Regulated expression of cytokinin-Modulating genes

Abstract

This invention relates generally to the field of plant molecular biology. More specifically, this invention relates to methods and reagents for the temporal and/or spatial expression of genes that affect metabolically effective levels of cytokinins in plant seeds and related maternal tissue. This invention further relates to transgenic plants having enhanced levels of cytokinin expression wherein the transgenic plant exhibits useful characteristics, including: improved seed size, decreased tip kernel abortion, increased seed set during unfavorable environmental conditions, and stability of yield.

1 . A method for producing transgenic plants comprising: 
 transforming plant host cells with a genetic construct comprising 
 an isolated polynucleotide encoding a gene product involved in cytokinin modulation, wherein the gene product is not isopentenyl transferase,  
 operably linked to a promoter driving expression in a temporally-and/or spatially-preferred manner,  
   wherein the isolated polynucleotide is expressed in the transformed plant cells;    and regenerating transgenic plants from said transformed plant cells, wherein said plants exhibit one or more traits selected from the group consisting of increased seed size and increased seed number relative to a plant not transformed with said construct.    
     
     
         2 . The method of  claim 1  wherein said promoter drives expression in developing plant seeds.  
     
     
         3 . The method of  claim 1  wherein the gene product involved in cytokinin modulation affects the level or activity of cytokinin oxidase.  
     
     
         4 . The method of  claim 3  wherein the level or activity of cytokinin oxidase is reduced.  
     
     
         5 . A transgenic plant comprising a genetic construct comprising 
 an isolated polynucleotide encoding a gene product involved in cytokinin modulation, wherein the gene product is not isopentenyl transferase,    operably linked to a promoter driving expression in a temporally- and/or spatially-preferred manner,    wherein said transgenic plant exhibits one or more traits selected from the group consisting of increased seed size and increased seed number relative to a plant not transformed with said construct.    
     
     
         6 . The plant of  claim 5  wherein said promoter drives expression in developing plant seeds.  
     
     
         7 . The plant of  claim 5  wherein the gene product involved in cytokinin modulation affects the level or activity of cytokinin oxidase.  
     
     
         8 . The plant of  claim 7  wherein the level or activity of cytokinin oxidase is reduced.  
     
     
         9 . An isolated recombinant DNA comprising a promoter directing temporal and/or spatial gene expression in developing plant seed operably linked to a polynucleotide encoding a gene product involved in cytokinin modulation, wherein said gene product is not isopentenyl transferase.  
     
     
         10 . The DNA according to  claim 9  wherein said gene product involved in cytokinin modulation affects the level or activity of cytokinin oxidase.  
     
     
         11 . A method for increasing seed number and/or seed size, comprising stably transforming plant host cells with a genetic construct, said construct comprising a promoter which drives expression in developing seeds, operably linked to an isolated polynucleotide encoding a gene product involved in cytokinin modulation, wherein said gene product is not isopentenyl transferase, and regenerating plants from said cells, wherein the plants exhibit increased seed number and/or seed size compared to plants not transformed with said construct.  
     
     
         12 . The method according to  claim 11  wherein said expression is initiated within the range of from about 14 days prior to pollination to about 25 days after pollination.  
     
     
         13 . The method according to  claim 11  wherein said expression is initiated within the range of from about 14 days prior to pollination to about 21 days after pollination.  
     
     
         14 . The method according to  claim 11  wherein said expression is initiated within the range of from about 14 days prior to pollination to about 12 days after pollination.  
     
     
         15 . The method according to  claim 11  wherein said expression is initiated within the range of from about 14 days prior to pollination to zero days after pollination.