Journal Article

Characterization of a Novel Na<sup>+</sup>/H<sup>+</sup> Antiporter Gene <i>InNHX2</i> and Comparison of <i>InNHX2</i> with <i>InNHX1</i>, Which is Responsible for Blue Flower Coloration by Increasing the Vacuolar pH in the Japanese Morning Glory

Makoto Ohnishi, Sachiko Fukada-Tanaka, Atsushi Hoshino, Jitsuya Takada, Yoshishige Inagaki and Shigeru Iida

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 2, pages 259-267
Published in print February 2005 | ISSN: 0032-0781
Published online February 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci028
Characterization of a Novel Na+/H+ Antiporter Gene InNHX2 and Comparison of InNHX2 with InNHX1, Which is Responsible for Blue Flower Coloration by Increasing the Vacuolar pH in the Japanese Morning Glory

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The reddish-purple buds of the wild-type Japanese morning glory (Ipomoea nil) change into blue open flowers, and the shift in the flower coloration correlates with an increase in the vacuolar pH of the flower epidermal cell. In the mutant deficient in the InNHX1 gene for the vacuolar Na+/H+ antiporter, the vacuolar alkalization occurs only partially, and reddish-purple buds become purple open flowers. While most of the plant NHX genes characterized are generally expressed in leaves, stems and roots and induced by NaCl treatment, the InNHX1 gene is expressed predominantly in the flower limbs at around 12 h before flower opening. It is expressed very sparsly in leaves, stems and roots, and no induction occurs in response to NaCl treatment. Here, we identified a novel vacuolar Na+/H+ antiporter gene InNHX2, which is expressed in leaves, stems and roots and is induced in response to NaCl treatment. In addition, relatively higher expression of InNHX2 was observed in the flower limbs shortly before flower opening. We also discovered that both the InNHX1 and InNHX2 proteins can catalyze both Na+ and K+ transport into vacuoles. These results suggest that InNHX2 performs dual functions: to confer salt tolerance on the plant and to promote partial vacuolar alkalization in the petals. The implication is that the InNHX2 protein is probably one of the components responsible for converting reddish-purple buds into purple open flowers by partially increasing the vacuolar pH in the absence of major InNHX1 activity.

Keywords: Flower coloration; Japanese morning glory (Ipomoea nil); NHX genes; Salt tolerance; Vacuolar Na+/H+ antiporters; CaMV, cauliflower mosaic virus; GFP, green fluorescent protein

Journal Article.  6429 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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