NADPH oxidases expression pattern determines ROS production in the plant response to pathogen attack
The massive production of reactive oxygen species (ROS), mainly hydrogen peroxide, is one of the earliest plant responses after pathogen attack. These reactive species should occur in a controlled manner in order to function as signals contributing to the activation of plant defenses. In plants, the major enzyme responsible for ROS production after pathogen attack is the NADPH oxidase, an enzyme homologous to the one activated in the animal immune system. Many groups are trying to elucidate how this production of ROS is regulated to fulfill their signaling mission without causing excessive damage to the plant itself.
A recent study analyzes the pattern expression that the two main NADPH oxidase genes in the model plant Arabidopsis thaliana,
RbohF and RbohD, show after attack by pathogens. The study has been led by Dr. Miguel Angel Torres of the Center for Biotechnology and Plant Genomics (CBGP and involves researchers from the Sainsbury Lab (TSL, Norwich, England). The study, published in the Journal of Experimental Botany, used promoter fusions to β-Glucuronidase or Luciferase (LUC) markers that allow localization of the cell types where these genes are expressed. These analyses have established that both genes display a differential pattern of expression after pathogen attack, suggesting that these two genes participate in distinct processes within the activation of plant immunity. Furthermore, a promoter-swap study shows that expression directed by RbohD promoter is needed for this enzyme to produce hydrogen peroxide massively. This suggests that, besides the regulation by calcium and phosphorylation events documented for this enzyme, transcriptional regulation represents an important factor for the precise control of ROS production. In addition, the study of the expression pattern of these genes has allowed to uncover a new function for these pleiotropic oxidases in Arabidopsis basal resistance against not-adapted pathogens.
RbohD promoter is activated after attack by a fungal necrotroph. In vivo luminescence produced in three-week-old pD-LUC and pF-LUC plants, 24 hours after treatment with spores of the fungal necrotroph Plectosphaerella cumumerina (PcBMM, above) and control (below).
Dr. Miguel Angel Torres performs his research within the Plant Innate Immunity and Resistance against Necrotrophic Fungigroup led by Professor Antonio Molina, at the CBGP. These fungi, triggering cell death in plant tissues to gain easy access to nutrients, represent a serious problem for agriculture production. These studies on the signals that mediate the activation of plant defenses can be the starting point for the design of new strategies to fight against these important crop pathogens.