Changes in expression of carotenoid and chlorophyll metabolic genes during regreening process in citrus fruit
Nichapat Keawmanee is a Ph.D. student in the Science of Biological Production, United Graduate School of Agricultural Science, Shizuoka University, Japan, under the supervision of Prof. Masaya Kato. Her recent research focused on the changes of pigment profiles in citrus during the fruit regreening process. Citrus fruit ripen from green to orange during the winter season. When the fruit remains on the tree late into the spring or summer season, the fruit skin color will reverse from orange to green. This is particularly visible for Valencia oranges. The occurrence of the regreening process is related to the accumulation of pigments such as chlorophylls and carotenoids in the fruit skin. In a previous study, researchers found that temperature, light, nitrogen fertilizer, and plant hormones induced the regreening process. However, the mechanism of regreening remains unknown. The objective of this study was to determine the chlorophyll and carotenoid content and related gene expression in Valencia orange skin during fruit regreening. During the regreening process, the color of skin reversed from orange to green accompanied by a decrease of the carotenoids content and accumulation of chlorophyll. In addition, the occurrence of green color was more obvious in the stem end than in other areas. Changes of pigment profiles were regulated by the expression of chlorophyll and carotenoid metabolism genes. The up-regulation of chlorophyll biosynthetic genes and the down-regulation of chlorophyll degradation genes contributed to increased chlorophyll content. Meanwhile, the down-regulation of carotenoid biosynthetic genes led to the decrease of carotenoid content. These results suggested that the regreening process of citrus fruit was regulated by promoting the chlorophyll biosynthetic genes, and repressing the chlorophyll degradation and carotenoid biosynthetic genes. Further work will study the effect of exogenous gibberellins on pigment profile during the regreening process. The expression of genes being associated with pigment accumulation is still unknown. We hope that this research might help gain a deeper insight into the role of phytohormones in regulating the pigment profiles during the regreening.
Nichapat Keawmanee won the ISHS Young Minds Award for the best poster presentation at the V Asia Symposium on Quality Management in Postharvest Systems in Thailand in December 2021.
Nichapat Keawmanee, Department of Bioresource Sciences, Faculty of Agriculture, Shizuoka University, 836 Ohya, Suruga, Shizuoka 422-8529, Japan, e-mail: email@example.com
The article is available in Chronica Horticulturae