Abstract
BackgroundThe persimmon Diospyros kaki Thunb. is an important commercial and deciduous fruit tree. The fruits have proanthocyanidin (PA) content of >25% of the dry weight and are astringent. PAs cause astringency that is often undesirable for human consumption; thus, the removal of astringency is an important practice in the persimmon industry. Soluble PAs can be converted to insoluble PAs by enclosing the fruit in a polyethylene bag containing diluted ethanol. The genomic resource development of the persimmon is delayed because of its large and complex genome. Second-generation sequencing is an efficient technique for generating huge sequences that can represent a large number of genes and their expression levels.ResultsWe used 454 sequencing for the de novo transcriptome assembly of persimmon fruit treated with 5% ethanol (Tr library) and without treatment as the control (Co library) to investigate the genes and pathways that control PA biosynthesis and other secondary metabolites. We obtained 374.6 Mb in clean nucleotides comprising 624,690 and 626,203 clean sequencing reads from the Tr and Co libraries, respectively. We also identified 83,898 unigenes; 54,719 (~65.2%) unigenes were annotated based on similarity searches with known proteins. Up to 14,954 of the unigenes were assigned to the protein database Clusters of Orthologous Groups (COG), 24,337 were assigned to the term annotation database of Gene Ontology (GO), and 45,506 were assigned to 200 pathways in the database of Kyoto Encyclopedia of Genes and Genomes (KEGG). The two libraries were compared to identify the differentially expressed unigenes. The expression levels of genes involved in PA biosynthesis and tannin coagulation were analysed, and some of them were verified using quantitative real time PCR (qRT-PCR).ConclusionsThis study provides abundant genomic data for persimmon and offers comprehensive sequence resources for persimmon research. The transcriptome dataset will improve our understanding of the molecular mechanisms of tannin coagulation and other biochemical processes in persimmons.
Highlights
The persimmon Diospyros kaki Thunb. is an important commercial and deciduous fruit tree
Persimmon cultivars are classified into four types, including pollination-constant nonastringent (PCNA), pollination-constant astringent (PCA), pollination-variant nonastringent (PVNA), and pollination-variant astringent (PVA); this classification is based on the effect of pollination on flesh colour and
Sequencing and assembly The soluble PA concentration of the Chinese PCNA (CPCNA) persimmon fruit was
Summary
The persimmon Diospyros kaki Thunb. is an important commercial and deciduous fruit tree. PAs cause astringency that is often undesirable for human consumption; the removal of astringency is an important practice in the persimmon industry. Persimmon cultivars are classified into four types, including pollination-constant nonastringent (PCNA), pollination-constant astringent (PCA), pollination-variant nonastringent (PVNA), and pollination-variant astringent (PVA); this classification is based on the effect of pollination on flesh colour and to be an important parent in PCNA persimmon breeding in the future. ‘Luotian-tianshi’ (D. kaki Thunb.; 2n = 6X = 90) is the first PCNA persimmon native to China, and it is only distributed in Dabieshan Mountain around the junction of Hubei, Henan, and Anhui provinces in central China [4,8]. Most persimmon fruits accumulate proanthocyanidins (PAs) in their flesh during development, causing the sensation of astringency due to the coagulation of oral proteins [9]. The primary genes involved in PA biosynthesis have not yet been determined
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