The tomato <scp>Arp2/3</scp> complex is required for resistance to the powdery mildew fungus <scp> <i>Oidium neolycopersici</i> </scp>

Abstract The actin‐related protein 2/3 complex (Arp2/3 complex), a key regulator of actin cytoskeletal dynamics, has been linked to multiple cellular processes, including those associated with response to stress. Herein, the Solanum habrochaites ARPC3 gene, encoding a subunit protein of the Arp2/3 complex, was identified and characterized. ShARPC3 encodes a 174‐amino acid protein possessing a conserved P21‐Arc domain. Silencing of ShARPC3 resulted in enhanced susceptibility to the powdery mildew pathogen Oidium neolycopersici ( On ‐Lz), demonstrating a role for ShARPC3 in defence signalling. Interestingly, a loss of ShARPC3 coincided with enhanced susceptibility to On ‐Lz, a process that we hypothesize is the result of a block in the activity of SA‐mediated defence signalling. Conversely, overexpression of ShARPC3 in Arabidopsis thaliana , followed by inoculation with On ‐Lz, showed enhanced resistance, including the rapid induction of hypersensitive cell death and the generation of reactive oxygen. Heterologous expression of ShARPC3 in the arc18 mutant of Saccharomyces cerevisiae (i.e., ∆arc18 ) resulted in complementation of stress‐induced phenotypes, including high‐temperature tolerance. Taken together, these data support a role for ShARPC3 in tomato through positive regulation of plant immunity in response to O . neolycopersici pathogenesis.