Untitled

Abstract

Environmental response genes are defined as those encoding proteins involved in interactions external to the organism, including interactions among organisms and between the organism and its abiotic environment. The general characteristics of environmental response genes include high diversity, proliferation by duplication events, rapid rates of evolution, and tissue- or temporal-specific expression. Thus, environmental response genes include those that encode proteins involved in the manufacture, binding, transport, and breakdown of semiochemicals. Postgenomic elucidation of the function of such genes requires an understanding of the chemical ecology of the organism and, in particular, of the "small molecules" that act as selective agents either by promoting survival or causing selective mortality. In this overview, the significance of several groups of environmental response genes is examined in the context of chemical ecology. Cytochrome P-450 monooxygenases provide a case in point; these enzymes are involved in the biosynthesis of furanocoumarins (furocoumarins), toxic allelochemicals, in plants, as well as in their detoxification by lepidopterans. Biochemical innovations in insects and plants have historically been broadly defined in a coevolutionary context. Considerable insight can be gained by defining with greater precision components of those broad traits that contribute to diversification. Molecular approaches now allow chemical ecologists to characterize specifically those biochemical innovations postulated to lead to adaptation and diversification in plant/insect interactions.

Studies on <i>Aphis gossypii</i> cytochrome P450s CYP6CY22 and CYP6CY13 using an <i>in vitro</i> system

“…In insects, members of the CYP4, -6, -9, and -12 families are implicated in biological detoxifying functions in the environment, and members of the CYP4 and CYP6 subfamilies are most commonly involved in the metabolism of and resistance to xenobiotics. 29,30) The CYP6CY22 (c21228_g1) gene was overexpressed 46-fold in the KR clone, as compared with the NS clone, and 4-fold, as compared with the MS clone when aphids were treated without acetamiprid. Similarly, the CYP6CY13 (c21368_g1) gene was expressed at a 7-fold higher level by the KR clone vs. the NS clone and a 3-fold higher level by the KR clone vs. the MS clone under the same conditions.…”

The genetic basis of a plant–insect coevolutionary key innovation

“…Papilio butterfly species diversity increases with host plant furanocoumarin diversity (11). Interestingly, furanocoumarins both induce and are detoxified by Papilio species using other members of the cytochrome P450 superfamily (68). Cytochrome P450 participation on both sides of the plant-insect interaction highlights the diverse functional roles members of this gene superfamily play in environmental response (68).…”

Resolution of the insect ouabain paradox

“…Historically, this has been explained by several mechanisms, such as detoxification (1,2), direct excretion (3), or storage excretion (4), sometimes coupled by active resorption of the toxin (3). In some cases, critical residues in target proteins have been found to have mutated to confer resistance (5).…”