Cytoskeleton functions in plant–microbe interactions

The plant cytoskeleton consists of actin filaments and microtubules and plays a pivotal role as mediator of intracellular transport processes. In addition to this essential cellular housekeeping task it significantly contributes to the establishment of cell polarity during plant development and morphogenesis. Rapid changes in regular cytoskeleton architecture occur upon contact of individual plant cells with both pathogenic and symbiotic microbes. In the case of pathogens, polarized cytoskeletal rearrangements are thought to allow the localized delivery of cargo for defense execution, while in symbiotic interactions the reorganization may advance establishment of the symbiotic relationship. Although firm experimental evidence for these facts is lacking to date, it is believed that microbial metabolites and effector proteins are released into plant cells for manipulation of the host cytoskeleton, while some secreted plant defensive polypeptides may target the microbial cytoskeleton. This would be consistent with the recent finding that cytoskeletal functions are not only crucial for plant defense but likewise essential during various stages of microbial pathogenesis. The cytoskeleton thus emerges as a potential mutual target in plant–pathogen combats that appears to be under attack by effector molecules from both sides.