Gibberellin-dependent pulp pigmentation in CPPU-induced parthenocarpic melon fruit: Insights from metabolome and transcriptome analysis

The plant growth regulator N-(2‑chloro-4-pyridyl)-N′-phenylurea (CPPU) is applied to induce parthenocarpic fruit setting in melon (Cucumis melo L.) production. However, CPPU-induced fruits frequently exhibit a decline in quality attributes, such as sucrose, aroma, and pigmentation, the mechanisms underlying these changes remain largely unclear. This research assessed the effects of CPPU application on carotenoid biosynthesis in the pulp during melon fruit development, aiming to elucidate the underlying mechanisms. Transcriptome and metabolome analyses were employed to examine changes in pigment and hormone levels in melon fruit at various developmental stages following CPPU treatment. The results indicated that CPPU application for fruit setting significantly reduced β-carotene content in the fruit pulp compared to fruits resulting from artificial pollination. Transcriptome analysis revealed a decrease in the expression of carotenoid biosynthesis genes (e.g., PSY1/2, Z-ISO, and LYCB), while the expression of catabolic enzyme genes (e.g., NCED5/6, NXS, and CCD4) were up-regulated following CPPU application. Metabolome analysis showed a decrease in gibberellin production during the development of CPPU-induced fruits compared to pollinated samples. Furthermore, exogenous gibberellin application recovered the pigment defects in the CPPU-induced parthenocarpic fruits. This study provides novel insights into how CPPU-induced parthenocarpy affects melon pulp pigmentation during development, offering valuable theoretical foundations for improving fruit set management in melon cultivation.