Morphological and metabolic changes in Changshan Huyou (Citrus aurantium) following natural tetraploidization

Abstract Background 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. However, the influence in Changshan Huyou following polyploidization remains unclear. Here we evaluated the phenotypic variations and metabolic alterations following autotetraploidization of Changshan Huyou seedlings and fruits and analyzed the associated transcriptomic changes. Result The 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 of 2064 differentially accumulated metabolites (DAMs), including flavonoids, lignans, and coumarins, were downregulated. In contrast, the upregulated DAMs mainly included alkaloids (clausine K and 2-(1-pentenyl)quinoline), amino acids (L-asparagine and L-ornithine), and terpenoids (deacetylnomilin and evodol) in tetraploid peels, as well as, flavonoids (neohesperidin and quercetin-5-O-β-D-glucoside) and organic acids (2-methylsuccinic acid and dimethylmalonic acid) in juice sacs. The upregulated genes were associated with phenylpropanoid biosynthesis, secondary metabolite biosynthesis, and the biosynthesis of various alkaloid pathways. The results of Pearson correlation analysis showed that the upregulated genes that encoded peroxidase and cytochrome P450 were closely related to a higher accumulation of amino acids and alkaloids in tetraploid peels, and neohesperidin and quercetin glucoside were increased by ferulate-5-hydroxylase, CYP450 81Q32, flavonoid 3'-monooxygenase, 4-coumarate–CoA ligase 1, and UDP-glucose flavonoid 3-O-glucosyltransferase, as well as, some transcription factors in tetraploid juice sacs. Conclusion The tetraploid Changshan Huyou investigated here may be used in breeding triploid citrus, especially to produce seedless varieties, and for pharmaceutical purposes in fruit processing, as they influence metabolites following polyploidization.