| Tung tree(Vernicia fordii)is a traditional woody oil tree species widely distributed in China.As the highest quality dry oil in the world,tung oil has been applied in electronic industry,advanced printing ink,synthetic resin,plastic industry,rubber industry and other chemical industries.Oil content and seed weight are important factors determining the yield of tung trees.The content of a-eleostearic acid and other fatty acids are important indicators for evaluating the quality of tung oil.In this paper,491 tung tree accessions were used as materials,phenotypic data such as kernel weight,oil content,a-eleostearic acid content and other fatty acids content were collected from 2015 to 2017.Seeds from two tung tree accessions with different oil content at different developmental stages were selected for RNA sequencing.Molecular mechanism of high and low oil content in seeds and a number of SNP molecular markers were developed using RNA sequencing data.Candidate gene association analysis was carried out and the main results were as follows:1.The phenotype database consists of seed weight,oil content and fatty acids composition in mature seeds of 491 tung tree accessions was constructed.The variation range of seed weight and oil conten in mature seeds is very wide in natural population,which may be related to the genetic diversity of tung tree germplasm resources.At the same time,there is a high positive correlation between seed weight and oil content,which can be used as an important index to evaluate the yield of tung trees.The a-EA content of tung trees is generally high,with an average percentage of 79.64%.This indicates that tung trees has an efficient system for a-EA synthesis,transportation and storage.The molecular mechanism of this system needs to be elucidated.2.The oil content of 12 tung trees at 11 stages of seed development was quantified continuously,and oil accumulation curves of seeds from tung trees with different oil content were drawn.The results showed that trees with an oil content of about 70%in the mature endosperms had comparably longer rapid oil accumulation period of 5 to 7 weeks,whereas trees with an oil content of about 50%in the mature endosperms had a shorter rapid oil accumulation period of 2 to 4 weeks.Trees with an oil content of about 60%in the mature endosperms had a middle rapid oil accumulation period of 4 to 6 weeks,except one only with 2 weeks of oil quick accumulation.We concluded that the extended period of accumulation should be associated with the high seed oil content at maturity.3.We selected two tung trees with the biggest difference in oil content for RNA sequencing,based on the oil content of the mature endosperm:Tree H had the highest oil content(about 70%)and Tree L had the lowest oil content(about 45%).The results showed that many genes involved in glycolysis,fatty acid synthesis and TAG assembly still kept high expression in the late period of seed oil accumulation for tree H only,while a large number of genes involved in fatty acid degradation kept high expression in the late stage of seed oil accumulation in tree L only,and three transcription factors related to fatty acid synthesis,PⅡ,LEC1 and LEC1-Like,kept high expression in tree H only.High expression was maintained in late accumulation stage.Differential expression of key genes in these pathways may be one of the molecular mechanisms responsible for the difference of oil content in tung trees at the late stage of oil accumulation.This study provides a new perspective for explaining the molecular mechanism of oil content in tung tree seeds and a new breeding strategy for improving oil content in plant seeds.4.19 tung trees with different oil content were used as materials to identify 70315 SNPs distributed in 15340 genes by RNA-seq.In order to further develop functional molecular markers affecting oil content and fatty acid composition of tung tree,we performed GO classification and KEGG enrichment analysis of genes containing SNPs.A total of 41009(57.7%)SNPs from 8958 genes were successfully matched to GO functional classification.2776 genes containing 11963 SNPs were annotated to 125 KEGG pathways.Among them,1096 SNPs were matched to GO classification genes related to lipid synthesis.1231 SNPs were located in KEGG pathway related to fatty acid synthesis.These SNPs are expected to be further developed to functional molecular markers.5.Twenty-one candidate SNPs were selected as condidate SNPs which may affect oil content and fatty acid composition.We genotyped the population consist of 374 tung trees by MassARRY mass spectrometry technology.The association between candidate genes and oil content was further analyzed by TASSEL software.Five significant association SNPs were obtained,among which S1775-155811,S303-214966 and S228-148503 were located in the 5’-UTR regions of VfPDAT2,VfLPAAT1 and VfPDH-α3,respectively.These SNPs were likely to affect oil accumulation at the regulatory level.In addition,S48-719107 and S228-148503 in VfPDH-α1 and VfPDH-α3 were significantly correlated with seed weight,which may be due to the significant correlation between oil content and seed weight.These results not only provide a theoretical basis for understanding the molecular mechanism of oil content in tung tree,but also provide a new idea for molecular improvement of woody oil tree species. |
PDF Full Text Request