Plants are constantly being attacked by fungi, bacteria, or other types of parasites. As a result, they have developed adaptive responses that enhance their survival. These pathogens produce a specific class of molecules—called elicitors—that plants recognize: elicitors trigger plant resistance mechanisms. “If we want to control this defense mechanism, we need a better understanding of how it is activated,” says Associate Professor Patricia Gerbeau-Pissot. She continues, “For this reason, we have been looking at plant cell plasma membranes, to determine the role they play in the early stages of plant defense.”
The cell membrane is made up of two lipid layers into which proteins are inserted. Gerbeau-Pissot explains, “Thanks to the development of an innovative imaging technique, we have been able to show, for the first time, that the plant plasma membrane is not a uniform structure. Rather, it is a heterogeneous mosaic of many tiny territories.” These territories, called microdomains, contain varying levels of particular categories of proteins and lipids. Microdomains with higher levels of these molecules are more rigid and ordered because strong interactions take place among the components, the lipids in particular.
When cells are exposed to an oomycete elicitor, crytogein, their plasma membranes undergo changes within minutes. These early changes include, on the one hand, an increase in overall membrane fluidity; on the other hand, highly localized regions become more rigid as a result of an increase in the proportion of ordered microdomains. Interestingly, when cells are exposed to a different, bacterial elicitor, flagelline, their membranes only demonstrate the latter reaction.
The difference in the responses provoked by the two elicitors stems from a difference in their properties. Crytogein, in contrast to flagelline, causes necrosis: plants respond to its presence by allowing localized cell death in order to slow its advancement.
These results therefore give rise to the hypothesis that the increase in ordered microdomains, which is provoked by both elicitors, is a generic response that is linked to the activation of plant defense mechanisms. In contrast, the increase in fluidity, which is solely elicited by cryogein exposure, is specifically associated with cell death.
These findings suggest that the way in which the plasma membrane perceives signals could shape cellular responses, depending on how the membrane reacts and modifies its microstructure. The mechanisms by which these structural changes are translated into defense responses remain to be uncovered. This research has resulted in a description of plant cell membrane architecture that provides a novel degree of detail. It also illustrates the dynamic processes taking place in the membrane during defense-related cell signaling.
- Gerbeau-Pissot P, Der C, Thomas D, Anca IA, Grosjean K, Roche Y, Perrier-Cornet JM, Mongrand S and Simon-Plas F. 2014. Modification of plasma membrane organization in tobacco cells elicited by cryptogein. Plant Physiology 164 (1):273-86.
- Simon-Plas F, Perraki A, Bayer E, Gerbeau-Pissot P, Mongrand S. 2011. An update on plant membrane rafts. Curr Opin Plant Biol 14 (6):642-9