Starch is an important energy-storage compound for plants and it makes up a significant portion of the human diet. In leaves, starch accumulates in chloroplasts during the day, and is broken down at night to provide energy for the plant when photosynthesis is not possible. The enzyme responsible for breaking down most of the starch at night is β-amylase (BAM). There are nine BAM or BAM-like genes in the Arabidopsis genome, six of which (BAM 1, -2, -3, -4, -6 and -9) encode proteins that are targeted to chloroplasts. Of these, only BAM1, -2, -3, and -6 are catalytically active. The focus of this work is on BAM9, which is located in chloroplasts but is catalytically inactive. Preliminary evidence from a mutant lacking BAM9, and from its structure and pattern of expression, suggests that it might play a role in regulating starch metabolism.
The three objectives of this work are to 1) investigate the influence of BAM9 on the diurnal activity of the four active plastidic BAMs in leaf extracts of mutants lacking the proteins, 2) characterize the ability of pure BAM9 to bind starch and various small carbohydrates, and 3) identify and characterize protein(s) that bind to BAM9. It is hypothesized that BAM9 acts to inhibit the activity of one or more of the active BAMs at dawn when starch degradation normally stops.
This research will help to characterize the physiological functions of five plastid-targeted β-amylases in Arabidopsis, and will shed light on how starch metabolism is regulated in leaves, especially at the night/day transition. The project will also train a number of undergraduates planning to pursue careers in science, and a teaching/research postdoctoral scholar planning to pursue a career at a predominantly undergraduate institution.
