Figure 1. Working hypothesis for the modulation of host resistance and cell signaling through control of actin cytoskeletal dynamics. The virulence activity of the bacterial cysteine protease AvrPphB targets an unidentified kinase that is responsible for the phosphorylation and subsequent regulation of actin depolymerizing factor-4 (ADF4). As a key regulator in controlling not only actin filament organization, but also as a modulator of the balance of globular (G) and filamentous (F) actin, targeting of ADF4 by pathogens represents a key switch in controlling host cell response. At a transcriptional level, the balance of cytoplasmic vs. nuclear actin is required for RNA polymerase function and the general organization and maintenance of chromatin architecture. ETI, effector triggered immunity; PTI, pathogen-associated molecular pattern (PAMP)-triggered immunity; ADF, actin depolymerizing factor; PRF, profilin. This figure was inspired by Vartiainen et al.⁹