Disease relevance of BMY2

• Expression of the ct-Bmy cDNA in E. coli confirmed that the encoded protein possesses beta-amylase activity [1].
• Cloning of the beta-amylase gene from Bacillus cereus and characteristics of the primary structure of the enzyme [2].

High impact information on BMY2

• Repression of the activity of a plastidic beta-amylase, the export of its product (maltose) or further metabolism of maltose by a newly identified transglucosidase impairs starch degradation [3].
• Analyses of transgenic and mutant plants demonstrate that plastidic glucan phosphorylase is not required for normal starch breakdown and cast doubt on the presumed essential role of alpha-amylase but do show that beta-amylase is important [3].
• TR-BAMY may be the only beta-amylase of nonphotosynthetic plastids suggesting a redox regulation of starch metabolism in these organelles [4].
• It has been suggested that beta-amylase (BMY) induction during temperature stress in Arabidopsis could lead to starch-dependent maltose accumulation, and that maltose may contribute to protection of the electron transport chain and proteins in the chloroplast stroma during acute stress [5].
• Interestingly, many genes thought to be responsible for cold acclimation such as COR, lipid transfer protein, and beta-amylase, that are highly induced in Arabidopsis leaves, were only expressed at their normal level or weakly induced in the pollen [6].

Chemical compound and disease context of BMY2

• Expression of the gene in E. coli showed that the protein product was a functional beta-amylase that could degrade both starch granules and solubilized amylopectin, while import experiments demonstrated that the beta-amylase was imported and processed into pea chloroplasts [7].

Biological context of BMY2

• Analysis of plants reduced in the presence of this beta-amylase isoform showed that their leaves had a starch-excess phenotype, indicating a defect in starch degradation [7].
• Although the Iba1 and Iba2 mutations did not affect sugar-inducible gene expression in general, the expression of sugar-regulated genes other than the gene for beta-amylase was differentially affected in the Iba1 mutant and Ler plants [8].
• However, we have identified a novel beta-amylase gene, designated ct-Bmy, which is located on chromosome IV of Arabidopsis thaliana [1].
• The N-terminal sequences (AVNGKG MNPDYKAYLMAPLKKI), the C-terminal sequences (SHTSSW), and the amino acid sequences of the five regions in the beta-amylase molecules were determined [2].
• These results suggest that B. cereus beta-amylase has an extra domain which has raw-starch-binding ability and that the domain has considerable sequence homology with those of other amylases or related enzymes from a wide variety of microorganisms [2].

Anatomical context of BMY2

• Among the latter, chloroplast-targeted beta-amylase (At4g17090) and thioredoxin-regulated beta-amylase (TR-BAMY; At3g23920; this work) are experimentally demonstrated to be targeted to plastids [4].

Associations of BMY2 with chemical compounds

• Higher that wild-type levels of beta-amylase in hba1 plants depended on the presence of 1 to 2% sucrose or 1% glucose in the medium, whereas leaves of mutant plants grown with higher levels of sugars had beta-amylase activities similar to those in leaves of wild-type plants [9].
• We identified a mutant of Arabidopsis thaliana ectotype Col-O in which significantly reduced levels of expression of the gene for beta-amylase (AT beta-Amy) were detected in leaves in response to high concentrations of sucrose, glucose or fructose [8].
• Furthermore, trehalose induced the expression of the beta-amylase gene, AT-beta-Amy, in combination with Suc but not when trehalose was supplied alone, indicating that trehalose can modulate sugar-mediated gene expression [10].

Analytical, diagnostic and therapeutic context of BMY2

• The RS 5 antibody cross-reacts with the major form of A. thaliana beta-amylase on immunoblots, and the antibody also binds to the sieve elements of A. thaliana using immunofluorescence microscopy [11].

References