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Title: Fatty acid profile and Unigene-derived simple sequence repeat markers in tung tree (Vernicia fordii)

Author
item ZHANG, LIN - Central South University Of Forestry And Technology
item JIA, BAOGUANG - Central South University Of Forestry And Technology
item TAN, XIAOFENG - Central South University Of Forestry And Technology
item THAMMINA, CHANDRA - University Of Connecticut
item LONG, HONGXU - Central South University Of Forestry And Technology
item LIU, MIN - Central South University Of Forestry And Technology
item WEN, SHANNA - Central South University Of Forestry And Technology
item SONG, XIANLIANG - Shandong Agricultural University
item Cao, Heping

Submitted to: PLoS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2014
Publication Date: 8/28/2014
Publication URL: http://handle.nal.usda.gov/10113/59560
Citation: Zhang, L., Jia, B., Tan, X., Thammina, C.S., Long, H., Liu, M., Wen, S., Song, X., Cao, H. 2014. Fatty acid profile and Unigene-derived simple sequence repeat markers in tung tree (Vernicia fordii). PLoS One. 9(8):e105298. https://doi.org/10.1371/journal.pone.0105298.
DOI: https://doi.org/10.1371/journal.pone.0105298

Interpretive Summary: Tung tree or tung oil tree (Vernicia fordii) is a native woody oil plant in subtropical areas of China. This important tree has been grown in China for the production of tung oil for centuries. Tung tree was introduced to the United States in 1904 and grown mainly in the South regions of the United States. Dried tung oil is impervious to heat, moisture, dust and many chemical challenges. Tung oil, unlike other drying oils, does not darken with age. These properties of tung oil make it a widely used drying ingredient in paints, varnishes, coatings and finishes. Recently, tung oil has been explored as a raw material to produce biodiesel, polyurethane and wood flour composites, thermosetting polymer and repairing agent for self-healing epoxy coatings. Major efforts have been directed at understanding the genetic control of tung oil biosynthesis. Many tung oil biosynthetic genes have been identified. The expression of some tung genes has been studied by northern blotting, quantitative real-time PCR and western blotting. A few tung proteins have been expressed in heterologous systems including E. coli, fungi and Arabidopsis. However, selection of target genes for genetic engineering of plant oils is difficult because oil is biosynthesized by at least 10 enzymatic steps and each step is catalyzed by multiple isozymes. Furthermore, it has been difficult to study tung oil biosynthesis at the protein level because these enzymes are mostly hydrophobic and membrane-localized proteins. Understanding fatty acid composition and genetic diversity among tung tree germplasm resources is essential for tung tree breeding and clonal improvement. We evaluated fatty acid profiles, characterize microsatellites and develop unigene-derived SSR markers in 41 tung tree accessions collected from 5 Provinces in China. Gas-chromatography analyzed fatty acid profiles in the mature seeds. We utilized Illumina platform-based transcriptome sequencing of cDNA library from developing tung seeds and characterized microsatellites from the transcriptome sequences and developed 15 new polymorphic genic-SSR markers. The novel genic-SSR markers will provide a useful tool for genetic research and comparative genome analysis in tung tree. The lipid profiles of the seeds from 41 tung tree accessions will be valuable for biochemical and breeding studies.

Technical Abstract: Tung tree (Vernicia fordii) provides the sole source of tung oil widely used in industry. Lack of fatty acid composition and molecular markers hinders biochemical, genetic and breeding research. The objectives of this study were to determine fatty acid profiles and develop unigene-derived simple sequence repeat (SSR) markers in tung tree. Fatty acid profiles of 41 accessions showed that the ratio of a-eleostearic acid was increasing continuously with a parallel trend to the amount of tung oil accumulation while the ratios of other fatty acids are decreasing in different stages of the seeds and that a-eleostearic acid (18:3) consisted of 77% of the total fatty acids in tung oil. Transcriptome sequencing identified 81,805 unigenes from tung cDNA library constructed using seed mRNA and discovered 6,366 SSRs in 5,404 unigenes. The di- and tri-nucleotide microsatellites accounted for 92% of the SSRs with AG/CT and AAG/CTT being the most abundant SSR motifs. Fifteen polymorphic genic-SSR markers were developed from 98 unigene loci tested in 41 cultivated tung accessions by agarose gel and capillary electrophoresis. Genbank database search identified 10 of them putatively coding for functional proteins. Quantitative PCR demonstrated that all 15 polymorphic SSR-associated unigenes were expressed in tung seeds and some of them were highly correlated with oil composition in the seeds. Dendrogram revealed that most of the 41 accessions were clustered according to the geographic region. These new polymorphic genic-SSR markers will facilitate future studies on genetic diversity, molecular fingerprinting, comparative genomics and genetic mapping in tung tree. The lipid profiles in the seeds of 41 tung accessions will be valuable for biochemical and breeding studies.