Comparative Transcriptomic Analysis Revealed Adaptation Mechanism To Environments Of Two Phrynocephalus Lizards In The Tarim Basin

The Tarim Basin is bounded by the Tianshan Mountains to the north,the Pamir Plateau to the west,the Kunlun Mountains to the south,and the Taklamakan Desert to the center.As a result of global warming,the temperature in the basin tends to increase year by year,while the mountainous areas around the basin show low temperature and hypoxia as well as strong UV radiation.Therefore,the Tarim Basin provides an opportunity to study the adaptation of animals to two different environments: high temperature and low temperature and hypoxia.Phrynocephalus forsythii and Phrynocephalus axillaris are closely related species of Phrynocephalus,and their distribution areas in the Tarim Basin overlap to a large extent,which,together with their physiological functions,are directly limited by environment temperature,making them ideal materials for studying the adaptation mechanisms of animals to different environments.In order to explore the adaptation mechanisms and similarities between P.forsythii and P.axillaris to high temperature and low temperature hypoxic environments,this study was conducted on two sympatric populations,Cele（low temperature hypoxic group）and Yuli（high temperature group）populations of two Phrynocephalus lizards.The transcriptome of P.forsythii was analyzed by reference genome,while transcriptome of P.axillaris was analyzed by de novo（sequence their heart,brain,lung,gonad and kidney tissues）by the Illumina Hiseq^TM 4000 platform.The GO terms,metabolic pathways,key genes related to environmental adaptation were screened by bioinformatics analysis,and the selected genes were verified by fluorescence real-time quantitative PCR.The functional aspects of the pathways and key genes were used to elucidate the adaptive mechanisms of the two species in response to high temperature and low temperature hypoxic environments.The main results are as follows:（1）Based on | log2（fold change）| > 1 and Padj <0.05,1605,1985,1820,915 and2194 significant differentially expressed genes were screened in the heart,brain,lung,gonad and kidney tissues of P.forsythii.738,1406,1013,723 and 2761 significant differentially expressed genes were screened in above tissues of P.axillaris,respectively.（2）The GO analysis showed that the differentially expressed genes in five tissues were mainly enriched in “energy derivation by oxidation of organic compounds”,“cellular respiration”,“ribose phosphate metabolic process”,“oxidoreductase activity,acting on NAD（P）H”,etc in the high temperature group of P.forsythii.The differentially expressed genes were mainly enriched in “ribosome”,“oxidative phosphorylation” and other biosynthesis related annotations in the high temperature group of P.axillaris.Under low temperature and hypoxia environment,the up-regulated differentially expressed genes were mainly enriched in “growth and development”,“serine-type endopeptidase activity”,“serine hydrolase activity”,“DNA replication” and terms related to metabolism-related processes,while“peptidase inhibitor activity”,“endopeptidase regulator activity” were the main enrichment terms in P.axillaris.These results suggest that the adaptation of two Phrynocephalus lizards to high temperature is mainly related to energy metabolism and cell activities,while the adaptation to low temperature and hypoxia may involve energy metabolism and the regulation of enzyme activities.（3）The KEGG analysis showed that the up-regulated genes in high temperature environment were involved in energy metabolism,hypoxia response,osmotic regulation and protein damage repair,and were mainly enriched in oxidative phosphorylation,proteasome,protein processing in endoplasmic reticulum and cardiac muscle contraction.HSP40,HSP70,HSP90,PDIA3,PDIA6,ACAD8,ACTC1 and other genes were involved.The up-regulated genes were involved in energy metabolism and immune response,and were mainly enriched in PPAR signaling pathway,AMPK signaling pathway,insulin resistance,glucagon signaling pathway and some disease immune-related pathways,involving ACACB,CPT1 A,FASN,CD36 and other genes.The results suggested that two species might adopt different adaptive mechanisms to cope with high temperature stress.Under low temperature and hypoxia environment,both P.forsythii and P.axillaris adapt to the environment from the aspects of energy metabolism,hypoxia response and DNA repair damage.The up-regulated genes in P.forsythii were mainly enriched in neuroactive ligand-receptor interaction,cytokine-cytokine receptor interaction,focal adhesion,ECM-receptor interaction,PPAR signaling pathway and cell adhesion molecules（CAMs）,involving VEGFA,FEN1,FABP1,PLK1,PIK3 CB and other genes.The up-regulated genes in P.axillaris were mainly enriched in circadian rhythm,hematopoietic cell lineage involving PER2,CRY,NR1D1,BHLHB3,TFRC,EPOR,etc.In conclusion,the adaptation of P.forsythii and P.axillaris to these two environments showed a certain degree of convergence.Firstly,the genes related to energy metabolism（ND1,ND6,CYTB,COX1,COX2,COX3,and ATP6）were significantly up-regulated in the lung tissues of two Phrynocephalus lizards,which may indicate the convergence of energy metabolism.Secondly,although the gene expressions of the two species were not identical,their functional responses to low temperature hypoxic environments were consistent,suggesting a convergent evolution of the two species during their adaptation to low temperature and hypoxic stress.This study revealed the adaptive mechanisms of the sympatric P.forsythii and P.axillaris to high temperature and low temperature hypoxic environment at the transcriptome level.Multiple metabolic pathways and key genes related to high temperature and low temperature hypoxic adaptation were found,which provided genomic and functional evidence for further understanding the adaptive mechanisms and convergent evolution of reptiles.