EEMB/MCDB Joint Departmental Seminar
Evolutionary assembly of a beetle chemical defense system
Abstract: Biological innovations can arise from the evolution of new cell types that function collectively to generate new, organ-level behaviors. Understanding how new cell types originate and give rise to the emergent properties of organs is a major challenge in biology. Here, we deconstruct the molecular assembly of new cellular functions comprising a biosynthetic innovation in animals. A chemical defense gland in rove beetles (Staphylinidae) is the putative catalyst behind the global radiation of a clade of >16,000 species. Using single cell sequencing to guide genetic interrogation, we show how defense gland function was pieced together from ancestral molecular source material to create two, clade-specific secretory cell types, each capable of synthesizing distinct compound classes. Production of noxious benzoquinones by one cell type derives from tyrosine metabolism, and evolved from a duplication within the laccase family of diphenoloxidases with ancestral roles in exoskeleton formation. Production of a short-chain alkane and two esters by the second cell type evolved from assembly of a multi-enzyme fatty acid pathway; the alkane branch bears identical enzymatic logic to the ancient biosynthesis pathway for insect pheromones, but has been convergently pieced together from enzyme paralogs. The alkane and esters provide a solvent for the benzoquinones, creating a potent, bioactive secretion. By ablating the biosynthesis pathway in either cell type, we demonstrate that this chemical cooperativity confers the adaptive value of the gland. The molecular assembly of each individual cell type has thus been shaped by coevolution between the two cell types—a process driven by natural selection for new, organ-level properties.
Dr. Bruckner is available to meet virtually on the day of the seminar, and will be attending a virtual lunch with graduate students directly after the talk. Please see links in email to sign up.