Can Actin Depolymerization Actually Result In Increased Plant Resistance To Pathogens?

Introductory paragraphThe integrity of the actin cytoskeleton is essential for plant immune signalling1. Consequently, it is generally assumed that actin disruption reduces plant resistance to pathogen attack2-4. However, in a previous study, it was shown that actin depolymerisation triggers the salicylic acid (SA) signalling pathway5, which is interesting because increased SA is associated with enhanced plant resistance to pathogen attack6,7. Here, we attempt to resolve this seeming inconsistency by showing that the relationship between actin depolymerization and plant resistance is more complex than currently thought. We investigate the precise nature of this relationship using two completely different plant pathosystems: i) a model plant (Arabidopsis thaliana) and a bacterial pathogen (Pseudomonas syringae), and ii) an important crop (Brassica napus) and a fungal pathogen (Leptosphaeria maculans). We demonstrate that actin depolymerization induces a dramatic increase in SA levels and that the increased SA is biosynthesized by the isochorismate synthase pathway. In both pathosystems, this phenomenon leads to increased plant resistance.