The elicitor cryptogein blocks glucose transport in tobacco cells

Cryptogein is a 10-kD protein secreted by the oomycete Phytophthora cryptogea that induces a hypersensitive response on tobacco (Nicotiana tabacum var. Xanthi) plants and a systemic acquired resistance against various pathogens. The mode of action of this elicitor has been studied using tobacco cell suspensions. Our previous data indicated that within minutes, cryptogein signaling involves various events including changes in ion fluxes, protein phosphorylation, sugar metabolism, and, eventually, cell death. These results suggested that transport of sugars could be affected and, thus, involved in the complex relationships between plant and microorganisms via elicitors. This led us to investigate the effects of cryptogein on glucose (Glc) uptake and mitochondrial activity in tobacco cells. Cryptogein induces an immediate inhibition of Glc uptake, which is not attributable to plasma membrane (PM) depolarization. Conversely, cryptogein-induced valine uptake is because of PM depolarization. Inhibition of the PM Glc transporter(s) was shown to be mediated by a calcium-dependent phosphorylation process, and is independent of active oxygen species production. This inhibition was associated with a strong decrease in O-2 uptake rate by cells and a large mitochondrial membrane depolarization. Thus, inhibition of Glc uptake accompanied by inhibition of phosphorylative oxidation may participate in hypersensitive cell death. These results are discussed in the context of competition between plants and microorganisms for apoplastic sugars.