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Genes encoding the vacuolar Na+/H+ exchanger and flower coloration
T Yamaguchi1, S Fukada-Tanaka, Y Inagaki
1National Institute for Basic Biology, Okazaki, 444-8585 Japan.
Plant & Cell Physiology
|May 31, 2001
Summary
Flower color in Japanese morning glories shifts from purple to blue as vacuolar pH rises. A mutation in the Purple (Pr) gene, encoding a vacuolar Na+/H+ exchanger, results in purple flowers due to a lower vacuolar pH.
Area of Science:
- Plant biology
- Molecular genetics
- Biochemistry
Background:
- Vacuolar pH is crucial for flower pigmentation, with increased pH leading to blue hues.
- Japanese morning glory (Ipomoea nil) exhibits a color change from reddish-purple buds to blue flowers, linked to vacuolar pH elevation.
Purpose of the Study:
- To characterize a mutant with altered flower color in Ipomoea nil.
- To investigate the role of the Purple (Pr) gene, encoding a vacuolar Na+/H+ exchanger (InNHX1), in flower coloration.
Main Methods:
- Genetic analysis of a recessive mutant (purple, pr) in Ipomoea nil.
- Functional complementation of the yeast nhx1 mutation using the I. nil Pr (InNHX1) gene.
- Measurement of vacuolar pH in wild-type and mutant flowers.
- Gene expression analysis of InNHX1 in petals.
Main Results:
- The pr mutant exhibits a partial increase in vacuolar pH during flower opening, resulting in purple, not blue, flowers.
- Vacuolar pH in mutant purple flowers is significantly lower than in wild-type blue flowers.
- The InNHX1 gene is highly expressed in petals preceding flower opening, correlating with vacuolar alkalization for blue coloration.
Conclusions:
- The Purple (Pr) gene, encoding InNHX1, is essential for achieving blue flower coloration in Japanese morning glory.
- Vacuolar alkalization mediated by InNHX1 is a key mechanism for blue flower color.
- This study reveals a novel role for vacuolar Na+/H+ exchangers in flower pigmentation beyond salt tolerance.
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