Ancestral Polyploidy Formation And Gene Conversion Of Citrus Genome

With rich nutrition in fruits,citrus plants have important economic value.The sequencing of genome structure of several citrus plants has been completed successively,including a citrus relative(atalantia)in Rutaceae,which provides an opportunity to study citrus plants and the Rutaceae.By comparatively analyzing the relationships among genomes and within genomes,we deduced the duplicated genes produced by polyploidization(s)and indentified the orthologies between the compared genomes.After than,we performed two colinear lists of citrus plants associated with polyploidization and speciations,which provided an important genomic comparative resource to study the genome evolution and gene functions of citrus plants.Compared with the colinear regions within grape as the out-group,we have found that the colinearity within citrus genomes had been damaged seriously,which was probably caused by gene loss and translocations.In this study,with the counting of gene retention in citrus plants,we found the three well assembled genomes with pretty higher retained genes,up to 65-82%,significantly more than eudicots affected by extra polyploidizations;and we found that gene loss within citrus plants was an random evolution event and the scales of colinear genes suffered gene loss almost satisfied with a certain geometric distribution.Besides,we inferred the time of polypliodizaiton(s)suffered in citrus,re-dated major evolutionary events during their evolution by performing evolutionary rate correction,and found that sweet orange evolved fastest in the citrus plants.We also deduced the split nodes between different species and found that the divergence between grape and citrus plants was about 81-91 million years ago(mya),among which the divergences between citrus plants were less than 10 mya.Furthermore,we identified the families of genes related to vitamin C(VC)synthesis in citrus plants and determined that the genes associated with the core-eudicot-common hexaploidy ECH events accounted for about half of the genes related to VC.Moreover,with the constructed quartets model of homologous genes between grape and each of citrus plants,we explored gene conversion(GCV)in citrus plants and found a certain scale of GCV in citrus plants,genes suffered GCV prefering to locate on the terminal of chromosome and GC content without significant difference compared with other genes.Finally,this study provides an important comparative genomics resource for understanding the evolution of citrus,even to Rutaceae plants,and the innovation of gene function.Figure 19;Table 9;Reference 52...