Functional and structural characterization of plastidic starch phosphorylase during barley endosperm development

Area of Science:

• Biochemistry
• Plant Biology
• Molecular Biology

Background:

• Starch biosynthesis is crucial for nutrition and global carbon flux.
• Two pathways exist: starch synthases (using ADP-glucose) and starch phosphorylase (Pho1, using glucose-1-phosphate).
• The specific role of the Pho1 pathway in starch production remains largely unknown.

Purpose of the Study:

• To investigate the role of barley starch phosphorylase (HvPho1) in starch biosynthesis within barley endosperm.
• To analyze HvPho1 protein levels, enzyme activity, and structure-function relationships during endosperm development.

Main Methods:

• Analysis of HvPho1 protein production and enzyme activity throughout barley endosperm development.
• Characterization of HvPho1 structure-function relationships.
• In vitro enzymatic assays using purified recombinant HvPho1.

Main Results:

• HvPho1 protein is present and active at the beginning of barley endosperm development.
• Purified HvPho1 can synthesize alpha-1,4 glucans de novo from glucose-1-phosphate (G1P) as the sole substrate.
• HvPho1 exhibits low affinity for large polysaccharides, indicating substrate specificity.

Conclusions:

• HvPho1 plays a significant role in the initiation phase of starch biosynthesis in barley endosperm.
• The enzyme's ability to use G1P suggests a distinct contribution to polysaccharide synthesis.