Transcriptome Analysis of Drought Induced Stress in <i>Chenopodium quinoa</i>

Quinoa (Chenopodium quinoa Willd.) is a halophytic, allotetraploid grain crop of the Amaranthaceae family with impressive drought tolerance, nutritional content and an increasing worldwide market. Here we report the results of an RNA-seq transcriptome analysis of Chenopodium quinoa using four water treatments (field capacity to drought) on the varieties “Ingapirca” (representing valley ecotypes) and “Ollague” (representing Altiplano Salares ecotypes). Physiological results, including growth rate, photosynthetic rate, stomatal conductance, and stem water potential, support the earlier findings that the Altiplano Salares ecotypes display greater tolerance to drought-like stress conditions than the valley ecotypes. cDNA libraries from root tissue samples for each variety × treatment combination were sequenced using Illumina Hi-Seq technology in an RNA-seq experiment. De novo assembly of the transcriptome generated 20,337 unique transcripts. Gene expression analysis of the RNA-seq data identified 462 putative gene products that showed differential expression based on treatment, and 27 putative gene products differentially expressed based on variety × treatment, including significant expression differences in root tissue in response to increasing water stress. BLAST searches and gene ontology analysis show an overlap between drought tolerance stress and other abiotic stress mechanisms.

Transcriptome profile of Dunaliella salina in Yuncheng Salt Lake reveals salt-stress-related genes under diff erent salinity stresses

Salt stress is an abiotic stress to plants in especially saline lakes.Dunaliella,a halophilic microalga distributed throughout salt lakes and seas,can respond to different salinity stresses by regulating the expression of some genes.However,these genes and their function and biological processes involved remain unclear.Profi ling these salt-stress-related genes in a high-salt-tolerant Dunaliella species will help clarify the salt tolerance machinery of Dunaliella.Three D.salina_YC salt-stress groups were tested under low(0.51 mol/L),moderate(1.03 mol/L),and high(3.42 mol/L)NaCl concentrations and one control group under very low(0.05 mol/L)NaCl concentration and 3 transcriptome results that were deep sequenced and de novo assembled were obtained per group.Twelve high-quality RNA-seq libraries with 46585 upregulated and 47805 downregulated unigenes were found.Relative to the control,188 common differentially expressed genes(DEGs)were screened and divided into four clusters in expression pattern.Fifteen of them annotated in the significant enriched Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)were validated via qPCR.Their qPCR-based relative expression patterns were similar to their RNA-seq-based patterns.Two significant DEGs,the geranylgeranyl diphosphate synthase coding gene(1876-bp cDNA)and diacylglycerol O-acyltransferase coding gene(2968-bp cDNA),were cloned and analyzed in silico.The total lipid content,superoxide dismutase specific activity,and betacarotene content of D.salina_YC increased gradually with increasing salinity.In addition,the expression of 11 validated genes involved in fatty acid biosynthesis/degradation,active oxygen or carotenoid metabolisms showed significant changes.In addition,algal photochemical efficiency was diminished with increasing salinity,as well as the expression of 4 photosynthesis-related genes.These results could help clarify the molecular mechanisms underlying D.salina responses to the Yuncheng Salt Lake environment and lay a foundation for further utilization of this algal resource.

Transcriptome analysis to identify candidate genes related to chlorogenic acid biosynthesis during development of Korla fragrant pear in Xinjiang

Korla fragrant pear(KFP)with special fragrance is a unique cultivar in Xinjiang,China.In order to explore the biosynthesis molecular mechanism of chlorogenic acid(CGA)in KFP,the samples at different development periods were collected for transcriptome analysis.High performance liquid chromatography analysis showed that CGA contents of KFP at 88,118 and 163 days after full bloom were(20.96±1.84),(12.01±0.91)and(7.16±0.41)mg/100 g,respectively,and decreased with the fruit development.Pears from these typical 3 periods were selected for de novo transcriptome assemble and 68059 unigenes were assembled from 444037960 clean reads.One‘phenylpropanoid biosynthesis’pathway including 57 unigenes,11 PALs,1 PTAL,64CLs,9 C4Hs,25 HCTs and 5 C3’Hs related to CGA biosynthesis was determined.It was found that the expression levels of 11 differentially expressed genes including 1 PAL,2 C4Hs,34CLs and 5 HCTs were consistent with the change of CGA content.Quantitative polymerase chain reaction analysis further showed that 8 unigenes involved in CGA biosynthesis were consistent with the RNA-seq data.These findings will provide a comprehensive understanding and valuable information on the genetic engineering and molecular breeding in KFP.

Genome assembly of KA105,a new resource for maize molecular breeding and genomic research

Superior inbred lines are central to maize breeding as sources of natural variation.Although many elite lines have been sequenced,less sequencing attention has been paid to newly developed lines.We constructed a genome assembly of the elite inbred line KA105,which has recently been developed by an arti-ficial breeding population named Shaan A and has shown desirable characteristics for breeding.Its pedigree showed genetic divergence from B73 and other lines in its pedigree.Comparison with the B73 reference genome revealed extensive structural variation,58 presence/absence variation(PAV)genes,and 1023 expanded gene families,some of which may be associated with disease resistance.A network-based integrative analysis of stress-induced transcriptomes identified 13 KA105-specific PAV genes,of which eight were induced by at least one kind of stress,participating in gene modules responding to stress such as drought and southern leaf blight disease.More than 200,000 gene pairs were differentially correlated between KA105 and B73 during kernel development.The KA105 reference genome and transcriptome atlas are a resource for further germplasm improvement and surveys of maize genomic variation and gene function.

Transcriptome Analysis of Reaction Wood in Gymnosperms by Next-Generation Sequencing

Special xylem tissue called “compression wood” is formed on the lower side of inclined stems when gymnosperms grow on a slope. We investigated the molecular mechanism of compression wood formation. Transcriptome analysis by next-generation sequencing (NGS) was applied to the xylem of Chamaecyparis obtusa to develop a catalog of general gene expression in differentiating xylem during compression and normal wood formation. The sequencing output generated 234,924,605 reads and 40,602 contigs (mean size = 529 bp). Based on a sequence similarity search with known proteins, 54.2% (22,005) of the contigs showed homology with sequences in the databases. Of these annotated contigs, 19,293 contigs were assigned to Gene Ontology categories. Differential gene expression between the compression and normal wood libraries was analyzed by mapping the reads from each library to the assembled contigs. In total, 2875 contigs were identified as differentially expressed, including 1207 that were up-regulated and 1668 that were down-regulated in compression wood. We selected 30 genes and compared the transcript abundance between compression and normal wood by quantitative polymerase chain reaction analysis to validate the NGS results. We found that 27 of the 30 genes showed the same expression patterns as the original NGS results.

De novo assembly and comparative analysis of root transcriptomes from different varieties of Panax ginseng C. A. Meyer grown in different environments

Panax ginseng C. A. Meyer is an important traditional herb in eastern Asia. It contains ginsenosides, which are primary bioactive compounds with medicinal properties. Although ginseng has been cultivated since at least the Ming dynasty to increase production, cultivated ginseng has lower quantities of ginsenosides and lower disease resistance than ginseng grown under natural conditions. We extracted root RNA from six varieties of fifth-year P. ginseng cultivars representing four different growth conditions, and performed Illumina paired-end sequencing. In total, 163,165,706 raw reads were obtained and used to generate a de novo transcriptome that consisted of 151,763 contigs(76,336 unigenes), of which 100,648 contigs(66.3%) were successfully annotated. Differential expression analysis revealed that most differentially expressed genes(DEGs) were upregulated(246 out of 258, 95.3%) in ginseng grown under natural conditions compared with that grown under artificial conditions. These DEGs were enriched in gene ontology(GO) terms including response to stimuli and localization. In particular, some key ginsenoside biosynthesis-related genes, including HMG-Co A synthase(HMGS), mevalonate kinase(MVK), and squalene epoxidase(SE), were upregulated in wild-grown ginseng. Moreover, a high proportion of disease resistance-related genes were upregulated in wild-grown ginseng. This study is the first transcriptome analysis to compare wild-grown and cultivated ginseng, and identifies genes that may produce higher ginsenoside content and better disease resistance in the wild; these genes may have the potential to improve cultivated ginseng grown in artificial environments.

Chromosome Scale Genome Assembly andTranscriptome Profiling of Nannochloropsisgaditana in Nitrogen Depletion

Nannochloropsis is rapidly emerging as a model organism for the study of biofuel production in microalgae.Here, we report a high-quality genomic assembly of Nannochloropsis gaditana, consisting of large contigs, up to 500 kbplong, and scaffolds that in most cases span the entire length of the chromosomes. We identified 10646 complete genesand characterized possible alternative transcripts. The annotation of the predicted genes and the analysis of cellular pro-cesses revealed traits relevant for the genetic improvement of this organism such as genes involved in DNA recombina-tion, RNA silencing, and cell wall synthesis. We also analyzed the modification of the transcriptional profile in nitrogendeficiencyma condition known to stimulate lipid accumulation. While the content of lipids increased, we did not detectmajor changes in expression of the genes involved in their biosynthesis. At the same time, we observed a very signifi-cant down-regulation of mitochondrial gene expression, suggesting that part of the AcetyI-CoA and NAD（P）H, normallyoxidized through the mitochondrial respiration, would be made available for fatty acids synthesis, increasing the fluxthrough the lipid biosynthetic pathway. Finally, we released an information resource of the genomic data of IV. gaditana,available online at www.nannochloropsis.org.

De novo transcriptome assembly of RNA-Seq reads with different strategies

De novo transcriptome assembly is an important approach in RNA-Seq data analysis and it can help us to reconstruct the transcriptome and investigate gene expression profiles without reference genome sequences.We carried out transcriptome assemblies with two RNA-Seq datasets generated from human brain and cell line,respectively.We then determined an efficient way to yield an optimal overall assembly using three different strategies.We first assembled brain and cell line transcriptome using a single k-mer length.Next we tested a range of values of k-mer length and coverage cutoff in assembling.Lastly,we combined the assembled contigs from a range of k values to generate a final assembly.By comparing these assembly results,we found that using only one k-mer value for assembly is not enough to generate good assembly results,but combining the contigs from different k-mer values could yield longer contigs and greatly improve the overall assembly.

Comparative analysis of de novo transcriptome assembly

The fast development of next-generation sequencing technology presents a major computational challenge for data processing and analysis.A fast algorithm,de Bruijn graph has been successfully used for genome DNA de novo assembly;nevertheless,its performance for transcriptome assembly is unclear.In this study,we used both simulated and real RNA-Seq data,from either artificial RNA templates or human transcripts,to evaluate five de novo assemblers,ABySS,Mira,Trinity,Velvet and Oases.Of these assemblers,ABySS,Trinity,Velvet and Oases are all based on de Bruijn graph,and Mira uses an overlap graph algorithm.Various numbers of RNA short reads were selected from the External RNA Control Consortium(ERCC) data and human chromosome 22.A number of statistics were then calculated for the resulting contigs from each assembler.Each experiment was repeated multiple times to obtain the mean statistics and standard error estimate.Trinity had relative good performance for both ERCC and human data,but it may not consistently generate full length transcripts.ABySS was the fastest method but its assembly quality was low.Mira gave a good rate for mapping its contigs onto human chromosome 22,but its computational speed is not satisfactory.Our results suggest that transcript assembly remains a challenge problem for bioinformatics society.Therefore,a novel assembler is in need for assembling transcriptome data generated by next generation sequencing technique.

Comparative study of de novo assembly and genome-guided assembly strategies for transcriptome reconstruction based on RNA-Seq

Transcriptome reconstruction is an important application of RNA-Seq,providing critical information for further analysis of transcriptome.Although RNA-Seq offers the potential to identify the whole picture of transcriptome,it still presents special challenges.To handle these difficulties and reconstruct transcriptome as completely as possible,current computational approaches mainly employ two strategies:de novo assembly and genome-guided assembly.In order to find the similarities and differences between them,we firstly chose five representative assemblers belonging to the two classes respectively,and then investigated and compared their algorithm features in theory and real performances in practice.We found that all the methods can be reduced to graph reduction problems,yet they have different conceptual and practical implementations,thus each assembly method has its specific advantages and disadvantages,performing worse than others in certain aspects while outperforming others in anther aspects at the same time.Finally we merged assemblies of the five assemblers and obtained a much better assembly.Additionally we evaluated an assembler using genome-guided de novo assembly approach,and achieved good performance.Based on these results,we suggest that to obtain a comprehensive set of recovered transcripts,it is better to use a combination of de novo assembly and genome-guided assembly.

Genome assembly and transcriptome analysis provide insights into the antischistosome mechanism of Microtus fortis

Microtus fortis is the only mammalian host that exhibits intrinsic resistance against Schistosoma japonicum infection.However,the underlying molecular mechanisms of this resistance are not yet known.Here,we perform the first de novo genome assembly of M.fortis,comprehensive gene annotation analysis,and evolution analysis.Furthermore,we compare the recovery rate of schistosomes,pathological changes,and liver transcriptomes between M.fortis and mice at different time points after infection.We observe that the time and type of immune response in M.fortis are different from those in mice.M.fortis activates immune and inflammatory responses on the 10th day post infection,such as leukocyte extravasation,antibody activation,Fc-gamma receptor-mediated phagocytosis,and the interferon signaling cascade,which play important roles in preventing the development of schistosomes.In contrast,an intense immune response occurrs in mice at the late stages of infection and could not eliminate schistosomes.Infected mice suffer severe pathological injury and continuous decreases in cell cycle,lipid metabolism,and other functions.Our findings offer new insights into the intrinsic resistance mechanism of M.fortis against schistosome infection.The genome sequence also provides the basis for future studies of other important traits in M.fortis.

A Comprehensive Transcriptome Assembly of Pigeonpea （Cajanus cajan L.） using Sanger and Second-Generation Sequencing Platforms

A comprehensive transcriptome assembly for pigeonpea has been developed by analyzing 128.9 million short Illumina GA IIx single end reads, 2.19 million single end FLX/454 reads, and 18 353 Sanger expressed sequenced tags from more than 16 genotypes. The resultant transcriptome assembly, referred to as CcTA v2, comprised 21 434 transcript as- sembly contigs （TACs） with an N50 of 1510 bp, the largest one being -8 kb. Of the 21 434 TACs, 16 622 （77.5%） could be mapped on to the soybean genome build 1.0.9 under fairly stringent alignment parameters. Based on knowledge of intron junctions, 10 009 primer pairs were designed from 5033 TACs for amplifying intron spanning regions （ISRs）. By using in silico mapping of BAC-end-derived SSR loci of pigeonpea on the soybean genome as a reference, putative mapping posi- tions at the chromosome level were predicted for 6284 ISR markers, covering all 11 pigeonpea chromosomes. A subset of 128 ISR markers were analyzed on a set of eight genotypes. While 116 markers were validated, 70 markers showed one to three alleles, with an average of 0.16 polymorphism information content （PIC） value. In summary, the CcTA v2 transcript assembly and ISR markers will serve as a useful resource to accelerate genetic research and breeding applications in pigeonpea.

De novo assembly of transcriptome from next-generation sequencing data

Reconstruction of transcriptome by de novo assembly from next generation sequencing （NGS） short-sequence reads provides an essential mean to catalog expressed genes, identify splicing isoforms, and capture the expression detail of transcripts for organisms with no reference genome available. De novo transcriptome assembly faces many unique challenges, including alternative splicing, variable expression level covering a dynamic range of several orders of magnitude, artifacts introduced by reverse transcription, etc. In the current review, we illustrate the grand strategy in applying De Bruijn Graph （DBG） approach in de novo transcriptome assembly. We further analyze many parameters proven critical in transcriptome assembly using DBG. Among them, k-met length, coverage depth of reads, genome complexity, performance of different programs are addressed in greater details. A multi-k-mer strategy balancing efficiency and sensitivity is discussed and highly recommended for de novo transcriptome assembly. Future direction points to the combination of NGS and third generation sequencing technology that would greatly enhance the power of de novo transcriptomics study.

高通量转录组测序技术及其在鳞翅目昆虫上的应用

转录组是指组织或者细胞在某一特定状态下转录出来的所有RNA的集合。高通量第2代测序技术使转录组学的研究模式发生了巨大的改变,所衍生出的转录组测序迅速成为研究非模式生物的先进技术。转录组测序能够在整体水平上探究细胞内基因表达的种类和数量,揭示在特定条件下机体生理生化发生过程以及其中的分子机理。本文简要阐述了转录组测序技术的基本概念、技术流程与原理,详细介绍了转录组测序在解决鳞翅目昆虫的分类、毒理、发育、与寄主互作以及非编码RNA调控等问题上做出的贡献,并对该技术现存的困难进行了系统的阐述并对其未来的发展趋势作出了简要的预测与剖析。

基于Illumina高通量测序的泡桐转录组研究

利用新一代高通量测序技术平台Illumina Solexa对泡桐进行转录组测序和数据denovo组装,并对得到的unigene进行功能注释、分类及代谢通路分析。结果表明,N50值为2278bp、平均长度为1410bp的泡桐unigene共有188019条,将其与NCBI的Nr和Swiss-Prot数据库比对后发现,分别有120808条和85880条unigene与其他物种的基因具有同源性。利用COG数据库可将有关的41914条泡桐unigene分成25类,KEGG数据库分析发现共有43553个unigene参与215种代谢通路。找到与木质素合成相关的泡桐unigene。

化学诱导后白木香转录组文库的构建与测序

采用改良异硫氰酸胍-CTAB法对5年生白木香树干经化学诱导后1年的各部分组织进行总RNA提取,提取到的总RNA经富集mRNA、打断、构建测序用cDNA文库后用于转录组测序,测序质量较高,Q20高达97.45%,共获得54 685 634条Clean reads,总测序长度达4 921 707 060 nt,经初步组装,获得190 109条Contigs序列,进一步组装,获得83 467条Unigenes序列,总长度为58 569 625 nt,平均长度为702 nt,N50值高达1 120,大于等于3 000 nt的Unigenes有1 691条,占总Unigenes的2.03%,组装质量较高,使白木香的转录组信息得到较好的保存,为进行白木香结香相关的表达谱分析奠定基础。

杉木转录组SSR挖掘及EST-SSR标记规模化开发

【目的】为解决杉木SSR标记数量不足、已开发的位点多态性较差等问题,以杉木转录组测序数据为基础,结合多重PCR技术批量挖掘SSR,规模化开发EST-SSR位点,为杉木分子遗传学研究奠定良好基础。【方法】杉木转录组序列数据（Accession：SRX151872）从NCBI的SRA数据库下载。利用CLC和CMi B软件批量挖掘SSR位点;利用四色荧光标记通用引物多重PCR（multiplex-PCR）技术实现SSR标记的规模化开发。【结果】杉木转录组de novo assembly序列拼接共得到35 633个contigs,总长度31.5 Mb,其中最小拼接长度155 bp,最大23 794 bp,平均长度884 bp。得到2 156个SSR位点,分布于1 822个contigs中,其中256个contigs中包含1个以上SSR位点,复合型SSR数量为118个,SSR平均分布密度为68.4个/Mb。不同SSR重复单元（motif）中,三核苷酸SSR重复单元数量最多,占总数的41.7%。批量引物设计得到1 582个有效位点的引物对,占SSR位点总数的73.4%。利用四色荧光标记通用引物多重PCR检测技术,对35个候选标记位点进行多态性检测,其中28个位点具有多态性,多态性位点比例达到80%,检测位点多态信息含量（PIC）平均值为0.573,表明所开发的EST-SSR位点具有很高的多态性。PCA分析结果表明,28个EST-SSR多态性位点具有很强的鉴别杉木不同地理种源,甚至同一种源不同单株的能力。【结论】将转录组SSRs挖掘和四色荧光标记通用引物多重PCR技术相结合,成功建立杉木EST-SSR高效开发流程和方法,得到较多高质量的EST-SSR标记位点,这些位点已用于后续杉木遗传多样性保护研究。与传统SSR标记位点开发技术相比较,转录组海量序列为高质量多态性位点的选择可提供充足的数据保证。四色荧光标记通用引物基因分型结果清晰、稳定可靠,不但试验成本仅为原来的10%-15%,而且结合多重PCR扩增技术,可使试验效率提高5-6倍。新方法的建立和应用不仅能促进杉木分子遗传学相关研究,而且对其他非模式生物或新物种SSR标记开发也具有重要的参考作用。

基于RNA-seq技术对乌鳢和斑鳢肝脏的转录组分析

为满足标记辅助育种的要求,通过Illumina Solexa测序平台首次开展了乌鳢和斑鳢肝脏转录组测序。结果表明:乌鳢和斑鳢样本中分别得到85 802个和52 769个转录本,大小分别为113.75 Mb和44.29 Mb,组装后分别得到59 959个和44 337个Unigene,大小分别为45 Mb和27 Mb,序列平均长度为751.99 bp和608.88 bp。基因功能注释研究共获取了26 284个和24 812个特异蛋白,根据特异蛋白注释结果进行GO分析,分别有20 682和21 752条Unigene有GO注释;采用GO功能分类工具可将已注释转录物序列划分为分子功能、生物途径和细胞成分3类,为下一步开展生长等性状相关基因功能验证研究以及分子标记辅助育种等提供了丰富的序列资源。

基于RNA-Seq技术的鲮转录组分析

为满足标记辅助育种的要求,通过454测序平台首次开展了鲮Cirrhina molitorella全鱼转录组深度测序,并用Newbler等软件进行数据精细分析。结果表明:共获得了1 297 479条reads,总碱基数为486 586 191 bp,组装后得到19 962条contigs,平均长度为1269 bp,N50为1509 bp。基因功能注释研究共获取了10 577个特异蛋白,根据特异蛋白注释结果进行GO分析,有7314条contigs有GO注释,包含5381个特异蛋白;采用GO功能分类工具可将已注释转录物序列划分为分子功能、生物途径和细胞成分3类,为下一步开展生长等性状相关基因功能验证研究提供丰富的序列资源;共鉴定出5931个具有完整的ORF的全长c DNA序列,并且鉴定出2438个微卫星和5014个SNP位点。本研究中,还建立了鲮转录组数据库和网站,方便同行随时调取数据,这为深入开展鲮分子标记辅助的遗传育种、种群遗传学和资源评估等研究提供了丰富的标记资源。

青霉菌侵染前后哈密瓜转录组的构建及分析

丰富的营养物质容易被青霉菌侵染,从而导致哈密瓜的腐坏变质。利用Illumina测序技术考察青霉病原菌侵染前后哈密瓜基因转录组水平的差异变化。利用Illumina平台测序并分析了哈密瓜的转录组信息。过滤后的Clean Reads包含4 947 555 420 nt的碱基数,对Clean Reads进行组装,获得了50 502条Unigene。在NR数据库中,以E value值10-5为截点进行BLAST比对,共有71.28%的Unigenes比对到该数据库中。但还有10 526条Unigene没有比对到NR、NT和Swiss-Prot数据库,可能是哈密瓜果实区别于其它物种而特有的基因,这需要进一步验证。将本次转录组测序得到的39 976个Unigene比对到KEGG数据库进行Pathway注释,共映射到不同的代谢通路128个。