct methods of analysis for such elements are described involving analysis of expression from natural or artifically constructed sequence variants. There is a second aspect to the regulated expression of aleurone genes when they are expressed non-coordinately and not under the control of gibberellic acid in non-aleurone tissues. In some instances this is because the same gene, expressed from the same promoter, is expressed in the different tissues and suggests that there are multiple regulatory elements close to these genes that respond to different stimuli depending on the stage of development. The a-Amy2 and carboxypeptidase genes of wheat use this strategy. In other instances, however, it can be seen that the dual mode of expression is achieved when multigene families have evolved in which different subsets have a different capability of expression. This strategy is exemplified by the a -Amy1 and a -Amy3 subsets of the a-amylase gene families