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Differential expression and properties of starch branching enzyme isoforms in developing wheat endosperm
M K Morell1, A Blennow, B Kosar-Hashemi
1Cooperative Research Centre for Plant Science, Canberra, Australia. morell@rsbs-central.anu.edu.au
Plant Physiology
|January 1, 1997
Summary
Researchers identified and characterized three starch branching enzymes (BE) in wheat endosperm, revealing distinct roles and expression patterns during development. These enzymes, WBE-I and WBE-II, show differences in amylose affinity and activation, impacting starch biosynthesis.
Area of Science:
- Plant biochemistry
- Molecular biology
- Wheat genetics
Background:
- Starch branching enzymes (BE) are crucial for synthesizing amylose and amylopectin in plants.
- Understanding BE function in wheat (Triticum aestivum) endosperm is key to improving starch quality and yield.
Purpose of the Study:
- To purify and characterize three distinct starch branching enzyme (BE) forms from developing wheat endosperm.
- To determine the genetic locations and expression patterns of these wheat BEs.
- To compare the kinetic properties and regulatory mechanisms of different wheat BE classes.
Main Methods:
- Partial purification and characterization of wheat starch branching enzymes.
- Immunological cross-reactivity assays using anti-maize BE antibodies.
- N-terminal amino acid sequencing and comparison with known BE sequences.
- Analysis of nullisomic-tetrasomic wheat lines for gene localization.
- Enzyme kinetic assays measuring substrate affinity and activation by phosphate.
Main Results:
- Three BE forms (WBE-IAD, WBE-IB, and WBE-II) were identified, related to maize BE I and BE II classes.
- WBE-IB is located on chromosome 7B; WBE-IAD components are on chromosomes 7A and 7D.
- WBE-II shows constant expression, while WBE-IAD and WBE-IB are preferentially expressed in late endosperm development.
- WBE-I isoforms exhibit higher amylose affinity and greater activation by phosphate compared to WBE-II.
Conclusions:
- Wheat endosperm possesses multiple BE isoforms with distinct biochemical properties and expression profiles.
- Differential regulation and kinetics of wheat BEs suggest specialized roles in starch biosynthesis.
- These findings provide insights into the genetic control and functional diversity of starch synthesis in wheat.