Biochemical, transcriptome and metabolome analysis of the pulp of Citrus sinensis (L.) Osbeck ‘Hong Jiang’ and its two variants reveal pathways regulating pulp taste, mastication, and color

Abstract

Background: Hong Jiang (HC), a grafted chimera of sweet orange (Citrus sinensis (L.) Osbeck), is prone to variations in fruit shape, taste, and pulp mastication. We studied the transcriptomes and metabolomes pf pulps of HC and its two variants (CB: fruits with changed pulp mastication, taste, and color and JB: fruits with changed pulp color and taste) to explore the related pathways.

Results: JB accumulated higher organic acids as compared to HC and CB. Flavonoid content was highest in HC followed by JB and CB. The soluble sugar content was lower, while cellulose content was higher in both JB and CB as compared to HC. We found 5,156 and 1,673 DEGs and 283 and 94 DAMs in HC vs JB and HC vs CB, respectively. The differential regulation of starch and sucrose metabolism, galactose metabolism, glycolysis/gluconeogenesis, fructose and mannose metabolism, and citrate cycle pathways could be associated with changes in sugar contents and tastes in JB and CB. Cell-wall polymer-related DEGs/DAMs were associated with the inferior mastication quality of JB and CB. Carotenoid biosynthesis possibly imparts yellowish and reddish pulp color in HC. Additional to this pathway, the anthocyanin biosynthesis led to the changes in JB and CB pulp color.

Conclusions: This combined methodological approach proved to be useful in delineating the large-scale changes in the transcripts and metabolites of variant fruits in a chimeric citrus variety. This study provides advanced and large-scale data on citrus taste, mastication, and pulp color.