In a transgenic plant, a housekeeping gene could be expressed under the control of the CAB promoter or similar promoter expressed prior to senescence. It is well es
tablished that the CAB promoter drives expression in photosynthetic leaves and is rapidly attenuated once senescence begins (Fig. 2 and Lohman et al. 1994). Thus, RAN1 or an- other gene could be expressed before senescence begins possibly allowing normal development of a mutant. Once se- nescence begins, the expression of the gene would decrease allowing researchers to study the progression of senescence in the absence of the gene to be studie