The Enzyme-Like Domain of Arabidopsis Nuclear Beta-Amylases is Critical During DNA Sequence Recognition and Transcriptional Activation

Plant BZR1-BAM transcription factors contain a β-amylase (BAM)-like domain, characteristic of proteins involved in starch breakdown. The enzyme-derived domains appear to be non-catalytic, but determine the function of the Arabidopsis thaliana BZR1-BAMs (BAM7 and BAM8) during transcriptional initiation. Microarray experiments with plants overexpressing different mutant versions of the proteins show that only functional BZR1-BAM variants deregulate gene expression and cause leaf developmental abnormalities. Transcriptional changes caused by overexpression of the BZR1 domain alone indicate that the BAM domain increases selectivity for the preferred cis-regulatory element BBRE (BZR1-BAM Responsive Element). In this study, we used the ATH1 GeneChip microarray to investigate transcript abundance in different Arabidopsis thaliana genotypes. Arabidopsis thaliana (accession Columbia) were grown in a nutrient-rich, medium-grade, peat-based compost in Percival AR95 growth chambers (CLF Plant Climatics) at a constant temperature of 20°C, 70% humidity and a 12-h light period with constant, uniform light intensity of 150 μmol•m-2•s-1. Three-week-old plants were harvested 4 h after onset of the light period and immediately frozen in liquid nitrogen. Fourteen individual plants were pooled per replicate.