Structure, expression, and functional analysis of the hexokinase gene family in rice (Oryza sativa L.)

• Published in: Planta Vol. 224; no. 3; pp. 598 - 611
• Main Authors: Cho, J.I, Ryoo, N, Ko, S, Lee, S.K, Lee, J, Jung, K.H, Lee, Y.H, Bhoo, S.H, Winderickx, J, An, G
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01.08.2006; Springer; Springer Nature B.V
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chloroplasts; Chromosome Mapping; Classical and quantitative genetics. Population genetics. Molecular genetics; Cloning, Molecular; Complementary DNA; conserved sequences; Evolution, Molecular; Flowers - enzymology; Flowers - growth & development; Fructose - metabolism; Fundamental and applied biological sciences. Psychology; Gene expression; gene expression regulation; Generalities. Genetics. Plant material; Genes; Genetic Complementation Test; Genetics and breeding of economic plants; genomics; Glucose - metabolism; Green Fluorescent Proteins - analysis; hexokinase; Hexokinase - chemistry; Hexokinase - genetics; Hexokinase - physiology; Hexoses; molecular cloning; Molecular genetics; Multigene Family; Oryza - enzymology; Oryza - genetics; Oryza - growth & development; Oryza sativa; Phylogeny; Plant cells; Plant Leaves - enzymology; Plant Leaves - growth & development; plant proteins; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - physiology; Plant Roots - enzymology; Plant Roots - growth & development; Plants; Plants, Genetically Modified - cytology; Plants, Genetically Modified - metabolism; Proteins; recombinant fusion proteins; Recombinant Fusion Proteins - analysis; Rice; Saccharomyces cerevisiae; Seeds; Seeds - enzymology; Seeds - growth & development; sequence analysis; Sugars; Yeasts; Yeasts - genetics; Monocotyledones; Seeds; Enzyme; Growth; Transferases; Genomics; Gene structure; Plant leaf; Plastid; Gene expression; Hexokinase; Yeast complementation; Oryza; Complementary DNA; Gene; Gramineae; Angiospermae; Green fluorescent protein; Subcellular localization; Development; Spermatophyta; Pollen; Mutation; Chloroplast
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-006-0251-y

Hexokinase (HXK) is a dual-function enzyme that both phosphorylates hexose to form hexose 6-phosphate and plays an important role in sugar sensing and signaling. To investigate the roles of hexokinases in rice growth and development, we analyzed rice sequence databases and isolated ten rice hexokinase cDNAs, OsHXK1 (Oryza sativa Hexokinase 1) through OsHXK10. With the exception of the single-exon gene OsHXK1, the OsHXKs all have a highly conserved genomic structure consisting of nine exons and eight introns. Gene expression profiling revealed that OsHXK2 through OsHXK9 are expressed ubiquitously in various organs, whereas OsHXK10 expression is pollen-specific. Sugars induced the expression of three OsHXKs, OsHXK2, OsHXK5, and OsHXK6, in excised leaves, while suppressing OsHXK7 expression in excised leaves and immature seeds. The hexokinase activity of the OsHXKs was confirmed by functional complementation of the hexokinase-deficient yeast strain YSH7.4-3C (hxk1, hxk2, glk1). OsHXK4 was able to complement this mutant only after the chloroplast-transit peptide was removed. The subcellular localization of OsHXK4 and OsHXK7, observed with green fluorescent protein (GFP) fusion constructs, indicated that OsHXK4 is a plastid-stroma-targeted hexokinase while OsHXK7 localizes to the cytosol.