Subcellular Localization and Changes in mRNA Abundance of CEBP, a Nuclear-Encoded Chloroplast Protein, During Flower Development and Senescence

CEBP, a nuclear-encoded chloroplast protein, has been previously cloned as a putative transcription factor involved in ethylene signaling in carnation development and senescence. In order to more clearly define CEBP role and function, we carried out experiments to define its pattern of mRNA abundance and possible subcellular localization. Changes in CEBP mRNA abundance showed a dramatic drop from anthesis to open flower stage of development immediately preceding the ethylene climacteric associated with flower senescence. A similar but less dramatic decrease in CEBP was observed upon ethylene exposure, again before endogenous climacteric ethylene was observed. The pattern of CEBP mRNA abundance suggests a response to or involvement in the initial steps of the petal senescence process. GFP co-localization showed that a GFP–CEBP construct was directed to the nucleus, whereas a CEBP–GFP construct localized to the chloroplast. Nuclear localization was expected as CEBP was cloned as an ethylene-responsive element-binding protein or transcription factor. The role and function of CEBP in the chloroplast, however, remains unclear. Future lines of inquiry based on our results are discussed.