High-temperature stress alters cuticular wax metabolism and epidermal morphology in relation to the dull appearance in banana fruit.

Banana fruit ripening is highly temperature-sensitive. This study compared fruit surface morphology, cuticular wax composition, and the expression of wax metabolism-related genes at 20 °C and 30 °C. Bananas stored at 30 °C developed surface dulling, accompanied by slower chlorophyll degradation, lower lightness, and reduced chroma. High-temperature stress caused pronounced concave deformation of epidermal cells, which normally form plateau-like nano-ridges. Although total cuticular wax load remained stable, compositional shifts were observed at 30 °C, including decreased very-long-chain n-alkanes and increased sterols. Among 83 differentially expressed genes involved in surface lipid metabolism, MaKCS11 and MaCER3,which arekey genes for very-long-chain fatty acids and n-alkane biosynthesis, were down-regulated by high temperature. Furthermore, transcription factors MaMYB39 and MaMYB108 were differentially expressed and correlated with MaKCS11 and MaCER3. Collectively, these results establish a link between altered cuticular wax metabolism and the dull appearance of banana fruit during high-temperature ripening.