Morphological and metabolic changes in Changshan Huyou (Citrus changshan-huyou) following natural tetraploidization

Polyploids in citrus are generally used to improve crop varieties. Changshan Huyou (Citrus changshan-huyou) 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 adult tetraploid scions of Changshan Huyou with contemporary diploid scions as the control in the phenotypic variations, metabolic alterations of fruits and associated transcriptomic changes.

The tetraploid scions 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. Pearson Correlation Analysis showed that the upregulated genes encoding PEROXIDASE and CYTOCHROME P450 (CYP450) were closely related to the higher accumulation of amino acids and alkaloids in tetraploid peels, and up-regulated neohesperidin and quercetin glucoside were positively associated with FERULATE-5-HYDROXYLASE (F5H), CYP450 81Q32, FLAVONOID 3'-MONOOXYGENASE (F3'H), 4-COUMARATE-CoA LIGASE 1 (4CL1), and UDP-GLUCOSE FLAVONOID 3-O-GLUCOSYLTRANSFERASE (UFOG), as well as, some transcription factors in tetraploid juice sacs.

The tetraploid Changshan Huyou investigated here may be used in triploids breeding to produce seedless citrus, and for fruit processing on pharmaceutical purpose due to the alteration of metabolites following polyploidization.