Plastids and pathogens

Abstract

I n bacteria, MscS-type mechanosen- sitive channels serve to protect cells from lysis as they swell during extreme osmotic stress. We recently showed that two MscS homologs from Arabidopsis thaliana serve a similar purpose in the epidermal plastids of the leaf, indicating that the plant cell cytoplasm can present a dynamic osmotic challenge to the plas- tid. MscS homologs are predicted to be targeted to both plastids and mitochon- drial envelopes and have been found in the genomes of intracellular pathogens. Here we discuss the implications of these observations and propose that MS chan- nels provide an essential mechanism for osmotic adaptation to both intracellular and extracellular environments.