Abstract
In the final step of cytokinin biosynthesis, the main pathway is the elimination of a ribose-phosphate moiety from the cytokinin nucleotide precursor by phosphoribohydrolase, an enzyme encoded by a gene named LONELY GUY (LOG). This reaction accounts for most of the cytokinin supply needed for regulating plant growth and development. In contrast, the LOG-independent pathway, in which dephosphorylation and deribosylation sequentially occur, is also thought to play a role in cytokinin biosynthesis, but the gene entity and physiological contribution have been elusive. In this study, we profiled the phytohormone content of chromosome segment substitution lines of Oryza sativa and searched for genes affecting the endogenous levels of cytokinin ribosides by quantitative trait loci analysis. Our approach identified a gene encoding an enzyme that catalyzes the deribosylation of cytokinin nucleoside precursors and other purine nucleosides. The cytokinin/purine riboside nucleosidase 1 (CPN1) we identified is a cell wall–localized protein. Loss-of-function mutations ( cpn1 ) were created by inserting a Tos17 -retrotransposon that altered the cytokinin composition in seedling shoots and leaf apoplastic fluid. The cpn1 mutation also abolished cytokinin riboside nucleosidase activity in leaf extracts and attenuated the trans -zeatin riboside-responsive expression of cytokinin marker genes. Grain yield of the mutants declined due to altered panicle morphology under field-grown conditions. These results suggest that the cell wall–localized LOG-independent cytokinin activating pathway catalyzed by CPN1 plays a role in cytokinin control of rice growth. Our finding broadens our spatial perspective of the cytokinin metabolic system.
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Claims 7
Claim · model-written summary
A gene encoding an enzyme that deribosylates cytokinin nucleoside precursors and other purine nucleosides was identified.
Not reportedTaxon
Verbatim
e0“Our approach identified a gene encoding an enzyme that catalyzes the deribosylation of cytokinin nucleoside precursors and other purine nucleosides.”
Claim · model-written summary
CPN1 is localized to the cell wall.
Not reportedTaxon
Verbatim
e0“The cytokinin/purine riboside nucleosidase 1 (CPN1) we identified is a cell wall–localized protein.”
Claim · model-written summary
cpn1 mutations altered cytokinin composition in seedling shoots and leaf apoplastic fluid.
- Organ / stage
- seedling shoots and leaf apoplastic fluide0
- Gene
- cpn1e0
- Outcome
- cytokinin compositione0
- Direction
- alterede0
Not reportedTaxon
Verbatim
e0“Loss-of-function mutations ( cpn1 ) were created by inserting a Tos17 -retrotransposon that altered the cytokinin composition in seedling shoots and leaf apoplastic fluid.”
Claim · model-written summary
The cpn1 mutation abolished cytokinin riboside nucleosidase activity in leaf extracts.
- Organ / stage
- leaf extractse0
- Gene
- cpn1e0
- Outcome
- cytokinin riboside nucleosidase activitye0
- Direction
- abolishede0
Not reportedTaxon
Verbatim
e0“The cpn1 mutation also abolished cytokinin riboside nucleosidase activity in leaf extracts and attenuated the trans -zeatin riboside-responsive expression of cytokinin marker genes.”
Claim · model-written summary
The cpn1 mutation attenuated trans-zeatin-riboside-responsive cytokinin marker gene expression.
- Gene
- cpn1e0
- Outcome
- trans -zeatin riboside-responsive expression of cytokinin marker genese0
- Direction
- attenuatede0
Not reportedTaxon
Verbatim
e0“The cpn1 mutation also abolished cytokinin riboside nucleosidase activity in leaf extracts and attenuated the trans -zeatin riboside-responsive expression of cytokinin marker genes.”
Claim · model-written summary
Grain yield declined in cpn1 mutants under field-grown conditions.
Not reportedTaxon
Verbatim
e0“Grain yield of the mutants declined due to altered panicle morphology under field-grown conditions.”
Claim · model-written summary
Altered panicle morphology was implicated in reduced grain yield of cpn1 mutants.
Not reportedTaxon
Verbatim
e0“Grain yield of the mutants declined due to altered panicle morphology under field-grown conditions.”