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Abstract:
Antagonistic chemical interactions between herbivorous insects and their host plants are often thought to co-evolve in a stepwise process, with an evolutionary innovation on one side being countered by a corresponding advance on the other. Glucosinolate sulfatase (GSS) enzyme activity is essential for the Diamondback moth (DBM), Plutella xylostella, to overcome a highly diversified secondary metabolite-based host defense system in the Brassicales. GSS genes are located in an ancient cluster of arylsulfatase-like genes, but the exact roles of gene copies and their evolutionary trajectories are unknown. Here, we combine a functional investigation of duplicated insect arylsulfatases with an analysis of associated nucleotide substitution patterns. We show that the DBM genome encodes three glucosinolate sulfatases with distinct substrate spectra and distinct expression patterns in response to glucosinolates. Contrary to our expectations, early functional diversification of gene copies was not indicative of a co-evolutionary arms race between host and herbivore. Instead, both copies of a duplicated arylsulfatase gene evolved concertedly in the context of an insect host shift to acquire novel detoxifying functions under positive selection, a pattern of duplicate gene retention that we call ‘concerted neofunctionalization’.
