Cytokinin, gibberellin and auxin regulate parthenocarpy in cucumber via modulating downstream auxin signaling network

Parthenocarpy, the development of fruit without pollination and fertilization, provides a solution for ensuring yield stability in adverse environmental conditions. The application of phytohormones in inducing parthenocarpic fruits is an important strategy for horticulture fruit production; however, its inner physiological and molecular mechanisms are less understood. Here, we investigated the hormonal regulation of parthenocarpic fruit formation in cucumber. Auxin, gibberellic acid (GA), and cytokinin treatments successfully induced fruit formation in cucumber. Significant increase in cell size began 1 day after anthesis, indicating that 1 day after anthesis is the critical stage for fruit set. Inner indole-3-acetic acid (IAA) and GA levels were enhanced in parthenocarpic fruit, while no significant changes were observed in cytokinin, abscisic acid, salicylic acid, and jasmonic acid levels. Hormone-induced parthenocarpic fruit showed elevated expression of both auxin signaling and GA biosynthesis genes, and inhibited levels of ABA signaling genes. These findings indicate that auxin and GA play central roles in parthenocarpic fruit formation. These findings also reveal the possibility of improving fruit parthenocarpy through gene editing of auxin signaling and GA biosynthesis genes.