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beta-Amylase-like proteins function as transcription factors in Arabidopsis, controlling shoot growth and development

Reinhold, H. and Soyk, S. and Simkova, K. and Hostettler, C. and Marafino, J. and Mainiero, S. and Vaughan, Cara K. and Monroe, J.D. and Zeeman, S.C. (2011) beta-Amylase-like proteins function as transcription factors in Arabidopsis, controlling shoot growth and development. Plant Cell 23 (4), pp. 1391-1403. ISSN 1040-4651.

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Plants contain beta-amylase-like proteins (BAMs; enzymes usually associated with starch breakdown) present in the nucleus rather than targeted to the chloroplast. They possess BRASSINAZOLE RESISTANT1 (BZR1)-type DNA binding domains-also found in transcription factors mediating brassinosteroid (BR) responses. The two Arabidopsis thaliana BZR1-BAM proteins (BAM7 and BAM8) bind a cis-regulatory element that both contains a G box and resembles a BR-responsive element. In protoplast transactivation assays, these BZR1-BAMs activate gene expression. Structural modeling suggests that the BAM domain's glucan binding cleft is intact, but the recombinant proteins are at least 1000 times less active than chloroplastic beta-amylases. Deregulation of BZR1-BAMs (the bam7bam8 double mutant and BAM8-overexpressing plants) causes altered leaf growth and development. Of the genes upregulated in plants overexpressing BAM8 and downregulated in bam7bam8 plants, many carry the cis-regulatory element in their promoters. Many genes that respond to BRs are inversely regulated by BZR1-BAMs. We propose a role for BZR1-BAMs in controlling plant growth and development through crosstalk with BR signaling. Furthermore, we speculate that BZR1-BAMs may transmit metabolic signals by binding a ligand in their BAM domain, although diurnal changes in the concentration of maltose, a candidate ligand produced by chloroplastic b-amylases, do not influence their transcription factor function.

Item Type: Article
School or Research Centre: Birkbeck Schools and Research Centres > School of Science > Biological Sciences
Depositing User: Administrator
Date Deposited: 20 Jun 2011 11:09
Last Modified: 17 Apr 2013 12:20

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