(WO200120020) The present invention relates to a method for screening and identification of compounds or compositions useful as herbicides, growth regulators or fungicides involving at least the following steps of addition of the compound or composition to be screened or identified to a culture or culture area of a yeast strain transformed with and expressing one or more plant cell cycle control genes or mutants thereof (phytoyeast) as well as to a control yeast strain; and, determining the effect on the phenotype (growth and/or cell division and/or cell size/shape) of said phytoyeast compared to said control yeast. The invention further relates to a bilogical screening assay (high throughput system) comprising the use of said phytoyeast expressing plant cell cycle control proteins to identify novel compounds or compositions that affect control yeast or phytoyeast phenotype. The present invention also relates to methods for producing a pesticide, herbicide, plant growth regulator or fungicide, comprising the steps of (a) identifying a compound or composition as defined above or a derivative or homologue thereof, and, (b) mixing said compound, composition, derivative or homologue thereof with an acceptable carrier. The invention also relates to the use of said compounds or compositions for inhibiting or stimulating plant growth and/or for increasing crop yield and/or for preventive or curative protection of the plant against fungal infection.
(WO200120020) CLAIMS 1. A method for screening and identification of compounds or compositions useful as herbicides, growth regulators or fungicides involving at least the following steps: (a) addition of the compound or composition to be screened or identified to a culture or culture area of a yeast strain transformed with and expressing one or more plant cell cycle control genes or mutants thereof (phytoyeast) as well as to a control yeast strain; and, (b) determining the effect on the phenotype (growth and/or cell division and/or cell size/shape) of said phytoyeast compared to said control yeast. 2. The method of claim 1 , wherein said plant polynucleic acids are expressed in yeast under the control of a repressible or inducible promoter, any other controlling element and/or culture conditions. 3. The method of claim 1 or 2 wherein said yeast is any strain of Saccharomyces cerevisiae, Candida albicans or more preferably Schizosaccharomyces pombe. 4. The method of any of claims 1 to 3, wherein said transformed yeast strain (phytoyeast) contains a plant cell cycle control gene or mutant thereof which is functionally complementing an essential endogenous cell cycle control gene or mutant thereof, involving at least the steps of: (a) addition of the compound or composition to be screened or identified to a culture or culture area of said phytoyeast expressing said plant cell cycle control protein or a mutant thereof, as well as to a control yeast strain; (b) determining the effect on the phenotype (growth and/or cell division and/or cell size/shape) of said phytoyeast compared to said control yeast; (c) identifying a compound or composition which affects said phenotype of said phytoyeast but not of said control yeast; and, (d) confirming whether said compound or composition also inhibits or stimulates the growth of plants. 5. The method of any of claims 1 to 3, wherein said transformed yeast strain (phytoyeast) expresses a plant cell cycle control gene or dominant mutant thereof, wherein said method involves at least the following steps: (a) addition of the compound or composition to be screened or identified to a culture or culture area of said phytoyeast expressing said plant cell cycle control gene or dominant mutant thereof as well as to a control yeast strain; (b) determining the effect on the phenotype (growth and/or cell division and/or cell size/shape) of said phytoyeast compared to said control yeast; (c) identifying a compound or composition which affects said phenotype of said phytoyeast but not of said control yeast; and (d) confirming whether said compound or composition also inhibits or stimulates the growth of plants. 6. The method of claim 5, wherein said transformed yeast (phytoyeast) expresses a plant cell cycle control gene which does not complement endogenous yeast cell cycle control genes but which affects the phenotype (growth and/or cell division and/or cell size/shape) of said phytoyeast. 7. The method of claim 5, wherein said transformed yeast (phytoyeast) expresses a plant cell cycle control gene with a dominant negative mutation resulting in growth arrest. 8. The method of claim 5, wherein said transformed yeast (phytoyeast) expresses a plant cell cycle control gene with a dominant positive mutation resulting in growth acceleration. 9. The method of any of claims 1 to 3, wherein said transformed yeast (phytoyeast) expresses a first plant cell cycle control gene or mutant thereof with the activity of its encoded protein being modulated by the expression of a second plant cell cycle control gene or mutant thereof, wherein said method comprises the following steps: (a) addition of the compound or composition to be screened or identified to a culture or culture area of a strain of said double transformed yeast (phytoyeast) expressing at least said first and said second plant cell cycle control gene or mutants thereof as well as to said phytoyeast only expressing said first plant cell cycle control gene; (b) determining the effect on the phenotype (growth and/or cell division and/or cell size/shape) of said double transformed phytoyeast expressing at least said first and said second plant cell cycle control gene compared to said phytoyeast only expressing said first plant cell cycle control gene; (c) identifying a compound or composition which affects said phenotype of said double transformed phytoyeast expressing at least said first and said second plant cell cycle control gene compared to said phytoyeast only expressing said first plant cell cycle control gene; and (d) confirming whether said compound or composition also inhibits or stimulates the growth of plants. 10. The method of claim 9, wherein said first plant cell division cycle control protein is preferably encoded by the A. thaliana cdc2a gene or mutant thereof and said second plant cell cycle control protein or mutant thereof is encoded by another cell cycle control gene or mutant thereof, preferably an A. thaliana CKI or mutant thereof. 11 . A method for identifying plant specific compounds or compositions comprising the steps of a method of any of claims 1 to 10 wherein said compound or composition affects the phenotype (growth and/or cell division and/or cell shape/size) of a yeast strain transformed with one or more plant cell cycle control genes (phytoyeast) and not of a wild type control yeast and not of a control yeast expressing an animal or human homologue(s) of the plant cell cycle control gene(s) expressed in the phytoyeast. 12. A method for identifying fungicide compounds or compositions comprising the steps of a method of claim 1 to 10 wherein said compound or composition inhibits growth of the wild type control yeast but not of the mutant control yeast being either a phytoyeast and or a yeast expressing the corresponding animal or human cell cycle control gene. 13. The method for identifying a compound or composition of any of claims 1 to 12, comprising solubilising said test compound or composition in a solvent, diluting it and adding it to the cell culture medium of said yeast strains. 14. The method of any of claims 1 to 13, wherein said compound or composition is added to a disk or to a well on a culture plate, in a standard diffusion assay using solidified media, or is added directly into liquid media. 15. The method of any of claims 1 to 14, wherein said yeast are exposed to a range of concentrations of said test compound or composition. 16. A method of any of claims 1 to 15, wherein the determination of the effect on the phenotype (growth and/or cell division and/or cell size/shape) consists of measuring the decrease or increase of the degree of growth and/or cell division and/or analyzing the phenotype of said phytoyeast and said control yeast upon addition of said compound or composition. 17. Use of transformed yeast cells expressing at least one plant cell cycle control gene or a mutant thereof as defined in any of claims 1 to 3 for the screening or identification of compounds or compositions which abolish, retard or stimulate plant growth. 18. Use of a recombinant vector comprising at least one polynucleic acid encoding at least part of a plant cell cycle control protein or a mutant thereof as defined in any of claims 1 to 3 to transform yeast for the screening or identification of compounds or compositions which abolish, retard or stimulate plant growth. 19. The use of claim 18, wherein said recombinant vector is a plasmid, more particularly a vector comprising a selectable marker and transcriptional control elements for the expression of said plant or animal/human cell cycle control polynucleic acids in yeast. 20. The method or use of any of claims 1 to 19, wherein said plant or animal cell cycle control polynucleic acid is integrated into the yeast genome by random, non-homologous or homologous recombination. 21. A biological screening assay comprising the use of transformed yeast (phytoyeast) as defined in any of claims 1 to 20 expressing plant cell cycle control proteins to identify novel compounds or compositions that affect control yeast or phytoyeast phenotype. 22. The use of a screening assay according to claim 21 for identifying compounds or compositions which act as herbicides, plant growth regulators or fungicides. 23. A high throughput screening system to determine compounds or compositions which act as herbicides, plant growth regulators or fungicides involving a method, use or biological assay of any of claims 1 to 22, preferably a microtiter plate screening system. 24. A compound or composition identifiable by a method according to any of claims 1 to 23. 25. A method for producing a pesticide, herbicide, plant growth regulator or fungicide, comprising the steps of: (a)identifying a compound or composition as defined in any of claims 1 to 24 or a derivative or homologue thereof, and, (b)mixing said compound, composition, derivative or homologue thereof with an acceptable carrier. 26. Use of a compound or composition according to claim 24 in a method according to claim 25 for inhibiting or stimulating plant growth and/or for increasing crop yield and/or for preventive or curative protection of the plant against fungal infection. 27. A yeast strain expressing CDC2a.AF and a cyclin-dependent kinase inhibitor of A. thaliana resulting in an elongated cell type. 28. A compound screening assay comprising the use of a yeast strain of claim 27.
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