l e t t e r sHow an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants 1 , but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood 2 . We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management.The global pest P. xylostella (Lepidoptera: Yponomeutidae) is thought to have coevolved with the crucifer plant family 3 ( Supplementary Fig. 1) and has become the most destructive pest of economically important food crops, including rapeseed, cauliflower and cabbage 4 . Recently, the total cost of damage and management worldwide was estimated at $4-5 billion per annum 5,6 . This insect is the first species to have evolved resistance to dichlorodiphenyltrichloroethane (DDT) in the 1950s 7 and to Bacillus thuringiensis (Bt) toxins in the 1990s 8 and has developed resistance to all classes of insecticide, making it increasingly difficult to control 9,10 . P. xylostella provides an exceptional system for understanding the genetic and molecular bases of how insect herbivores cope with the broad range of plant defenses and chemicals encountered in the environment (Supplementary Fig. 2).We used a P. xylostella strain (Fuzhou-S) collected from a field in Fuzhou in southeastern China (26.08 °N, 119.28 °E) for sequencing ( Supplementary Fig. 1). Whole-genome shotgun-based Illumina sequencing of single individuals (Supplementary Table 1), even after ten generations of laboratory inbreeding, resulted in a poor initial assembly (N50 = 2.4 kb, representing the size above which 50% of the total length of the sequences is included), owing to high levels of heterozygosity ( Supplementary Figs. 3 and 4 and Supplementary Table 2). Subsequently, we sequenced 100,800 fosmid clones (comprising ~10× the genome length) to a depth of 200× ( Supplementary Fig. 5 and Supplementary Tables 3-5), assembling the resulting sequence data into 1,819 scaffolds, with an N50 of 737 kb, spanning ~394 Mb of the genome sequence (version 1; Supplementary Fig. 6 and Supplementary Table 6). The assembly covered 85.5% of a set of protein-coding ESTs (Supplementary Tables 7 and 8) generated by transcriptome sequencing 11 . Alignment of a subject scaffold against a 126-kb BAC (GenBank GU058050) from an altern...

Cytochrome P450 monooxygenases are present in almost all organisms and can play vital roles in hormone regulation, metabolism of xenobiotics and in biosynthesis or inactivation of endogenous compounds. In the present study, a genome-wide approach was used to identify and analyze the P450 gene family of diamondback moth, Plutella xylostella, a destructive worldwide pest of cruciferous crops. We identified 85 putative cytochrome P450 genes from the P. xylostella genome, including 84 functional genes and 1 pseudogene. These genes were classified into 26 families and 52 subfamilies. A phylogenetic tree constructed with three additional insect species shows extensive gene expansions of P. xylostella P450 genes from clans 3 and 4. Gene expression of cytochrome P450s was quantified across multiple developmental stages (egg, larva, pupa and adult) and tissues (head and midgut) using P. xylostella strains susceptible or resistant to insecticides chlorpyrifos and fiprinol. Expression of the lepidopteran specific CYP367s predominantly occurred in head tissue suggesting a role in either olfaction or detoxification. CYP340s with abundant transposable elements and relatively high expression in the midgut probably contribute to the detoxification of insecticides or plant toxins in P. xylostella. This study will facilitate future functional studies of the P. xylostella P450s in detoxification.

We present here the de novo assembly and annotation of the transcriptome of Plutella xylostella (diamondback moth (DBM)), a widespread destructive pest of cruciferous plants, using short reads generated by Illumina sequencing from different developmental stages and insecticide-resistant strains. A total of 171,262 non-redundant sequences, denoted as unigenes, were obtained. They represented approximately 100-fold of all DBM mRNA and EST sequences in GenBank thus far. We identified 38,255 unigenes highly similar to the known functional protein-coding genes, most of which were annotated using gene ontology (GO) and orthologous groups of proteins (COG). Global profiling of differentially expressed unigenes revealed enriched GOs and biological pathways that were related to specific developmental stages and insecticide resistance. We also evaluated the resistance-related single nucleotide polymorphism (SNP) using this high-throughput genotyping method. The newly developed transcriptome will facilitate researches on the DBM developmental biology and insecticide resistance evolution, and ultimately provide better pest management systems.