Genome Sequencing and Preliminary Assembly of Tung Tree (Vernicia fordii)

Tung tree (Vernicia fordii) is an economically important non-edible woody oil tree originated in China. It is mainly distributed in subtropical areas of China and used to produce tung oil for centuries. Argentina, Africa, Paraguay and the United States have introduced and cultivated the tree. Tung tree seeds contain 50-60% oil with about 80 mole α-eleostearic acid (9cis, 11trans, 13trans octadecatrienoic acid). Because of the three special conjugated double bonds in eleostearic acid, tung oil is easily oxidized and forms a unique polymer after being exposed to air, to form a tough, glossy, waterproof, insulative and anticorrosive surface on the object it is coating. Tung oil is widely used in paints, varnishes, coatings and finishes due to these excellent properties. Tung oil is also a high-quality raw material for producing biodiesel and composite functional material. Besides, tung tree is an important ornamental plant with bright-color flowers before leaves. The objective of this study was to sequence the tung tree genome. We obtained the low heterozygosity tung tree plant from inbred lines through SSR marker selection. DNA libraries with different insertion fragments (180bp, 500bp, 800bp, 3Kb, 10Kb, 15Kb, 20Kb) were constructed from the tung tree genome. These fragments were sequenced at both ends using paired-end sequencing method by Illumina Hiseq 2000. PacBio library was constructed and sequenced by third generation sequencing. The Aleurites cordata Thunb., male and female plant of Vernicia montana, close relatives of Vernicia fordii, were used for resequencing of the genomes. We obtained the whole genome sequencing data followed by assembly and bioinformation analysis. The total amount of genome sequencing was 326.60G with a coverage of 249.46X. Preliminary analysis showed that the tung tree genome was 1.3G, not heterozygous but contained highly duplicated sequences. We obtained the preliminary assembly result with 60.6K of Contig N50 and 803.8K of scaffolds. Total length of the assembled sequence was 1.12G, approximately 85% of the predicted genome size. Transcriptome data were used to assess the genome data. The results showed that the coverage of unigenes was 94.97% and matching rate of reads achieved 88.3-95.6%. These data indicate that the assemble result of the tung tree genome is of high integrity. This study provides fundamental information for evaluating GC distribution and sequencing depth distribution, annotating genes, and analyzing evolution and biological functions in subsequent studies. Specified This work was supported by the projects of state forestry research and public service industry (201204403).