Fruit development

From the scientific point of view, fruit development is seen as a genetically programmed process unique to plants that requires a complex network of interacting genes and signaling pathways. In fleshy fruit, it involves three distinct stages, namely, fruit set, fruit development, and fruit ripening.

The first phase of fruit development corresponds to fruit set and early growth characterized by active cell division. In the following phase, the fruit undergo a steady increase in size mostly due to cell expansion. The last phase corresponds to fruit ripening and is characterized by dramatic changes in colour, texture and taste that contribute to the buildup of the fruit sensory quality.

Ripening is the final developmental stage of reproductive organs in higher plants and once maturation is reached, the fruit structure alters significantly till complete decay leading to seed dispersal. The ripening process has received most attention from geneticists and breeders, as this important process activates a whole set of metabolic pathways that make the fruit attractive, desirable, and edible for consumers. The biochemical, molecular, physiological and structural modifications associated with ripening are tightly orchestrated at the genetic level enabling thecontrol of appearance, aroma, flavour and texture in a way that renders the fruit appealing to a variety of seed-dispersing organisms among which human. These physiological changes are also important because they determine the postharvest and processing potentialities of the fruits. It is well established that the changes that take place during fruit ripening are driven by the coordinated expression of ripening-related genes which encode enzymes mediating the biochemical and physiological changes underlying the ripening process. They also encode regulatory proteins involved in the activation of signaling pathways and transcriptional activities leading to the expression of key regulatory genes responsible for the triggering and coordination of the fruit ripening developmental program. Fruits can be divided into two groups according to the regulatory mechanisms underlying their ripening process. Climacteric fruit, such as tomato, apple, pear, and melon are characterized by a ripening-associated increase in respiration and in ethylene production, the phytohormone ethylene being the major trigger and coordinator of the ripening process. By contrast, non-climacteric fruits, such as grape, orange and pineapple, are characterized by the lack of ethylene-associated respiratory peak and the signaling pathways that drive the ripening process remain elusive. The identification of regulatory or structural genes controlling fruit development and ripening is a necessary step towards enlarging our understanding of the fruit biology and hence opening new leads for improving fruit quality traits.