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Front. Plant Sci. | doi: 10.3389/fpls.2018.01887

The ability of a charophyte alga hexokinase to restore glucose signaling and glucose repression of gene expression in a glucose-insensitive Arabidopsis hexokinase mutant depends on its catalytic activity

Mikael Ulfstedt1,  Guo-Zhen Hu1,  D. M. Eklund2 and  Hans Ronne1*
  • 1Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Sweden
  • 2Department of Plant Ecology and Evolution, Uppsala University, Sweden

Hexokinases is a family of proteins that is found in all eukaryotes. Hexokinases play key roles in the primary carbon metabolism, where they catalyze the phosphorylation of glucose and fructose, but they have also been shown to be involved in glucose signaling in both yeast and plants. We have characterized the Klebsormidium nitens KnHXK1 gene, the only hexokinase-encoding gene in this charophyte alga. The encoded protein, KnHXK1, is a type B plant hexokinase with an N-terminal membrane anchor localizing the protein to the mitochondrial membranes. We found that KnHXK1 expressed in Arabidopsis thaliana can restore the glucose sensing and glucose repression defects of the glucose-insensitive hexokinase mutant gin2-1. Interestingly, both functions require a catalytically active enzyme, since an inactive double mutant was unable to complement gin2-1. These findings differ from previous results on Arabidopsis AtHXK1 and its orthologues in rice, where catalytic and glucose sensing functions could be separated, but are consistent with recent results on the rice cytoplasmic hexokinase OsHXK7. A model with both catalytic and non-catalytic roles for hexokinases in glucose sensing and glucose repression is discussed.

Keywords: Hexokinase, Glucose repression, Arabidopsis thaliana, Klebsormidium nitens, Saccharomyces cerevisiae, glucose signaling

Received: 24 Aug 2018; Accepted: 06 Dec 2018.

Edited by:

Nigel G. Halford, Rothamsted Research (BBSRC), United Kingdom

Reviewed by:

Patricia León, National Autonomous University of Mexico, Mexico
Filip Rolland, KU Leuven, Belgium  

Copyright: © 2018 Ulfstedt, Hu, Eklund and Ronne. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Hans Ronne, Swedish University of Agricultural Sciences, Department of Forest Mycology and Plant Pathology, Uppsala, 75651, Uppsala, Sweden, Hans.Ronne@slu.se