Differential regulation of red light- and ethephon-induced degreening in postharvest kumquat fruit

Peel color is closely associated with the commercial value of citrus fruit. In early market or tropical regions, citrus fruit often show non-uniform coloration, which requires degreening practice at post-harvest stage. Here, we studied the degreening effect of red LED light, ethephon, and their combination treatment on kumquat fruit. Both red LED light and ethephon promoted fruit degreening, causing ultrastructural changes of chloroplasts accompanied by chlorophyll degradation. Transcriptome analysis revealed metabolic reprogramming in chloroplasts but the way how genes responded to red LED light and ethephon were remarkably different. Transient expression in Nicotiana benthamiana suggested that FcrCLH, FcrPPH and FcrSGR genes were potentially key factors in regulation of fruit degreening. Furthermore, red LED light promoted the catabolism of chloroplast components in vitro. This study provides novel insights into the molecular mechanism of fruit degreening and unravels an efficient practice for future post-harvest management of citrus fruit.