| The diamondback moth(DBM),Plutella xylostella(L.)is a specialist of crucifers,which has been threatening the safety in production of cruciferous crops,and the total cost of damage and management of the DBM worldwide is estimated at US$4-5 billion annually.Better understanding of the genetic and molecular regulatory mechanisms of the important biological traits of DBM，such as insecticide resistance,food preference and long-distance migration,will provide scientific basis for the effective control and sustainable management of this insect pest in the practice.Accompanying the decoding of the DBM genome,DBM functional genomics has been launched.Therefore,construction of a genetic linkage map of high density in the DBM will facilitate the building of fine genome sequence and genetic mapping of the target genes,which will accelerate the isolation and decipherment of the important functional genes.For the first time in insect genomics,we used the next-generation sequencing-based whole genome resequencing approach for the construction of a genetic linkage map in DBM based on our established DBM genome reference sequence.Through sequencing individuals of the parents and back-cross progeny,we developed approximately 1 million SNP makers for each of the DBM individuals tested.Further work was conducted to screen for the informative SNP markers and to calculate their segregation patterns in the back-cross progeny for establishing linkage relationship and genetic distance among markers.In total,we integrated 2672 informative SNP markers onto the 34 genetic linkage groups,which was 3 more than the known chromosome number in DBM(n=31)and 10 times of the informative markers of the genetic linkage groups built using RAD-seq.We mapped 375 genome scaffolds with a total length of 237.27 Mb onto the corresponding linkage groups accounting for 68.93%of the genome size.For the full gene set annotated from DBM genome assembly,478 genes were covered by 833 informative SNP markers of the genetic linkage map,and 238 of these SNP markers were localized on the coding sequences.Syntenic analysis between the genomes of DBM and silkworm(Bombyx mori)at the protein level identified 453 syntenic blocks.Some of the blocks were highly conservative and some of the blocks were structurally different from each other.Through comparing the syntenic region at the chromosome level,we proposed that chromosomes 4,5 and 8 of silkworm could be the result of chromosomal fusion of the DBM.Our results were inconsistent with the previous findings that chromosomes 11,23 and 24 of silkworm could be the result of chromosomal fusion of the DBM.Further work with in situ hybridization between the chromosomal fragments of the DBM and silkworm is necessary for clarifying their relationship.To explore the specific gene members of each species,we constructed the gene families among the DBM,silkworm and butterfly(Danaus plexippus).We identified the species-specific transcription factors and gene members that were involved with xenobiotic detoxification,chemoreception,food digestion and immune responses,etc.These findings revealed that the differences in the morphology,behavior and physiological characteristics of the different lepidopteran species are regulated by a complex gene network and their regulatory factors,which may have evolutionarily originated from the natural selection of comprehensive genomic changes imposed by external environmental factors.The construction of the DBM genetic linkage map of high density was another important after completion of the DBM genome and transcriptome projects,which will definitely promote DBM functional genomics studies and pave a theoretical way for the DBM control and insecticide resistance management based on its biological traits. |
