RUI: Structure, function and evolutionary history of beta-amylase2 (BAM2) in plants

James Madison University, Harrisonburg VA

Investigators

Abstract

Starch is an important carbon- and energy-storage compound in plants and it has widespread use in industry and as part of the human diet. With this project the researchers aim to better understand the structure and function of a plant enzyme that they suspect plays and unusual role in starch metabolism. Potential long-term benefits of the research include modified crops that contain starch with properties suitable for improved food and industrial applications. In some plants this enzyme is encoded by a complex gene, the understanding of which could shed light on how genes evolve. The research will be carried out at a predominantly undergraduate institution and involve at least 12 undergraduates helping prepare them for graduate school and careers in science. The students will be involved in all aspects of the work. In addition, the project will support a postdoctoral scholar that will obtain valuable teaching experience in lectures and laboratories of introductory and advanced courses, as well as bringing valuable intellectual and technical assets to the lab. Most importantly, they will be able to develop undergraduate research mentoring skills and acquire practical advice for building a successful career at a predominantly undergraduate institution. Starch is a complex polymer of glucose composed mostly of amylopectin, a highly branched molecule with layers of short chains that are 12-15 glucose units long. In green leaves starch accumulates during the day and is broken down at night so that the leaf can continue to export energy to the entire plant even when photosynthesis is not active. One of the key enzymes known to play an important role in starch degradation is beta-amylase, which hydrolyzes the disaccharide maltose from the ends of amylopectin. The researchers recently discovered that one of the beta-amylases in Arabidopsis called BAM2 is unlike all of the other characterized BAMs in that it is a tetramer, requires K+ for activity, possesses a secondary starch-binding site, and has sigmoidal kinetics. Based on these properties the researchers developed a hypothesis that BAM2 plays a role in starch synthesis as a trimming enzyme to ensure that the short amylopectin chains are of the proper length. To test this hypothesis, they will investigate the catalytic and starch-binding properties of the wildtype and mutant enzymes in detail. In addition, the function of the enzyme will be tested by characterizing the structure of starch isolated from wildtype and mutant plants lacking BAM2. The researchers will also investigate the localization and properties of the BAM2-like protein in rice plants that appears to be part of a longer BAM7 gene with two putative transcriptional start sites. Understanding the role of BAM2 in starch metabolism could have a significant impact on biotechnological efforts to enhance starch yield in crops. The experiments described here may shed light on how starch binding to an allosteric surface of BAM2 influences its catalytic activity. The work may also reveal how novel genes can be generated by fusion events and how they can evolve through duplication and neofunctionalization. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.