Ethylene in fruits: beyond ripening control

Fruits are a rich source of nutrients, minerals, and dietary fibers for both humans and animals. While the gaseous phytohormone ethylene is well-known for its role in controlling fruit ripening, there is growing evidence that ethylene also plays crucial roles in regulating other developmental processes of fruits, such as sex determination, fruit set, and fruit growth. In this review, we aim to revisit these findings from various species like cucumber, melon, tomato, rice, maize, and more. These studies not only enhance our understanding of ethylene's function in fruits but also highlight the potential for manipulating ethylene to improve crops. Furthermore, we discuss recent studies that show the ethylene precursor ACC (1-AMINOCYCLOPROPANE-1-CARBOXYLATE), and the ethylene signaling components EIN2 (ETHYLENE INSENSITIVE2) and EIN3 (ETHYLENE INSENSITIVE3) have ethylene-independent function in specific conditions. This phenomenon, combined with findings of dosage-dependent ethylene functions in certain conditions, highlights the importance of analyzing mutants with completely blocked ethylene pathways in different species at specific developmental stages and tissue types. Overall, this review offers a timely and essential summary of ethylene's role in sex determination, fruit formation, and fruit growth, which could be beneficial for horticulture crop breeding.