Phylogeography And Transcriptome In Response To Waterlogging Studies Of Pterocarya Stenoptera

Pterocarya stenoptera C.DC(Juglandaceae)grows in the forests along the riverbanks and wet hillsides along the rivers below 1500 meters above sea level.In this study,we selected Pterocarya stenoptera,which is widespread species in China,to investigate its phylogeographical pattern and the differences in transcriptome expression under water flooding stress.Based on Illumina sequencing of the transcriptome of Pterocarya stenoptera,a total of 2452 microsatellites were identified from 83,674 assembled unigenes.One hundred microsatellites were randomly selected to design amplification primer pairs.Of these,15 were successfully amplified and displayed polymorphism.Four noncoding spacers,eight microsatellite(simple sequence repeat)markers,and species distribution modeling were used to examine the phylogeographical pattern of Pterocarya stenoptera.Based on chloroplast DNA data,populations of Pterocaya stenoptera were clearly clustered into three groups.The divergence time of these groups fell into the stage of the Qinghai-Tibet Movement,1.7-2.6 Ma.For simple sequence repeat data,only one western marginal population YNYB could be separated from other populations,whereas other populations were mixed together.Our results indicated that the environmental heterogeneity resulting from the Qinghai-Tibet movement might be response for this genetic divergence.The climatic fluctuations in the Pleistocene did not cause the substantial range shift of Pterocarya stenoptera,while the fluctuations affected its population size.Moreover,we also confirmed the river systems did not act as channels or barrier of dispersal for Pterocarya stenoptera.The natural distribution of Pterocarya stenoptera is mainly near the stream.This study further reveals the molecular mechanism of Pterocarya stenoptera adaptation to waterlogging stress.We compared the changes in transcript levels and differentially expressed genes of Pterocarya stenoptera under different waterlogging time using RNA-seq technique in this experiment.The results showed that compared with the control,663 differentially expressed genes(DEGs)were identified at 3h,of which 350 DEGs were up-regulated and 313 DEGs were down-regulated;2704 DEGs were identified at 12h,of which 1247 DEGs were up-regulated and 1457 DEGs were down-regulated.GO enrichment showed that these DEGs are mainly concentrated in processes such as signal transduction,material metabolism and photosynthesis.KEGG pathway enrichment analysis showed that waterlogging stress repressed many genes that encode photosynthetic reactions,including light reactions and carbon-fixing reactions.In contrast,most genes that function in ROS-scavenging and degrading lipids were up-regulated.These results will contribute to elucidate the metabolic and molecular mechanisms of plants under short-term waterlogging stress.