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Tomato fructokinases exhibit differential expression and substrate regulation
Plant Physiology
|May 22, 1998
Summary
Tomato plants have two fructokinase genes, Frk1 and Frk2, that are sugar-regulated. Frk2 shows distinct spatial expression and substrate inhibition, suggesting a role in starch storage.
Area of Science:
- Plant molecular biology
- Biochemistry
Background:
- Two genes, Frk1 and Frk2, encode fructokinase in tomato (Lycopersicon esculentum L.).
- These genes are known to be expressed in tomato plants.
Purpose of the Study:
- To further characterize the spatial expression and enzymatic properties of Frk1 and Frk2 proteins.
- To understand the distinct roles of Frk1 and Frk2 in tomato plants.
Main Methods:
- Investigated spatial expression using in situ hybridization.
- Expressed Frk1 and Frk2 cDNAs in a mutant yeast line defective in hexose phosphorylation.
- Assessed fructokinase activity in vitro and substrate inhibition.
Main Results:
- Frk1 and Frk2 mRNA levels were coordinately induced by exogenous sugar.
- Frk1 and Frk2 exhibited distinct spatial expression patterns.
- Both Frk1 and Frk2 proteins showed fructokinase activity in yeast.
- Frk2 activity was inhibited by high fructose concentrations, unlike Frk1.
Conclusions:
- Frk2 is distinguishable from Frk1 by substrate inhibition sensitivity and expression patterns.
- Frk2's distinct characteristics suggest a primary role in plant cells specialized for starch storage.