Abstract
BackgroundAmmopiptanthus mongolicus (Maxim. ex Kom.) Cheng f., an evergreen broadleaf legume shrub, is distributed in Mid-Asia where the temperature can be as low as −30°C during the winter. Although A. mongolicus is an ideal model to study the plant response to cold stress, insufficient genomic resources for this species are available in public databases. To identify genes involved in cold acclimation (a phenomenon experienced by plants after low temperature stress), a high-throughput sequencing technology was applied.ResultsWe sequenced cold-treated and control (untreated) samples of A. mongolicus, and obtained 65,075,656 and 67,287,120 high quality reads, respectively. After de novo assembly and quantitative assessment, 82795 all-unigenes were finally generated with an average length of 816 bp. We then obtained functional annotations by aligning all-unigenes with public protein databases including NR, SwissProt, KEGG and COG. Differentially expressed genes (DEGs) were investigated using the RPKM method. Overall, 9309 up-regulated genes and 23419 down-regulated genes were identified. To increase our understanding of these DEGs, we performed GO enrichment and metabolic pathway enrichment analyses. Based on these results, a series of candidate genes involved in cold responsive pathways were selected and discussed. Moreover, we analyzed transcription factors, and found 720 of them are differentially expressed. Finally, 20 of the candidate genes that were up-regulated and known to be associated with cold stress were examined using qRT-PCR.ConclusionsIn this study, we identified a large set of cDNA unigenes from A. mongolicus. This is the first transcriptome sequencing of this non-model species under cold-acclimation using Illumina/Solexa, a next-generation sequencing technology. We sequenced cold-treated and control (untreated) samples of A. mongolicus and obtained large numbers of unigenes annotated to public databases. Studies of differentially expressed genes involved in cold-related metabolic pathways and transcription factors facilitate the discovery of cold-resistance genes.
Highlights
Ammopiptanthus mongolicus (Maxim. ex Kom.) Cheng f., an evergreen broadleaf legume shrub, is distributed in Mid-Asia where the temperature can be as low as −30°C during the winter
Genome-size estimates We determined the genome size of A. mongolicus by flow cytometry using cotyledons nuclei with maize (≈2500 Mb [27]) as an internal standard
The result showed that the genome size of A. mongolicus (2n = 18) was approximately 819.56 ± 7.61 Mb (Table 1), which was similar to that of another legume, the chick pea (Cicer arietinuum, ≈738 Mb) [28]
Summary
Ammopiptanthus mongolicus (Maxim. ex Kom.) Cheng f., an evergreen broadleaf legume shrub, is distributed in Mid-Asia where the temperature can be as low as −30°C during the winter. Ex Kom.) Cheng f., an evergreen broadleaf legume shrub, is distributed in Mid-Asia where the temperature can be as low as −30°C during the winter. Cold acclimation; i.e., enhancement of the freezing tolerance of plants after low temperature stress, has been observed in many plants, including Arabidopsis [12], Oryza sativa [13], Triticum aestivum [14], and A. mongolicus [15]. During this process, plants alter the expression of certain genes as well as the biosynthesis of amino acids and soluble sugars. To elucidate the mechanism underlying cold acclimation, it is important to determine how plants alter gene expression in response to this biological process [16]
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