Comparative Transcriptome Analysis Reveal Adaptive Differentiation Of Opisthopappus

Species differentiation is the basis and premise of biodiversity,and is the core issue and research hotspot of evolutionary biology.Opisthopappus is an endemic genus of the Taihang Mountains that includes only two spatially partitioned species,Opisthopappus longilobus and Opisthopappus taihangensis.The unique ecological environment of Taihang Mountains,with variable localized climate and topographic complexity,makes it an ideal area for studying the adaptive evolution of species under a local scale.In this study,through the comparative transcriptome analysis and environmental effects analysis of Opisthopappus,we have identified the differentially expressed genes,the single-copy orthologous genes under positive selection and the key climatic factors which may play important roles in the adaptive differentiation of Opisthopappus.The results showed that there were 5.35E+05 and 2.64E+05Unigenes in the transcriptome of O.longilobus and O.taihangensis,respectively.The Unigenes were annotated in NR(O.longilobus: 37.48%;O.taihangensis: 35.91%),GO(O.longilobus: 18.65%;O.taihangensis: 12.25%),KEGG(O.longilobus: 1.22%;O.taihangensis: 2.38%),egg NOG(O.longilobus: 34.24%;O.taihangensis: 37.66%)and Swiss-Prot(O.longilobus: 46.36%;O.taihangensis: 48.47%)databases.Among 3410 differentially expressed genes identified in Opisthopappus,1925 genes were up-regulated and1485 genes were down-regulated(O.longilobus vs O.taihangensis).The differentially expressed genes were significantly enriched in metabolism,energy transfer,signal transduction,environmental adaptation and other GO term or KEGG pathway.59753 pairs of single-copy orthologous genes were identified and in which 5832 pairs of them were under positive selection.These genes were significantly enriched in biological pathways such as transcriptional regulation,binding to cell substances or components,photosynthesis,polysaccharide synthesis and so on.Among the top ten differentially expressed genes,Unigene c286931＿g1＿i1,up-regulated in O.taihangensis and down-regulated in O.longilobus,was significantly enriched in four GO terms(photosynthesis,carbohydrate metabolism,endogenous stimulation response and chemical response)and two KEGG pathways(carbohydrate metabolism and pentose phosphate pathway).Orthologous genes GR37042(O.longilobus:TRINITY＿DN135624＿c0＿g1),under the positive selection,and was significantly enriched in six GO terms(DNA binding,transcriptional activity regulation,DNA binding transcriptional activity regulation,nuclear and nucleic acid complex metabolism process)and one KEGG pathway(transcription factor).According to the annotation results,the former was fructose-1,6-diphosphate and the latter was CCAAT box binding factor.It was speculated that these two genes might play essential roles in the adaptive evolution of Opisthopappus,and they were regarded as candidate genes.The results of environmental effects analysis showed that the local environmental heterogeneity affected the genetic differentiation of Opisthopappus.The results of Mantel test,MMRR and db RDA consistently showed that the genetic distances were significantly related to the geographical and environmental distances,and environmental variables could explain more than 60% of the genetic differentiation.The results of forward selection of explanatory variables showed that the bio6(Min Temperature of Coldest Month)and bio14(Precipitation of Driest Month)could be regarded as the key climatic factors in governing the genetic differentiation and genetic structure of Opisthopappus.