Adaptive Evolution And Genetic Mechanism Analysis Of Rhizome Enlargement Of Lotus(Nelumbo Nucifera)

Lotus is an ancient dicotyledon plant and has a long history of cultivation and cultivation in China.Lotus is one of the main aquatic ornamental plants,and it can also be used as medicinal plants and vegitables.With the release of lotus genome information,further researchis feasibly on the mechanism of lotus development in the whole genome level.Lotus rhizome is a favorite aquatic vegetable in China,hence,has high economic value.Study focusing the enlargement of lotus rhizome is not only important for basic science but also helpful to the breeding of lotus.In this research,we selected 18 lotus germplasm resources,using the whole genome sequencing method,to explore genetic differentiation pattern of lotus germplasmat the whole genome level.Meanwhile,a F2 genetic population was constructed through crossing between Zhouou(male parent;the temperate lotus with enlargement rhizome,and Donghonghua,the tropical lotus with nonenlargement rhizome.Based on GBS sequencing technology,a largenumber of SNP and polymorphism SSR markers between two parents were determined and used to construct a high-density genetic linkage map of F2 lotus population.In the end,QTL analysis of lotus rhizome phenotypes was conducted to investigate the development mechanism of lotus rhizomes based on the two years rhizome phenotypic data of the F2 population.The main results are as follows:1)Based on the whole genome resequencing data of the 18 germplasm,the genetic differentiation of different subgroups of lotus was analyzed.The genetic distance of N.Lutea Pers.and N.Nucifera Gaertan.is higher than intraspecific of N.Nucifera Gaertan.Temperate wild lotus and tropical lotus have high genomic diversity;the genetic distance between rhizome lotus and temperate wild lotus is close.There is a genomic mixture between flower lotus,seed lotus and tropical lotus.2)Based on analysis of genetic differentiation patterns of the genes between two lotus ecotypes,4603 genes were selected.Those most conserved genes(MR<1.5724)were enriched in GO terms such as gene expression,regulation of RNA metabolic process,among others.Genes with low MR(1.57240<MR≤3.4388)were enriched in the GO terms,including carbohydrate biosynthetic and metabolic process,alcohol metabolic process,and so forth.Genes which have a fast evolution and with high mutation rate(3.4388<MR≤6.3132)were enriched in GO terms such as molecular transducer activity.The genes with very high mutation rate(MR>6.313)were focus on NADH dehydrogenase activity.3)NB-ARC gene family exhibited the highest ratio of family members with loss-of-function mutation,followed by Cytochrome P450.Gene trans.cription related gene families,such as Ring finger,Helix-loop-helix DNA binding,Myb-likes,and AP2 domain genes showed relatively lower ratio of loss-of-function mutations.4)Based on lotus Fa population and GBS sequencing technology,a high-density genetic linkage map was constructed with a total of 1256 markers.There are eight linkage groups,which isin accord with the number of lotus chromosomes.Total distance of the linkage map is 1576.98 cM.The genetic distance of the largest linkage groupand shortest linkage group is 378.87 cM,109.46 cM,respectively.The maximum genetic distance between the two adjacent markers is 16.04 cM,the minimum genetic distance is 3.88 cM and the average genetic distance is 1.35cM.5)Statistics analysis of two years rhizome phenotypic data showed that enlargement index(El)of lotus rhizome and intemode length(IL)are negative correlation significantly;internode perimeter(IP)and weight of single lotus root(SRW)and total weight of lotus rhziome(TW)have significantly positive correlation.The maximum internode length(IL)has a significant negative correlation with the maximum internode perimeter(IP).The maximum rhizome internode perimeter(IP)is positively correlated with the single lotus rhizome weight(SRW)and total weight(TW).The total number of rhizome(RN)is positively correlated with the total weight(TW)of rhizome.There is a significant positive correlation between single lotus root weight and total weight.6)Combing the data from germplasm resequencing and genetic population QTL mapping,a total of 374 genes related lotus rhizome development were selected.Some genes were found to be associated with flowering period,indicating that there was a correlation between the rhizome developement and flowering period.This is the first study on the enlargement of lotus rhizome through natural population resequencing and genetic population QTL mapping strategy.The results will benefit further studies on the molecular mechanisms underlying the enlargement of lotus rhizome.