The genetic architecture of diet-dependent immune defense in Drosophila. Robert Unckless, Susan Rottschaefer, Brian Lazzaro. Department of Entomology, Cornell University, Ithaca, NY.
The ubiquitous genetic variation may be explained, in part, by heterogeneity in environments experienced by individuals within and between populations. Two fundamental parts of an individual's life are nutrition and immunity and there are several examples of how the two may influence each other. Here we examine the influence of diet on immunity and the genetic basis behind this interaction. We raised flies from the Drosophila Genetic Resource Panel (DGRP) on two diets (high and low sugar), then infected each with Providencia rettgeri and measured bacterial load 24-hours post infection. We also measured several nutritional indices (including glucose, protein, triglycerides and weight) for each line. Flies reared on the high sugar diet had much higher bacterial loads and there was a significant negative correlation between immune response and glucose, but only on the high sugar diet. Genome wide association tests revealed several candidate genes for both immune and nutritional index variation. Immunity candidates were validated using classical mutants. Two genes (crinkled and Indy contained SNPs significant only on the high sugar diet. Interestingly, the crinkled SNPs showed an interaction with the glucose correlation with load with one allele showing a negative correlation between load and glucose and the other no correlation at all. Thus, we show that diet influences immunity in flies and that the genetic basis of this interaction is tractable.