Abstract
The Small Cabbage White ( Pieris rapae) is originally a Eurasian butterfly. Being accidentally introduced into North America, Australia, and New Zealand a century or more ago, it spread throughout the continents and rapidly established as one of the most abundant butterfly species. Although it is a serious pest of cabbage and other mustard family plants with its caterpillars reducing crops to stems, it is also a source of pierisin, a protein unique to the Whites that shows cytotoxicity to cancer cells. To better understand the unusual biology of this omnipresent agriculturally and medically important butterfly, we sequenced and annotated the complete genome from USA specimens. At 246 Mbp, it is among the smallest Lepidoptera genomes reported to date. While 1.5% positions in the genome are heterozygous, they are distributed highly non-randomly along the scaffolds, and nearly 20% of longer than 1000 base-pair segments are SNP-free (median length: 38000 bp). Computational simulations of population evolutionary history suggest that American populations started from a very small number of introduced individuals, possibly a single fertilized female, which is in agreement with historical literature. Comparison to other Lepidoptera genomes reveals several unique families of proteins that may contribute to the unusual resilience of Pieris. The nitrile-specifier proteins divert the plant defense chemicals to non-toxic products. The apoptosis-inducing pierisins could offer a defense mechanism against parasitic wasps. While only two pierisins from Pieris rapae were characterized before, the genome sequence revealed eight, offering additional candidates as anti-cancer drugs. The reference genome we obtained lays the foundation for future studies of the Cabbage White and other Pieridae species.
Highlights
The Small Cabbage White (Pieris rapae, Figure 1), known as European Cabbage Butterfly, or Imported Cabbageworm, is one of the most common and widely spread butterflies in North America, ranging from Southern Canada to Mexico1
North American populations of the Cabbage Whites, currently numbering in billions, are likely a progeny of a single female accidentally introduced to Quebec, Canada during the second half of the 19th century4,5
The reference genome we obtained lays the foundation for future studies of the Cabbage White and other species of Pieridae
Summary
The Small Cabbage White (Pieris rapae, Figure 1), known as European Cabbage Butterfly, or Imported Cabbageworm, is one of the most common and widely spread butterflies in North America, ranging from Southern Canada to Mexico. In addition to damaging plants, caterpillars contaminate and stain produce with feces These butterflies are a source of a protein with anti-cancer properties. These butterflies are a source of a protein with anti-cancer properties10 Termed pierisin, this enzyme of a probable bacterial origin is unique to Pieris and its close relatives among Lepidoptera species. Evolutionary, and biochemical studies of the Cabbage White, we sequenced and annotated its complete genome from North American specimens. The Pieris genome contains a large number of SNP-free segments that are at least 1000 bp long (with the median length equal to 38000 bp), which together constitute 18.3% of the assembled genome This number is below 4% in other species.
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