The invention relates to methods of producing a desired phenotype in a plantby manipulation of gene expressionwithin the plant. The method relates to means which inhibit the level of PK220gene expression or activity, wherein a desired phenotypesuch as increased water use efficiency relative to a wild type control plant.The invention also relates to nucleic acid sequencesand constructs useful such methods and methods of generating and isolatingplants having decreased PK220 expressionor activity.