Allopolyploids are known to have superior advantages such as high growth speed. Triploids have even greater heterozygosity, explaining more phenotypic variance than 2n hybrid F1 and have therefore become new resources in breeding. To date, the metabolomic basis underlying polyploidization vigor remains unclear. Here, we identified and compared 235 metabolites in the shoot apical buds between multiple allo-triploid populations and parental 2n hybrid F1 in Populus via metabolome profiling using liquid chromatography-mass spectrometry (LC-MS) assays. Associations with growth vigor in three types of allo-triploid populations, namely first division restitution (FDR), second division restitution (SDR) and postmeiotic restitution (PMR) generated from doubled 2n female gametes and male gametes of 2n hybrid, were also investigated. Each allo-triploid population has different sub-genome duplicated. Major metabolomes were amino acids, secondary metabolism associated, and carbohydrates. We mapped 181 metabolites into known metabolism pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG). Ten compounds, i.e., fructose 1,6-diphosphate and xylulose, were more abundant in all allo-triploids than the 2n hybrid. Principal component analysis revealed the abundance of metabolites fell into distinct clusters corresponding to ploidy composition. Heterozygosity in triploids mainly effected the contents of carbohydrates and secondary metabolites rather than lipids. Comparisons between subgroups with different growth rates revealed some carbohydrates and secondary metabolites of flavonoids were positively associated with gene expression and the high growth vigor. The results provided an informative metabolomic basis for factors conferring growth vigor in polyploid Populus. IntroductionPolyploid organisms have more than two sets of chromosomes; 30-80% of plant kingdom are polyploid. Many plant lineages show evidence of palaeopolyploidization in their genomes. Polyploid plants usually have larger cell size and faster growth, which are both agronomically preferred traits [1]. Polyploid breeding in plants, including synthesized polyploidization, has increased the rate of breeding in many crops and also in trees, such as Populus [2][3][4][5]. Polyploidization leads to a series of genomic, metabolomic, cellular and physiological changes. Typically, a reduction in genome size occurs after polyploidization, followed by neo-functionalization, sub-functionalization and gene product dosage balance, gene rearrangement, and epigenetic modification, which all drive the evolution and speciation [6]. Cell size is usually increased in polyploid plants likely due to a delayed cell division [5].

Correa carmen is considered important because of its considerable ornamental and economic value. The most striking characteristic of C. carmen flowers is their long winter-flowering period. In the present study, we generated the first complete C. carmen chloroplast genome sequence based on Illumina paired-end sequencing data. The entire chloroplast genome comprises a circular molecule with 156,759 bp that forms a quadripartite organization with two inverted repeats (26,981 bp) separated by large (84,887 bp) and small (17,910 bp) single copy sequences. The C. carmen genome includes 95 protein-coding genes, 31 transfer RNA genes, and eight Cheng S, et al. 2 Genetics and Molecular Research 16 (4): gmr16039815 ribosomal RNA genes. Additionally, the base composition of the genome is biased (30.38% A, 18.92% C, 19.63% G, and 31.07% T) with an overall GC content of 38.55%. The results of a phylogenetic analysis are consistent with the traditional taxonomic framework of the family Rutaceae, and C. carmen is closely related to Phellodendron amurense.

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