Structure, expression, and functional analysis of the hexokinase gene family in rice (Oryza sativa L.).
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.
Cho
Jung-Il
JI
Plant Metabolism Research Center & Graduate School of Biotechnology, Kyung Hee University, 449-701 Yongin, Republic of South Korea.
Ryoo
Nayeon
N
Ko
Seho
S
Lee
Sang-Kyu
SK
Lee
Junok
J
Jung
Ki-Hong
KH
Lee
Youn-Hyung
YH
Bhoo
Seong Hee
SH
Winderickx
Joris
J
An
Gynheung
G
Hahn
Tae-Ryong
TR
Jeon
Jong-Seong
JS
D002874:Chromosome Mapping; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D035264:Flowers / Q000201:enzymology / Q000254:growth & development; D005632:Fructose / Q000378:metabolism; D005816:Genetic Complementation Test; D005947:Glucose / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000032:analysis; D006593:Hexokinase / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D005810:Multigene Family; D012275:Oryza / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D010802:Phylogeny; D018515:Plant Leaves / Q000201:enzymology / Q000254:growth & development; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D018517:Plant Roots / Q000201:enzymology / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000166:cytology / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000032:analysis; D012639:Seeds / Q000201:enzymology / Q000254:growth & development; D015003:Yeasts / Q000235:genetics
D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005632:Fructose; D006593:Hexokinase; D005947:Glucose