Diverse actions of auxin on fruit development and ripening

Abstract The process of fruit development involves the initiation of fruit set, followed by growth, maturation, and ripening. Auxin, a key plant hormone, regulates nearly all aspects of plant growth and development. In concert with gibberellic acid (GA), auxin promotes cell division and expansion, crucially influencing fruit initiation and growth post-fertilization. Fruit ripening is a multifaceted process. While ethylene remains the dominant phytohormone in climacteric fruits, recent research highlights the increasing role of auxin. Although auxin inhibits the climacteric ripening of fruits like tomatoes, emerging studies suggest its stimulatory role in the ripening of other climacteric fruits, such as apples and peaches. This review examines auxin's involvement in the development of reproductive organs, fruit initiation and growth, ripening, shaping, and abscission, emphasizing its distinct regulatory effects in climacteric fruits. Furthermore, it explores potential molecular mechanisms and highlights future research avenues focused on auxin's role in fruit development and ripening.