Abstract
Classical evolutionary studies of protein-coding genes have established that genes in the canonical immune system are often among the most rapidly evolving within and between species. As more genomes and transcriptomes across insects are sequenced, it is becoming clear that duplications and losses of immune genes are also a likely consequence of host-pathogen interactions. Furthermore, particular species respond to diverse pathogenic challenges with a wide range of challenge-specific responses that are still poorly understood. Transcriptional studies, using RNA-seq to characterize the infection-regulated transcriptome of diverse insects, are crucial for additional progress in understanding the ecology and evolution of the full complexity of the host response.
Highlights
Genes involved in immune defense have long been recognized as hotspots for rapid evolution in many organisms including insects [1,2]
In Drosophila, early population genetic [3,4] and comparative genomic [5,6] studies demonstrated that key components of the innate immune system experienced substantially more adaptive protein evolution than typical genes in the genome
While Drosophila has received the most research attention, evidence for positive selection in insect immune genes is common in other groups as well [9,10,11]
Summary
Genes involved in immune defense have long been recognized as hotspots for rapid evolution in many organisms including insects [1,2]. Troha and colleagues [70] infected D. melanogaster with ten different bacterial species across a range of pathogenicity, including several bacterial strains that have been recovered from wild fruit flies, and used RNA-seq to measure the transcriptional response to infection They showed that, while a core of canonical immune genes are induced in most conditions, a substantial number of consistently regulated genes were involved in cellular and metabolic homeostasis, some of which may have functions related to immune tolerance [76], while others may reflect physiological consequences of infection. Initiatives such as the i5K project [86] and declining sequencing costs are rapidly increasing the number of assembled insect genomes available, and new approaches such as Tag-seq [87], in which only a short tag for each gene is sequenced, are making large-scale sequencing experiments including adequate replication increasingly feasible
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