CHROMOPLAST DEVELOPMENT IN RIPENING TOMATO FRUIT - IDENTIFICATION OF CDNAS FOR CHROMOPLAST-TARGETED PROTEINS AND CHARACTERIZATION OF A CDNA-ENCODING A PLASTID-LOCALIZED LOW-MOLECULAR-WEIGHT HEAT-SHOCK PROTEIN

During tomato fruit ripening, photosynthetically competent thylakoid m embranes are broken down and replaced by membranous deposits of carote noids. Few of the proteins involved in this transition have been ident ified. We have used chloroplast protein import assays as a means to id entify two cDNAs that encode proteins destined for the developing chro moplast. One of the cDNAs had unexpected properties and its biological function has not been determined. However, the other cDNA encodes a p lastid-localized low-MW heat shock protein (hsp). The steady state lev el of RNA corresponding to this cDNA increased several-fold during tom ato ripening, and the amount of RNA induced by heat stress increased d ramatically during this process. These observations suggest a new role for this stress protein in protecting the plastid during the dismantl ing of the thylakoid membranes or during the buildup of carotenoids.