Rac regulation of NtrbohD, the oxidase responsible for the oxidative burst in elicited tobacco cell

Five cDNAs encoding Rac protein homologues to the Rho-related proteins from plants (Rop) were isolated in tobacco, and the function of one of them, Ntrac5, was studied. The Ntrac5 mRNA is repressed when tobacco leaves and cells are treated with the fungal elicitor cryptogein. Tobacco cells were transformed with sense constructs of Ntrac5 or Ntrac5V15, encoding the native GTP/GDP-bound form of this Rac protein homologue or the constitutively active mutant in its GTP-bound form, respectively. Immunological studies indicate that the corresponding protein is continuously located on the plasma membrane (PM). Both types of transformed cells show the same extra-cellular alkalinization as the control, but a high decrease in the active oxygen species (AOS) production after elicitation with cryptogein. Moreover, the regulation of NtrbohD, the oxidase involved in AOS production upon elicitation, is affected at both transcriptional and translational levels in cells overexpressing Ntrac5. Thus, Ntrac5 could be considered as a negative regulator of NtrbohD.