A functional analysis of mitochondrial respiratory chain cytochromebc1complex inGaeumannomyces triticiby RNA silencing as a possible target of carabrone

Gaeumannomyces tritici, an ascomycete soilborne fungus, causes a devastating root disease in wheat. Carabrone, a botanical bicyclic sesquiterpenic lactone, is a promising fungicidal agent that can effectively controlG. tritici. However, the mechanism of action of carabrone againstG. triticiremains largely unclear. Here, we used immunogold for subcellular localization of carabrone and the results showed that carabrone is subcellularly localized in the mitochondria ofG. tritici. We then explored the functional analysis of genesGtCytc(1),GtCytb, andGtIspof the mitochondrial respiratory chain cytochromebc(1)complex inG. triticiby RNA silencing as a possible target of carabrone. The results showed that the silenced mutant increment GtIsp is less sensitive to carabrone compared to increment GtCytc(1)and increment GtCytb. Compared with the control, the activities of complex III in all the strains, except increment GtIsp and carabrone-resistant isolate 24-HN-1, were significantly decreased following treatment with carabrone at EC(20)and EC(80)in vitro (40%-50% and 70%-80%, respectively). The activities of mitochondrial respiratory chain complex III and the mitochondrial respiration oxygen consumption rates in all the strains, except increment GtIsp and 24-HN-1, were higher with respect to the control when treated with carabrone at EC(20)in vivo. The rates of mitochondrial respiration of all strains, except increment GtIsp, were significantly inhibited following treatment with carabrone at EC80(ranging from 57% to 81%). This study reveals that the targeting of the iron-sulphur protein encoded byGtIspis highly sensitive to carabrone and provides a direction for the research of carabrone's target.