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Int. J. Mol. Sci. 2017, 18(11), 2398; https://doi.org/10.3390/ijms18112398

Identification, Expression, and Functional Analysis of the Fructokinase Gene Family in Cassava

1
Key Laboratory of Biology and Genetic Resources of Tropical Crops, Ministry of Agriculture, Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
2
College of Agriculture, Hainan University, Haikou 570228, China
3
Prisys Biotechnologies Company Limited, Shanghai 201203, China
4
College of Life Science and Biotechnology, Heilongjiang Bayi Agricultural University, Daqing 163319, China
These authors contributed equally to this work.
*
Authors to whom correspondence should be addressed.
Received: 27 September 2017 / Revised: 6 November 2017 / Accepted: 7 November 2017 / Published: 12 November 2017
(This article belongs to the Section Biochemistry)
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Abstract

Fructokinase (FRK) proteins play important roles in catalyzing fructose phosphorylation and participate in the carbohydrate metabolism of storage organs in plants. To investigate the roles of FRKs in cassava tuber root development, seven FRK genes (MeFRK17) were identified, and MeFRK16 were isolated. Phylogenetic analysis revealed that the MeFRK family genes can be divided into α (MeFRK 1, 2, 6, 7) and β (MeFRK 3, 4, 5) groups. All the MeFRK proteins have typical conserved regions and substrate binding residues similar to those of the FRKs. The overall predicted three-dimensional structures of MeFRK1–6 were similar, folding into a catalytic domain and a β-sheet ‘‘lid” region, forming a substrate binding cleft, which contains many residues involved in the binding to fructose. The gene and the predicted three-dimensional structures of MeFRK3 and MeFRK4 were the most similar. MeFRK1–6 displayed different expression patterns across different tissues, including leaves, stems, tuber roots, flowers, and fruits. In tuber roots, the expressions of MeFRK3 and MeFRK4 were much higher compared to those of the other genes. Notably, the expression of MeFRK3 and MeFRK4 as well as the enzymatic activity of FRK were higher at the initial and early expanding tuber stages and were lower at the later expanding and mature tuber stages. The FRK activity of MeFRK3 and MeFRK4 was identified by the functional complementation of triple mutant yeast cells that were unable to phosphorylate either glucose or fructose. The gene expression and enzymatic activity of MeFRK3 and MeFRK4 suggest that they might be the main enzymes in fructose phosphorylation for regulating the formation of tuber roots and starch accumulation at the tuber root initial and expanding stages. View Full-Text
Keywords: cassava; fructokinase; gene expression; yeast complementation; enzyme activities cassava; fructokinase; gene expression; yeast complementation; enzyme activities
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Yao, Y.; Geng, M.-T.; Wu, X.-H.; Sun, C.; Wang, Y.-L.; Chen, X.; Shang, L.; Lu, X.-H.; Li, Z.; Li, R.-M.; Fu, S.-P.; Duan, R.-J.; Liu, J.; Hu, X.-W.; Guo, J.-C. Identification, Expression, and Functional Analysis of the Fructokinase Gene Family in Cassava. Int. J. Mol. Sci. 2017, 18, 2398.

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