Abstract
Heat shock protein 83 (HSP83) is homologous to the chaperone HSP90. It has pleiotropic functions in Drosophila melanogaster, including the control of longevity and fecundity, and facilitates morphological evolution by buffering cryptic deleterious mutations in wild populations. In the pea aphid Acyrthosiphon pisum, HSP83 expression is moderately induced by bacterial infection but upregulated more strongly in response to heat stress and fungal infection. Stress-inducible heat shock proteins are of considerable evolutionary and ecological importance because they are known to buffer environmental variation and to influence fitness under non-optimal conditions. To investigate the functions of HSP83 in viviparous aphids, we used RNA interference to attenuate its expression and studied the impact on complex parameters. The RNA interference (RNAi)-mediated depletion of HSP83 expression in A. pisum reduced both longevity and fecundity, suggesting this chaperone has an evolutionarily conserved function in insects. Surprisingly, HSP83 depletion reduced the number of viviparous offspring while simultaneously increasing the number of premature nymphs developing in the ovaries, suggesting an unexpected role in aphid embryogenesis and eclosion. The present study indicates that reduced HSP83 expression in A. pisum reveals both functional similarities and differences compared with its reported roles in holometabolous insects. Its impact on aphid lifespan, fecundity, and embryogenesis suggests a function that determines their fitness. This could be achieved by targeting different client proteins, recruiting distinct co-chaperones or transposon activation.
Highlights
Heat shock proteins (HSPs) are evolutionarily conserved chaperones whose predominant function is to prevent the misfolding and denaturation of proteins caused by environmental stressors such as heat, toxins, or pathogens (Johnson 2012)
The postulated evolutionary and ecological role of HSPs predicts that their expression is induced by exposure to environmental stressors and influences fitness parameters such as lifespan and fecundity (Sorensen et al 2003)
Exposure to mild heat shock or microbial elicitors of immune responses only moderately induced the expression of hsp90 and its homolog hsp83 in the model insects T. castaneum (Freitak et al 2012) and A. pisum (Gerardo et al 2010)
Summary
Heat shock proteins (HSPs) are evolutionarily conserved chaperones whose predominant function is to prevent the misfolding and denaturation of proteins caused by environmental stressors such as heat, toxins, or pathogens (Johnson 2012) Their functions in Drosophila melanogaster are associated with the. In the beetle Tribolium castaneum, another holometabolous model insect, HSP83, which belongs to the HSP90 family, is expressed in the whole body as well as in the oocytes where it is located in the follicle cells. There it is differently expressed during different stages of oogenesis (Xu et al 2010) and in response to heat shock (Xu et al 2009). A phylogenetic analysis of arthropod HSP90 genes reveals that the sequences cluster according to their taxonomic order, with holometabolous and hemimetabolous species showing clear separation (Knorr and Vilcinskas 2011)
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