Use of genomics tools to isolate key ripening genes and analyse fruit maturation in tomato.

Development, maturation and ripening of fruits has received considerable experimental attention, primarily due to the uniqueness of such processes to plant species and the importance of fruit as a significant aspect of human dietary intake and nutrition. Molecular and genetic analysis of fruit development, and especially ripening of fleshy fruits, has resulted in significant gains in knowledge over recent years, especially with respect to understanding ethylene biosynthesis and response, cell wall metabolism and, to a lesser extent, environmental cues which impact ripening. Tomato has proved to be an excellent model system for the analysis of fruit ripening and development, in part due to the availability of well characterized ripening mutants. Especially interesting are the non-allelic ripening-inhibitor (rin) and non-ripening (nor) mutations which result in non-ripening fruit. Fruit from both mutants are deficient in climacteric respiration and the associated burst in ethylene biosynthesis. Exogenous ethylene does not restore ripening yet does induce expression of ethylene-regulated ripening genes, suggesting both mutations block necessary aspects of ripening outside the realm of ethylene's influence. Both mutations therefore represent genes upstream of ethylene control and additional non-ethylene mediated aspects of ripening. Both genes have recently been isolated through positional cloning strategies and it was shown that ripening is regulated, in part, by a MADS-box transcription factor at the rin locus. Recent development of tools for tomato genomics summarized here have further expanded the potential of the tomato system for the elucidation of genetic regulatory components impacting fruit development, ripening and nutritional quality.