Role of Glutathione S-transferase D1 in cactus host adaptation
Members of the Glutathione S-transferase gene family have been known to play a role in detoxification in many taxa, including insects. A gene with high homology to the D. melanogaster Glutathione S-transferase-D1 (GstD1) locus was differentially expressed in a Baja California D. mojavensis isofemale line as a response to utilizing an alternative host (S. thurberi) (Matzkin et. al 2006). In both D. melanogaster and in Anopheles gambiae, GstD1 has been implicated in the resistance of these species to the insecticide DDT. I have examined the pattern of sequence variation of the GstD1 locus from all four D. mojavensis opulations, D. arizonae (its sister species) and D. navojoa (outgroup) (Matzkin 2008). The data suggest that in the Baja California and Sonora population of D. mojavensis GstD1 has gone through a period of adaptive amino acid evolution as reflected by the ratio of silent to replacement fixations and polymorphisms. Polarizing these data using D. navojoa indicates that the positive selection occurred in the lineage leading to these D. mojavensis populations. Further analyses indicate that of the seven amino acid fixations that occurred in the D. mojavensis lineage two of them occur in the active site pocket, potentially having a significant affect on substrate specificity and possibly in the adaptation to alternative cactus hosts (Matzkin 2008). Currently we have heterologously expressed GSTD1 and have begun to access the functional and kinetic differences associated with the amino acid substitutions observed between the different host populations as well as generating CRISPR KO (Sanders et al. in prep).
Functional analysis of the Alcohol Dehydrogenase paralogs in D. mojavensis and D. arizonae
Alcohol dehydrogenase (Adh) in D. mojavensis and D. arizonae is a great example of subfunctionalization, were these species have a pair a paralogs (Adh-1 and Adh-2) that perform a similar set of functions as in species which have only have a single functional copy (eg. D. melanogaster) (Matzkin and Eanes 2001; Matzkin 2004). We have previously described how the Adh paralogs in these flies, whose expression is non-overlapping, have distinct biochemical properties (Matzkin 2005). Currently, we are generating CRISPR KO of both paralogs to better assess the functional role of Adh-1 and Adh-2 in cactus host adaptation (Milder et al. in prep).