The role of reactive oxygen species in the virulence of wheat leaf rust fungus Puccinia triticina
Wang, X., Che, M.Z., Khalil, H.B., McCallum, B.D., Bakkeren, G., Rampitsch, C., Saville, B.J. (2020). The role of reactive oxygen species in the virulence of wheat leaf rust fungus Puccinia triticina. Environmental Microbiology, [online] 22(7), 2956-2967. http://dx.doi.org/10.1111/1462-2920.15063
Plain language summary
ROS, or Reactive Oxygen Species are a suite of highly damaging oxygen molecul species that play an important role during the infection of a host plant by a pathogen, and are often an indication of induced host defense responses. In this study, we demonstrate for the first time that the leaf rust fungus, Puccinia triticina (Pt), generates ROS during its infection of its wheat host plant. We experiment with chemical compounds that inhibit various known mechanisms of ROS production and could show that these various Reactive Oxygen Species are critical for the spores of this fungus to germinate when they land on the wheat leaf surface, and for the subsequent infection. These processes are inhibited when using these chemical compounds. By performing a large-scale analysis comparing different stages of the infection, we identified 291 fungal genes that are potentially responsible for the various known mechanisms of ROS production. Thirty-seven of these genes produce known proteins and we could show that the fungus uses five of them (named PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod) when its spores germinate just before the infection. A bit later, when infecting the wheat leaves, the expression of four genes (PtNoxA, PtNoxB, PtNoxR and PtCat) is switched off, meaning they are less likely to play a role during that phase of the infection. However, the expression of PtSod is increased up to 120 hours after infection, showing its further importance. We conclude that these Reactive Oxygen Species play a critical role for the full virulence of this fungus, but that a reduction one ROS compound, nitric oxide, is necessary for successful infection in wheat. These studies reveal potential targets for pathogen control.
Reactive oxygen species (ROS) play an important role during host–pathogen interactions and are often an indication of induced host defence responses. In this study, we demonstrate for the first time that Puccinia triticina (Pt) generates ROS, including superoxide, H2O2 and hydroxyl radicals, during wheat infection. Through pharmacological inhibition, we found that ROS are critical for both Pt urediniospore germination and pathogenic development on wheat. A comparative RNA-Seq analysis of different stages of Pt infection process revealed 291 putative Pt genes associated with the oxidation–reduction process. Thirty-seven of these genes encode known proteins. The expressions of five Pt genes, including PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod, were subsequently verified using RT-qPCR analysis. The results show that the expressions of PtNoxA, PtNoxB, PtNoxR, PtCat and PtSod are up-regulated during urediniospore germination. In comparison, the expressions of PtNoxA, PtNoxB, PtNoxR and PtCat are down-regulated during wheat infection from 12 to 120 h after inoculation (HAI), whereas the expression of PtSod is up-regulated with a peak of expression at 120 HAI. We conclude that ROS are critical for the full virulence of Pt and a coordinate down-regulation of PtNox genes may be important for successful infection in wheat.