ABSTRACT
One of the rare sugars, D-allose, which is the epimer of D-glucose at C3, has an inhibitory effect on rice growth, but the molecular mechanisms of the growth inhibition by D-allose were unknown. The growth inhibition caused by D-allose was prevented by treatment with hexokinase inhibitors, D-mannoheptulose and N-acetyl-D-glucosamine. Furthermore, the Arabidopsis glucose-insensitive2 (gin2) mutant, which is a loss-of-function mutant of the glucose sensor AtHXK1, showed a D-allose-insensitive phenotype. D-Allose strongly inhibited the gibberellin-dependent responses such as elongation of the second leaf sheath and induction of α-amylase in embryo-less half rice seeds. The growth of the slender rice1 (slr1) mutant, which exhibits a constitutive gibberellin-responsive phenotype, was also inhibited by D-allose, and the growth inhibition of the slr1 mutant by D-allose was also prevented by D-mannoheptulose treatment. The expressions of gibberellin-responsive genes were down-regulated by D-allose treatment, and the down-regulations of gibberellin-responsive genes were also prevented by D-mannoheptulose treatment. These findings reveal that D-allose inhibits the gibberellin-signaling through a hexokinase-dependent pathway.
Subject(s)
Gene Expression Regulation, Plant/drug effects , Gibberellins/metabolism , Glucose/pharmacology , Hexokinase/metabolism , Oryza/drug effects , Signal Transduction/drug effects , Arabidopsis/genetics , Arabidopsis/growth & development , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Down-Regulation , Gene Expression Regulation, Plant/physiology , Gibberellins/pharmacology , Hexokinase/genetics , Mutation , Oryza/enzymology , Oryza/genetics , Oryza/growth & development , Phenotype , Plant Leaves/drug effects , Plant Leaves/growth & development , Plant Proteins/genetics , Plant Proteins/metabolism , Plant Shoots/drug effects , Plant Shoots/growth & development , Seedlings/drug effects , Seedlings/growth & development , alpha-Amylases/genetics , alpha-Amylases/metabolismABSTRACT
We examined rice responses to a rare sugar, d-psicose. Rice growth was inhibited by d-psicose but not by common sugars. Microarray analysis revealed that d-psicose treatment caused an upregulation of many defense-related genes in rice, and dose-dependent upregulation of these genes was confirmed by quantitative reverse-transcription polymerase chain reaction. The level of upregulation of defense-related genes by d-psicose was low compared with that by d-allose, which is another rare sugar known to confer induction of resistance to rice bacterial blight in rice. Treatment with d-psicose conferred resistance to bacterial blight in rice in a dose-dependent manner, and the results indicate that d-psicose might be a candidate plant activator for reducing disease development in rice.
