Chromoplast-Targeted Proteins in Tomato (Lycopersicon esculentum Mill.) Fruit

Abstract

The chloroplast to chromoplast transition during tomato (Lycopersicon esculenfum Mill.) fruit ripening i s characterized by a dramatic change in plastid structure and function. We have asked whether this process is mediated by an increase in the steady-state leve1 of RNA for plastid targeted proteins. Assays for import of radiolabeled translation products into isolated pea (Pisum safivum 1.) chloroplasts were used to monitor levels of chromoplasttargeted proteins at four stages of tomato fruit development. We have found striking increases during development in levels of translatable RNA for two such proteins. Additionally, the import of in vitro translation products was examined for seven individual cDNA clones known to encode RNA that increase during fruit ripening. Three of these clones produced in vitro translation products that were imported into pea chloroplasts. This implies that there is synthesis and import of new proteins during the transition from chloroplast to chromoplast and that the plastid conversion is an active developmental program rather than a simple decline in synthesis of the photosynthetic apparatus. Furthermore, our results demonstrate the utility of this method for identification of structural genes involved in plastid morphogenesis.

Isolation and characterisation of a melon cDNA clone encoding phytoene synthase

“…We suggest that the most probable cleavage site for the melon PSY is after or near the 83rd amino acid. Cleavage in this region would generate a mature PSY of 38 kDa which is in agreement with the estimated size for the PSY from tomato either by immunoblotting [12] or by import assays with heterologous systems [4,22]. It has been observed that there is stronger conservation among the amino acid sequences of transit peptides encoded by the same gene from different plants than among those encoded from different genes of the same plant [29].…”

“…These cleavage sites would generate tomato PSY proteins that are much smaller than those actually observed. The import studies of Lawrence et al [22] suggest that the tomato PSY may be cleaved to a 41 kDa protein. Import assays with heterologous systems have not proved to be absolutely reliable for correct proces sing of mature proteins.…”

“…Other evidence suggests that phytoene synthase is a peripheral membrane protein because, although it is located in the stroma, there is a labile association with the plastid membrane in daffodil (Narcissus pseudonarcissus) flower chromoplasts [21 ], in spinach (Spinacia oleracea) chloroplasts [23] and in mustard (Sinapis alba) seedling etioplasts and etiochloroplasts [24]. Import assays with heterologous systems have also suggested that phytoene synthase from tomato is a peripheral plastid membrane protein [4] or periferally associated with thylakoid membranes [22].…”

Expression of a phytoene synthase gene and characteristic carotenoid accumulation during citrus fruit development

“…They suggested that the most probable cleavage site for the MEL5 is after or near the 83rd amino acid, which corresponds to the 90th amino acid in our CitPSY1. Although there has been no available protein information on citrus PSY, the position of the 90th amino acid is based on the estimated size of tomato PSY (Bartley et al 1992; Lawrence et al 1993; Fraser et al 1994). However, taking into consideration that the size of mature polypeptides were predicted based on comparisons with the bacterial (33.0 kDa) and cyanobacterial (35.7 kDa) orthologs of PSY (Chamovitz et al 1992), the possibility can not be excluded that the location of the cleavage site might be at the 153rd amino acid or at another site at around the 125th amino acid.…”

The use of transgenic and naturally occurring mutants to understand and manipulate tomato fruit ripening

“…• Several ripening-related cDNAs have homology to cloned mRNAs which also accumulate during stressrelated processes. TOM 66, TOM 111 and TOM 129 are homologous to low molecular weight heat shock proteins (Fray, Lycett & Grierson 1990;Lawrence, Cline & Moore 1993;Picton et al 1993a respectively). It is not known why these genes are active during fruit ripening.…”