Mendel University in Brno 

Leontovyčová H [a, b, c], Trdá L [b], Kalachova T [a, b], Nečasová L [b], Dobrev P I [b], Pospíchalová R [b], Malínská K [a], Burketová L [a, b], Valentová O [], Janda M []

[a] University of Chemistry and Technology Prague, Technicka 5, 166 28 Prague 6, Czech Republic
[b] Institute of Experimental Botany of the Czech Academy of Sciences, Rozvojova 263, 165 02, Prague 6, Czech Republic
[c] Faculty of Science, Charles University in Prague, Faculty of Science, 128 44 Hlavova 2030/8, Prague 2, Czech Republic

Actin cytoskeleton integrity is necessary for immune response upon pathogen attack, both by providing physical barrier and by its involvement in transport of callose, antimicrobial compounds and cell wall components to the infection site. Regarding these facts it has been generally assumed that desintegration of actin cytoskeleton results in enhanced plant susceptibility to pathogens.
However, we have shown that pharmacological actin depolymerization induces the salicylic acid (SA) signalling pathway which contributes to increased plant resistance. We attempt to investigate this apparent inconsistency and show that the relationship between actin depolymerization and plant resistance is more complex than previously thought. After actin depolymerization we observed high increase in the concentration of SA which in this case is biosynthesized via the isochorismate synthase (ICS) pathway. These effects were observed in two different pathosystems: i) Arabidopsis thaliana x Pseudomonas syringae and ii) Brassica napus x Leptosphaeria maculans. In both pathosystems, actin depolymerization activated the SA pathway, leading to increased plant resistance. Timing of the SA pathway activation is crucial for induction of the resistance. To our best knowledge, we herein provide the first direct evidence that disruption of the actin cytoskeleton can lead to increased plant resistance to pathogens, and that SA is vital to this process.