Lycopene cyclases determine high α-/β-carotene ratio and increased carotenoids in bananas ripening at high temperatures

Bananas are a recommended food source to alleviate vitamin A deficiency because they contain a high ratio of provitamin A precursors. The objective of this study was to investigate carotenoid accumulation pattern in banana fruits during postharvest ripening and the mechanisms regulating this process. Ripe banana pulp had an unusually high alpha-/beta-carotene ratio (1.05), and the carotenoid contents increased (p <= 0.05) under light and high temperature. We analyzed the sequences, transcript levels, and functions of genes involved in carotenoid synthesis. The high ratio of alpha-/beta-carotene in ripe banana fruit was explained by the high flux to the a-carotene biosynthetic pathway, as reflected by high transcript levels of LCYE, and the weak flux to the beta-carotene branch of the biosynthetic pathway due to inactive MaLCYB1.2. High temperature during ripening up-regulated the transcript levels of genes involved in the alpha- and beta-carotene biosynthesis pathways and the activities of their encoded enzymes.