Genetic Mapping Of Resistance To Bacillus Thuringiensis Cry1Ac Toxins In Plutella Xylostella

The diamondback moth,Plutella xylostella(L.),is a cosmopolitan pest of cruciferous crops.The entomopathogenic Gram-positive bacterium,Bacillus thuringiensis(Bt),produces diverse insecticidal crystal proteins(ICP)during sporulation,which is widely used to control agricultural pest due to its highly specific activity and environmental safety.However,massive use of Bt pesticides and Bt crops represents high and persistent selection pressure for insect resistance evolution.Unraveling the molecular resistance mechanism is important for sustainable utilization of Bt and integrated pest manage.Our prior work revealed that 20-hydroxyecdysone(20E)and juvenile hormone(JH)can activate MAPK4K4,which is an upstream gene of MAPK signaling pathway inside of the multigenic resistance locus to Bt(BtR-1),trans-regulates expression of many resistance genes and causes resistance to Cry1Ac in P.xylostella.The molecular mechanism of Bt resistance in our resistant strain has no genetic basis.In this study,we mapped major locus conferring resistance to Bt in P.xylostella.The data obtained from whole genome resequencing of 100 P.xylostella pupae from susceptible strain DBM1Ac-S and resistant strain NIL-R was used to perform variant calling,phylogenetic analysis,principal component analysis and Genome-wide association study.Due to the genome without any assembled chromosomes information,we identified 953 SNPs in 34 scaffolds and 390 InDels in 29 scaffolds significantly associated with Bt Cry1Ac resistance.Based on the linkage maps in previous studies and the new genome assembly of P.xylostella,we aligned the scaffolds containing significant variants to scaffold NW-024010942.According to the biphasic nature of genetic linkage,we constructed a backcross line and cloned the informative SNP markers in 186 backcross offspring which were survived from Cry1Ac toxin treatment.Therefore,we mapped the resistance linkage region in the 0.91Mbp of scaffold NW-024010942,which contained ABC transporter family gene and MAP4K4 gene.Based on the above research,we identified the linkage region and candidate genes for resistance to Bt Cry1Ac in diamondback moth,which laid a foundation for further investigating the exact mutation for Bt Cry1Ac resistance.