| Oil-tea camellia(Camellia oleifera)is the top-one woody oil crop in China. Currently, the mean production per mu is very low in oil-tea camellia. At the same time, constraints such as lack of good cultivated varieties, limit the development of oil-tea camellia industry. Wild oil-tea camellia is the most important genetic resource for oil-tea camellia breeding. Developing a large amount of molecular markers suitable for analyzing genetic diversity in wild oil-tea camellia, and understanding the genetic structure of wild oil-tea camellia along latitude and altitude gradients, can facilitate the researches on wild oil-tea camellia genetic resource, and assist the breeding of cultivated oil-tea camellia, and therefore greatly improve the efficiency of oil-tea camellia breeding.In this study, wild oil-tea camellia leaf samples were collected from different altitudes in Lu and Jinggang mountains. The leaf transcriptomes were sequenced by the Illumina Hiseq 2000 platform. The resulted sequencing data were analyzed using bioinformatics methods to identify polymorphic loci. Samples from different altitudes in Lu and Jinggang mountains represented different air temperatures. By comparing the patterns of differentially expressed genes under different air temperatures, the key functional genes for cold tolerance in oil-tea camellia could be discovered.The main results and conclusions of this study are as follows:1) Our study obtained approximately 57.3 G high-quality transcriptome data of wild oil-tea camellia leaves. These sequences were assembled into more than 177 thousand unigenes, and the total length of the unigenes was more than 91 M. Among these unigenes, 85 thousands were functional annotated. It?s the largest reported transcriptome dataset which can provide huge amount of reference sequences for researches on functional genomics in the genus of Camellia.2) More than 660 thousand loci of single nucleotide polymorphisms(SNPs) were identified in our study, among which the number of synonymous SNPs is about 2 times of nonsynonymous SNPs. More than 47 thousand loci of insertion/deletion(Indel) were detected. In addition, more than 25 thousand loci of microsatellites(simple sequence repeats, SSRs) were discovered, and the main SSR types are mono-nucleotide repeat, di-nucleotide repeat, and tri-nucleotide repeat. The polymorphic loci identified in this study can be used to develop molecular markers in oil-tea camellia and other Camellia species, helping to analyze the genetic structure of wild oil-tea camellia from different latitudes and altitudes.3) Our study found that, the gene expression patterns of wild oil-tea camellia leaves were considerably different among different altitudes from Lu and Jinggang mountains, mainly owing to the differences in air temperatures. Being compared to the gene expression patterns under air temperatures of 10?C, 14?C and 18?C, the expression patterns under 2?C and 5?C were significantly different, with a large number of genes was up-regulated, which may be associated with the processes of cold tolerance in oil-tea camellia. In addition, differentially expressed genes under 2?C and 5?C were different, with more genes differentially expressed under 2?C. These results indicated that the expression of a large amount of genes related to cold tolerance increased with the decrease of air temperature.4) Among the 116 differentially expressed genes under 2?C and 5?C, 96 were functional annotated, including 69 genes with functions related to cold tolerance in plants. The candidate genes for cold tolerance were involved in sugar transmembrane transport, calcium ion transport, fatty acid metabolism, CBF(C-repeat binding factor), oxidation-reduction process, photosynthesis, ethylene responsive transcription factor, abscisic acid(ABA) etc. Our study provides the bases for understanding the molecular mechanisms of cold tolerance in oil-tea camellia and other evergreen broadleaf plants in the genus of Camellia. |
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