Multiple, distinct isoforms of sucrose synthase in pea

Area of Science:

• Plant molecular biology
• Biochemistry
• Genetics

Background:

• Sucrose synthase (Sus) plays a key role in sucrose metabolism in plants.
• Pea (Pisum sativum) possesses three distinct Sus isoforms: Sus1, Sus2, and Sus3.
• Understanding the functional differentiation of these isoforms is crucial for comprehending plant carbon partitioning.

Purpose of the Study:

• To clone and characterize the three pea Sus isoforms (Sus1, Sus2, Sus3).
• To investigate the kinetic properties and expression patterns of these isoforms.
• To elucidate the in vivo functional differences between Sus isoforms using mutant analysis.

Main Methods:

• Gene cloning of pea Sus1, Sus2, and Sus3.
• Expression of recombinant proteins in Escherichia coli for kinetic analysis.
• Analysis of gene expression patterns in different pea organs and developmental stages.
• Phenotypic analysis of rug4 pea mutants with altered Sus1 expression.

Main Results:

• Distinct expression patterns were observed for Sus1, Sus2, and Sus3 in pea organs and during development.
• Recombinant Sus isoforms exhibited subtle but significant differences in kinetic properties.
• Pea rug4 mutants lacking Sus1 protein showed a 95% reduction in embryo Sus activity.
• Embryo starch content decreased by 30% in rug4 mutants, while cellulose content remained unaffected.

Conclusions:

• The three pea sucrose synthase isoforms (Sus1, Sus2, Sus3) exhibit distinct kinetic properties and expression profiles.
• Evidence from rug4 mutants suggests that Sus1 plays a significant role in channeling carbon towards starch synthesis in pea embryos.
• Isoforms of sucrose synthase likely direct sucrose-derived carbon to different metabolic pathways within the cell.