THE USE OF TRANSGENIC AND NATURALLY-OCCURRING MUTANTS TO UNDERSTAND AND MANIPULATE TOMATO FRUIT RIPENING

In the years since we last reviewed the use of mutants to study tomato fruit ripening (Grierson et al. 1987), considerable information has been gained by the cloning, sequencing and identification of many mRNAs implicated in this developmental process. Genes involved in cell wall degradation, colour change and ethylene synthesis have been cloned, and antisense techniques have been developed and used to produce genetically engineered mutant fruit deficient in these aspects of ripening (see Gray et al. 1992). Recently, a previously cloned ripening gene has been used to complement a naturally occurring fruit colour mutant, yellow flesh (Fray and Grierson 1993a), and a ripening impaired mutant, ripening inhibitor, has been used to identify several new ripening-related mRNAs (Picton et al. 1993b). The chromosomal region bearing the ripening inhibitor mutation has been subjected to high-resolution mapping (Churchill, Giovannoni and Tanksley 1993) and chromosome walking experiments are in progress to identify this gene.