Phylogenetic Analysis Reveals The Evolution And Diversification Of NBS-LRR Genes In The Nymphaea Colorata

Resistance genes(R genes)are genes in plant genomes that convey plant disease resistance against pathogens by producing R proteins.The main class of R genes consist of a nucleotide binding domains(NBS)and a leucine rich repeat domains(LRR)and are often referred to as NBS-LRR genes.Nymphaea colorata can be widely distributed around the world.The special position of N.colorata in phylogenetic and its wide-ranging ecological adaptability make it both important in evolutionary genetics and ecology.This study provides a systematic phylogenetic analysis,showing that NBS-LRR genes have large duplications in N.colorata.To explore the reasons for the duplications and diversifications through the analysis of conserved domains and chromosome distribution.Finally,combined with the results of analysis of cis-acting elements and tissue expression to characterize the function of NBS-LRR genes.To confirm the result that heightened ability of relatively genetically rich populations to colonize novel habitats.This provides a theoretical basis for the future study of the co-evolutionary relationship between the ecological mechanism and environment in angiosperms.The main results are as following:360 NBS-LRR genes,these represent almost 1.14% of the whole genome of N.colorata and show amount of gene duplicaiton in N.colorata compared with other representative species.NBS-LRR genes can be divided into three subgroups: TNL,RNL and CNL,account for 31.94%,3.06% and 65.00% respectively in N.colorata.Moreover,although TNL has partially duplications in N.colorata,it is lost in Spirodela polyrhiza and Zostera marina which are also aquatic plants.RNL maintains a relatively conservative genetic evolution pattern.And CNL has a significant expansion in N.colorata,which is different from the model plant.It is speculated that the NBS-LRR genes gradually exhibits different subgroups expansions during the evolution process in order to cope with the stress of different growth environments.Base on similarity of sequence,those genes in the same subgroup are almost have the same conserved domains and motifs.Among these,TNL III has the average number of exons was 7.35,and have ratio of 0-phase intron and exon-phase symmetry are 73.96% and 40.83% respectively.This may mean that highly alternative splicing during translation in TNL III genes.And introns have less members on the CNL,which almost have all the coding sequence in the same exons.Predictably,it is relatively conservative and contains large regulatory elements during the evolution.In the prediction of protein structure,it was found that the protein structure of TNL are saddle-like,which may facilitate the interaction of its signal;the protein structure of CNL are loose and it may recognition the site of action.By the relative map position of NBS-LRR genes are shown on each of the 14 chromosomes.It was found that NBS-LRR genes has large duplications in N.colorata may for two reasons: tandem duplications and the whole genome duplicaitons(WGD)to produce paralogous gene.Finally,after analyzing the cis-acting elements of the NBS-LRR genes which have promoter-cis-acting elements involved in light response,defense and stress responsiveness.Can be concluded that NBS-LRR genes play a role in the defense and stress.Moreover,it can be clearly seen that just few genes have high expression level in the carpel form the heat map.Although NBS-LRR genes have large duplications,the expression is low.Likely,it needs external stimuli to express.The accuracy of the RPKM data was verified by qRT-PCR technology.This study reveals the evolutionary history of NBS-LRR genes.Plants produce different regulatory effects through the duplications of NBS-LRR genes to adapt to environmental changes and cope with ecological threats.This conclusion has reference significance and value for the rapid rise of NBS-LRR genes in the N.colorata,and even the whole angiosperms.