Transcriptome Sequencing Reveals Fatty Acid Synthesis Pathway in Eucommia ulmoides Oliv.

Eucommia ulmoides Oliv. is one of the important economic and medicinal plants in China. E.ulmoides  oil; extracted from the kernels; contains high content of α-linolenic acid which ranges from 38.7% to 67.6%. Past researches on E.ulmoides were mainly focused on the cultivation and conventional breeding of the tree. However the molecular mechanism related to fatty acid synthesis pathway in E.ulmoides’s kernel is still uncovered. The objective of this study was to generate information for better understanding of fatty acid biosynthesis by transcriptomic analyses. Transcriptome sequencing was conducted on kernels of 60 and 150 DAF (days after flowering) in varieties ‘HuaZhong No.10’ and ‘HuaZhong No.6’. De novo assembly generated a total of 96469 unigenes with an average length of 690 bp. Among them, 49856 unigenes accounted for 51.68% of all-unigene were annotated against NR (non-redundant), GO (Gene Ontology) and COG (Clusters of Orthologous Groups) databases, 38983 unigenes were assigned 3 categories and 56 branches by comparing with CO database, and 20699 unigenes were assigned 25 categories with COG database. In addition, 11975 unigenes identified by functional annotation against KEGG (Kyoto Encyclopedia of Genes and Genomes) database were mapped to 117 metabolic pathways. The real- time quantitative RT-PCR (qPCR) analysis showed that the expression levels of 10 fatty acid synthesis–related unigenes (fabG, accA, fabZ, fabF, FATB, fabI, FATA, ACAC, fabD, accB) gradually declined in 150 DAF kernels compared to 60 DAF kernels from ‘HuaZhong No. 10’ and ‘HuaZhong No. 6’. qPCR also showed that the expression levels of these genes in 60 DAF kernels from ‘HuaZhong No. 10’ were significantly higher than those from ‘HuaZhong No. 6’. The expression profiles of the 10 genes were in agreement with the transcriptome data in the developing kernels of E. ulmoides. This study provides an important foundation for further characterizing the functional genes involved in the process of seed development in E. ulmoides.