The present invention discloses a method for screening for and identifying a desirable plant improving trait, said method comprises steps of: (a) obtaining genetic material from a sampling of a predefined source and (b) constructing an expression library from said genetic material. The aforementioned method further comprises steps of: (c) producing plants transformed with said expression library at a transformation efficiency of at least 0.05%-30%, representing at least 102-1010 transgenes; (d) screening for transformed plants expressing said desirable trait; and (e) identifying said transgene of said transformed plants expressing said desirable trait.