Molecular and evolutionary bases of Pieris butterflies for overcoming diverse chemical defenses in their host plants

In terrestrial ecosystems, plants and herbivorous insects account for more than half of the described species and play quite important ecological roles. Plants and herbivorous insects have strong chemical interaction as plants defend themselves with various defense compounds such as secondary metabolites and herbivores adapt to it by evolving detoxification mechanisms. Larvae of Pieris butterflies feed on Brassicaceae plants as the main host. Brassicaceae plants contain diverse glucosinolates (GLS) as a main chemical defense, which can be rapidly hydrolyzed into toxic isothiocyanates by a plant enzyme called myrosinase upon tissue damage. Larvae of Pieris butterflies are known to express nitrile-specifier protein in their gut and this can redirect toxic breakdown products of GLSs to less toxic metabolites. Although NSP is considered an evolutionary key innovation for Pieridae that enabled these butterflies to colonize GLS-containing plants, it has been largely unclear whether NSP is enough for Pieris butterfly larvae to overcome the diverse types of GLS they encounter in their host plants. In this seminar, I would like to introduce our recent findings showing that Pieris butterfly larvae not only use NSP but also use its ortholog major allergen (MA) to overcome the diverse types of GLS in their Brassicaceae host plants. We found that Pieris larvae show fine-tuned regulation of those two adaptive genes depending on the chemical profiles of their host plants. Furthermore, those two adaptive genes have different evolutionary trajectories in macro- and micro-evolutionary scales among Pieris species or populations associated with their pattern of host plant usage. Moreover, with an approach using CRISPR/Cas9 genome editing, we showed that both NSP and MA have different but complementary roles in disarming GLS-based defenses in their host plants and that both genes are crucial for Pieris in overcoming their host plant’s major chemical defense. Those highlight that having both NSP and MA is a key for Pieris butterflies to overcome the diverse types and GLS and, consequently, adapt to a wider range of Brassicaceae hosts. Our results illuminate that gene duplication, functional differentiation, and the evolution of gene regulation mechanisms are all crucial for herbivorous insects to overcome co-evolving chemical defenses in their host plants.