Abstract
To elucidate the mechanism underlying special characteristic differences between a spontaneous seedling mutant ‘Huapi’ kumquat (HP) and its wild-type ‘Rongan’ kumquat (RA), the fruit quality, metabolic profiles, and gene expressions of the peel and flesh were comprehensively analyzed. Compared with RA, HP fruit has distinctive phenotypes such as glossy peel, light color, and few amounts of oil glands. Interestingly, HP also accumulated higher flavonoid (approximately 4.1-fold changes) than RA. Based on metabolomics analysis, we identified 201 differential compounds, including 65 flavonoids and 37 lipids. Most of the differential flavonoids were glycosylated by hexoside and accumulated higher contents in the peel but lower in the flesh of HP than those of RA fruit. For differential lipids, most of them belonged to lysophosphatidycholines (LysoPCs) and lysophosphatidylethanolamines (LysoPEs) and exhibited low abundance in both peel and flesh of HP fruit. In addition, structural genes associated with the flavonoid and lipid pathways were differentially regulated between the two kumquat varieties. Gene expression analysis also revealed the significant roles of UDP-glycosyltransferase (UGT) and phospholipase genes in flavonoid and glycerophospholipid metabolisms, respectively. These findings provide valuable information for interpreting the mutation mechanism of HP kumquat.
Highlights
Kumquat is of the genus Fortunella that is closely related to Citrus genus
We previously found that the contents of organic acid and soluble sugar and the expression levels of related genes exhibited large differences between Huapi’ kumquat (HP) and RA fruits (Wei et al, 2021)
Color indexes, including L∗, a∗, b∗, and citrus color index (CCI), showed no difference between HP and RA during the development stage of 60∼150 days after flowering (DAF), but were significantly lower in HP compared to RA during the turning and maturation stage (150–180 DAF) (Supplementary Figure 1)
Summary
Kumquat is of the genus Fortunella that is closely related to Citrus genus. As an important part of the most popular fruit crops of citrus, kumquat is widely distributed and cultivated in the world, in southeast China. It is a favorite by consumers due to its good taste, small size, and being eaten raw without peeling. Besides its attractive organoleptic properties, kumquat is an excellent source of nutrients and phytochemicals, such as flavonoids, phenolic acids, carotenoids, vitamins, polysaccharides, Flavonoid and Lipid in Kumquat essential oil, lipids, and dietary fiber (Liu et al, 2019) It is an important herbal medicine in Chinese traditional medicine. Revealing the constitution and biosynthesis of functional compounds in kumquat fruit will benefit for citrus breeding to produce new resources of functional fruit
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