Morphological and metabolic changes in Changshan Huyou (Citrus aurantium) following natural tetraploidization
Polyploids in citrus are generally used to improve crop varieties. Changshan Huyou (Citrus aurantium) is a native citrus species in China that is highly adaptable and has pharmaceutical value. In this study, we evaluated phenotypic variations and metabolic alterations following autotetraploidization of Changshan Huyou seedlings and fruits and analyzed the associated transcriptomic changes. Tetraploid seedlings had rounder and thicker leaves, larger floral organs and fruits, and satisfactory viability of pollen grains and ovules.The tetraploid fruits accumulated lower levels of soluble solids but similar levels of organic acids.Metabolic profiling of three tissues of fruits revealed that most differentially accumulated metabolites (DAMs),including flavonoids, lignans, and coumarins, were downregulated. In contrast, the upregulated DAMs mainlyincluded alkaloids, amino acids, and terpenoids in tetraploid peels, as well as, flavonoids and organic acids injuice sacs. Genes that were upregulated in expression were associated with phenylpropanoid biosynthesis,secondary metabolite biosynthesis, and the biosynthesis of various alkaloid pathways. The results of Pearsoncorrelation analysis showed that the upregulated genes that encoded peroxidase and cytochrome P450 wereclosely related to a higher accumulation of amino acids and alkaloids in tetraploid peels, and neohesperidin andquercetin glucoside were increased by F5H, CYP450 81Q32, F3'H, 4CL, and UFOG, as well as, some transcriptionfactors in tetraploid juice sacs. These findings indicated that tetraploids may be used in breeding triploid citrus,especially seedless varieties, and for pharmaceutical purposes in fruit processing, as they influence metabolitesfollowing polyploidization.