A UBIQUITOUS PLANT HOUSEKEEPING GENE, PAP, ENCODES A MAJOR PROTEIN-COMPONENT OF BELL PEPPER CHROMOPLASTS

We have isolated a cDNA (PAP) corresponding to a single nuclear that e ncodes an approximately 30-kD major protein of bell pepper (Capsicum a nnuum L.) fruit chromoplasts. RNA and protein analyses revealed that, although at a low level, this gene is also expressed in every organ of the plant, the amount of the corresponding transcript and protein dra matically increasing in the latter stages of fruit development. Wester n-blot and immunocytochemical analyses of purified chloroplasts from l eaves and fruits and of chromoplasts from red fruits showed that the e ncoded protein is the major component of plastoglobules and fibrils an d is localized on the outer surface of these lipid structures. Analyse s of PAP in plants belonging to different taxa revealed that it is exp ressed and highly conserved in both monocotyledonous and dicotyledonou s plants. The presence of the protein in plastids not differentiating into chromoplasts indicates that PAP is expressed irrespective of the ontogeny of various plastid lines. In light of our results and since t he encoded protein, identical to that previously named ChrB or fibrill in, is present in plastoglobules from several species and accumulates in the fibrils of bell pepper chromoplast, we propose to designate it as a plastid-lipid-associated protein.