Modification of plant R ac/ R op GTP ase signalling using bacterial toxin transgenes

Bacterial protein toxins which modify R ho GTP ase are useful for the analysis of R ho signalling in animal cells, but these toxins cannot be taken up by plant cells. We demonstrate in vitro deamidation of A rabidopsis R op4 by E scherichia coli C ytotoxic N ecrotizing F actor 1 ( CNF 1) and glucosylation by C lostridium difficile toxin B . Expression of the catalytic domain of CNF 1 caused modification and activation of co‐expressed A rabidopsis R op4 GTP ase in tobacco leaves, resulting in hypersensitive‐like cell death. By contrast, the catalytic domain of toxin B modified and inactivated co‐expressed constitutively active R op4, blocking the hypersensitive response caused by over‐expression of active R ops. In transgenic A rabidopsis, both CNF 1 and toxin B inhibited R op‐dependent polar morphogenesis of leaf epidermal cells. Toxin B expression also inhibited R op‐dependent morphogenesis of root hairs and trichome branching, and resulted in root meristem enlargement and dwarf growth. Our results show that CNF 1 and toxin B transgenes are effective tools in R op GTP ase signalling studies.