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Scientia Silvae Sinicae ›› 2015, Vol. 51 ›› Issue (3): 41-48.doi: 10.11707/j.1001-7488.20150306

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Identification of α-Linolenic Acid Metabolism Pathway Based on Transcriptome Data of Vernicia fordii Kernels during Tung Oil Synthesis Stage

Chen Hao, Tan Xiaofeng   

  1. Key Laboratory of Cultivation and Protection for Non-Wood Forest Trees of Ministry of Education Key Laboratory of Non-Wood Forest Products of State Forestry Administration Central South University of Forestry and Technology Changsha 410004
  • Received:2014-07-21 Revised:2014-08-22 Online:2015-03-25 Published:2015-04-10

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Abstract:

【Objective】 Tung oil extracted from tung tree (Vernicia fordii) kernels has extremely high economic value. Tung oil contains α-eleostearic acid up to 70 percent. However, there are some difficulties in screening enzyme genes involved in α-eleostearic acid metabolism of tung tree due to very few studies being carried out on plant α-eleostearic acid metabolism pathway. Studies on metabolism pathway of α-linolenic acid, the isomers of α-eleostearic acid, were more in-depth and provide an example for analyses of metabolism pathway of α-eleostearic acid. This study was aimed to provide a theoretical basis for explaining the mechanism of α-eleostearic acid metabolism of tung tree through identifying α-linolenic acid metabolism pathway based on transcriptome data of tung tree kernels. It was also intended to largely accelerate the processes of genetic improvement and molecular breeding of tung tree through regulating gene expression profiles and developing molecular markers tightly linked to them. 【Method】 This study compared transcriptomes of tung tree kernels of 3 different oil synthesis stages using RNA-Seq technology and subsequently obtained a lot of differentially expressed Unigenes which can be classified into 128 metabolic pathways. Through GO classification and pathway enrichment analysis, the metabolism pathway of α-linolenic acid was identified and the expression profiles of related genes were analyzed. 【Result】 A total of 58 439 non-redundant Unigene with a 200-3 000 nucleotide-length were identified by RNA-Seq of tung tree kernel RNA of stages I-III. Accounting for 70.3 percentage of all non-redundant Unigenes, a total of 41 059 Unigene sequences could be matched to public database. Non-redundant Unigenes with different sequence length possessed different matching efficiency in alignments against sequences obtained from database. The longer the sequence was, the higher the matching efficiency would be. The matching efficiency of sequences with length greater than 2 000 bp was up to 98.28% whereas the matching efficiency of sequences with 500-1 000 bp and 100-500 bp length was decreased to 78.86% and 48.99%, respectively. Accounting for 0.47 percentages of all non-redundant Unigenes, a total of 105 Unigenes in 3 transcriptome data were enriched into α-linolenic acid metabolism pathway. Each pair-wise comparison of 3 transriptome data identified numbers of differentially expressed Unigenes and some of them were involved in α-linolenic acid metabolism pathway. Through alignment against KEGG database, 105 Unigene sequences were found to correspond to fourteen key enzyme genes involved in α-linolenic acid metabolism. These key enzyme genes were observed to have homologous genes in other species. Expression profiles showed that genes related to anabolism were generally up-regulated whereas genes related to catabolism were generally down-regulated during oil synthesis stage. 【Conclusion】 This study elucidated α-linolenic acid metabolism pathway of tung tree based on its kernel transcriptome data. Furthermore, key enzyme genes involved in α-linolenic acid metabolism were identified and their expression profiles were analyzed. The results of this study play important roles in enlightenment of the follow-up studies.

Key words: Vernicia fordii, transcriptome sequencing, α-linolenic acid metabolism, gene expression profiles

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