The Adaptive Evolution Between Two Ecotypes Of Lotus(Nelumbo Nucifera) By Transcriptome Sequencing

Lotus(Nelumbonaceae:Nelumbo),is a typical representative of relict plant,and it has the great reference value to study the origin and evolution of species.The Nelumbo contains two species: N.nucifera Gaertn.and N.lutea Pers.Due to the wide geographical distribution and large spans,many significant differences in morphological phenotype and growth habit are observed in two ecotypes: Temperate lotus and Tropical lotus.Temperate lotus is mainly distributed in the temperate zone even in the boreal zone,and It has obvious annual growth and development cycle with short flowering period and the underground stems swelling into large nutritious rhizome to against the cold weather.Tropical lotus is mainly located in tropic,and it grows without significant pauses and inflated rhizome throughout the year.In order to explore the difference of adaptive evolution between two ecotypes of lotus from the expression level,we collected samples of five temperate wild lotus and four tropical wild lotus respectively,and multi-level difference analysis between two ecotypes was executed based on transcriptome sequencing technique.The main results are as follows:(1)Base on transcriptome sequencing results of two ecotypes root and leaf tissue,the phylogenetic analysis of SNPs in 18 samples showed that there were obvious differences between the temperate lotus and tropical lotus,and the result proved that there was evolutionary separation in the two ecotypes.(2)Gene expression clustering analysis of each sample showed that most genes had differences in expression between root and leave tissues,proving that the gene expression patterns of root and leaf were different.No obvious clustering phenomenon in the gene expression was obseved between the two ecotypes,indicating that the overall level of gene expression had no obvious difference between two ecotypes in the early growth stage of lotus.However,this result can not rule out that a small number of genes have been differentiated in expression between two ecotypes.(3)81 and 51 differentially expressed genes(DEGs)were obtained from 9 leaf and root samples respectively,and there were 23 DEGs were shared in two tissues.Among all the DEGs,9 genes were highly expressed in the temperate lotus and almost none expressed in the tropical lotus,inversely 8 genes were highly expressed in the tropical lotus and hardly expressed in the temperate lotus.These 17 specifically expressed genes are likely involved in the adaptive evolution of two ecotypes of lotus.(4)Based on the GO,COG classification and KEGG pathway enrichment analysis of DEGs in two ecotypes,it was found that the expression quantity of genes which involved in glycolysis,gluconeogenesis,starch and sucrose metabolism were more higher in temperate lotus than in tropical lotus.And it was speculated that the phenomenon of gene differentiation in two ecotypes are already appeared in the early growth stage of lotus,because the formation of expanded rhizome is closely related to the metabolism of starch.This study used transcriptome sequencing technology to analyse the genetic differentiation in the early growth stages of temperate lotus and tropical lotus,and speculated candidate genes that may be involved in the adaptive evolution process of two ecotypes.And we found the genes that related to the formation process of temperate lotus rhizome.This result provided a solid theoretical basis for the breeding and cultivation of high-quality lotus seed in the later period.