The aphid Acyrthosiphon pisum depends on a bacterial symbiont, Buchnera aphidicola, for amino acids it can't get from plants. The aphid, in turn, provides the bacterium with energy and carbon as well as shelter inside specialized cells.
Such interdependent relationships are not unusual in the natural world. What is unusual, report Helen Dunbar, Nancy Moran, and colleagues in a new study published this week in the open access journal PLoS Biology, is that a single point mutation in Buchnera's genome can have consequences for its aphid partner that are sometimes detrimental, and sometimes beneficial.
The authors probe Buchnera's and A. pisum's ability to tolerate heat. When exposed to high temperatures, Buchnera is supposed to activate special "heat-shock" genes whose products help to protect proteins from heat-related degradation. By using microarrays to assess activity of A. pisum and Buchnera genes, the researchers discovered that after a four-hour exposure to 35 C temperature, some of their laboratory strains of Buchnera upregulated the heat-shock genes, but others did not. Further analysis showed the genetic basis for the difference: a single missing nucleotide in an adenine-filled stretch of DNA, called a promoter, that's involved in activating the heat-shock gene. Testing at a range of temperatures from 15 C to 35 C showed that activation of the heat-shock gene was consistently lower in the lines with the missing nucleotide than in the normal bacteria.
What does this mean for A. pisum's ability to tolerate tough conditions? To answer that, the researchers asked whether exposing juvenile aphid hosts of Buchnera with either long or short promoters to four hours of high temperatures (35 or 38 C) affected their ability to reproduce. They found that few of the aphids with bacteria bearing short promoters reproduced after the heat treatment, while those with bacteria bearing the longer promoters had no trouble. In addition, aphids th
Contact: Natalie Bouaravong
Public Library of Science