Genetic Analysis of Fruit Ripening and Quality in Tomato

Fleshy fruits have a dual function in the reproductive strategies of plants. Initially, fleshy fruits protect developing seed from predation and then, once the seeds are mature, they facilitate dispersal to complete the plants reproductive cycle. Plants have evolved numerous chemical and physical barriers that discourage seed predation from fleshy fruits. Similarly, the ripening of fleshy fruits occurs through a range of coordinated biochemical processes that convert an unpalatable unripe fruit into a fruit that is nutritious and desirable to seed dispersing fauna. The biochemical changes that occur at the onset of ripening are species specific but several general processes occur that are common to many fruits, suggesting that the mechanisms that control ripening may be evolutionarily conserved. For example, fruit ripening is often accompanied by the accumulation of brightly colored pigments, the synthesis of aroma volatiles and the conversion of complex carbohydrates into sugars. These changes facilitate seed dispersal strategies. We have taken a forward genetics based approach to identify genes involved in determining fruit ripening and quality in tomato. Several genes have been cloned including GREEN-RIPE which alters ethylene responsiveness, GREEN-FLESH which is required for chlorophyll degradation and LUTESCENT 2 which is required for normal plastid development and alters ripening time in tomato. Other loci that alter various aspects of fruit quality including cuticle composition and color development are currently being characterized and mapped with a view to identifying the underlying genes. Progress on these efforts will be presented.