Identification of a promoter region responsible for the senescence-specific expression of SAG12

SAG12, an Arabidopsis gene encoding a cysteine protease, is expressed only in senescent tissues. Studies of the expression patterns of a variety of ge nes showing senescence-specific or senescence-preferential expression indic ate that plant senescence involves multiple regulatory pathways. In this st udy it is shown that the expression of SAG12 is specifically activated by d evelopmentally controlled senescence pathways but not by stress- or hormone -controlled pathways. Using SAG12 as a molecular marker for the study of de velopmental senescence, we show that cytokinin, auxin, and sugars can repre ss developmental senescence at the molecular level. Studies using promoter deletions and recombination of promoter fragments indicate that a highly co nserved region of the SAG12 promoter is responsible for senescence-specific regulation, while at least two other regions of the SAG12 promoter are imp ortant for full promoter activity. Extracts from young and senescent Arabid opsis leaves contain factors that exhibit differential binding to the senes cence-responsive promoter element.