Roles Of Alternative Oxidase In The Interaction Between Plants And Pathogens

Plants and fungi possess two mitochondrial respiration pathways. One is cyto-chrome pathway with cytochrome oxidase as the terminal oxidase. Another one is alternative pathway with alternative oxidase as the terminal oxidase. Alternative pathway branches from cytochrome pathway at the point of ubiquinone, alternative oxidase is cyanide-resistant, but sensitive to substituted hydroxamic acids, such as salicylhydroxamic acid. It transfers electrons from reduced ubiquinone to oxygen without ATP formation, which seems to cause energy waste. However, research with plants has confirmed that alternative oxidase respiration is of particular importance during abiotic and biotic stress. Furthermore, alternative oxidase has even been pro-posed to act to provide a signaling homeostasis from the mitochondrion that controls cellular responses of plants to stress.Sclerotinia sclerotiorum is a filamentous fungal pathogen that can infect many kinds of crops. It’s the causal agent of rape sclerotinia rot, a disease of oilseed rape that can cause devastating losses of both yield and quality. As in plants, alternative oxidase can also play roles in resistance of fungi to oxidative stress. One more func-tion of fungal alternative oxidase is that it has been reported to be involved in the sensitivity regulation of fungi to some fungicides, especially with the Quinol oxida-tion-inhibiting fungicides. Application of fungicides is the major approach to con-trol the diseases caused by this pathogen though the high level of resistance present in this fungi. This may provide an evidence to develop new inhibitor to control the fungi as considered the alternative respiration as a viable target.In this paper three parts have been referred to:influences of3-AT in the infec-tion of tobacco mosaic virus to tobacco with genetically modified alternative oxidase gene; involvement of alternative oxidase in the regulation of growth, development, and resistance to oxidative stress of Sclerotinia sclerotiorum; involvement of alterna-tive oxidase in the regulation of sensitivity of Sclerotinia sclerotiorum to various fungicides. The main results are as follows:1. Transgenic tobacco plants with modified alternative oxidase gene expression levels has the same cytochrome pathway, although they exhibited different alterna-tive pathway, the results show that modification of the alternative payhway capacity of tobacco plants does not affect their basal resistance or susceptibility to tobacco mosaic virus.2. Transgenic plants with altered alternative respiratory capacity display normal tobacco mosaic virus-induced systemic disease development on inoculated leaves with exogenous hydrogen peroxide, but pre-treatment with the inhibitor of catalase, a transgenic line with increased alternative pathway became more sensitive to the to-bacco mosic virus.3. A transgenic line with increased alternative pathway was more sensitive to the resistance induced by higher level of reduced glutathione, but the induction was an-tagonized by the pre-treatment with the inhibitor of catalase.4. Exogenous hydrogen peroxide had no impact on the alternative oxidase level, but the inhibitor of catalase was an effective inducer to induce alternative oxidase on the transgenic line with decreased alternative pathway and normal alternative path-way.5. Alternative oxidase accelerated Sclerotinia sclerotiorum forming sclerotia and mycelia growth rate while hydrogen peroxide in millimolar concentrations greatly decreased the growth rate of mycelia and delayed the formation of sclerotia. As well, this treatment obviously increased their alternative pathway respiration and the lev-els of mRNA of alternative oxidase. These results indicate that alternative oxidase is involved in the regulation of growth, development, and resistance to oxidative stress of Sclerotinia sclerotiorum.6. Alternative oxidase decreased sensitivity to the azoxystrobin while increased sensitivity to the other five fungicides. The result indicated that alternative oxidase was involved in the sensitivity regulation of Sclerotinia sclerotiorum to the six tested fungicides, most of which could affect its alternative oxidase gene transcription and the alternative respiration pathway capacity development in turn.In summary, this research shows that the mitochondrial alternative oxidase was involved in plant and pathogen interaction. It also regulates fungal growth, develop- ment, stress of oxidation resistance and the sensitivity of the fungicide. Researches on the detached leaves and Sclerotinia sclerotiorum of alternative oxidase were rare, based on this model, it provides a theoretical basis on the plant resistance and reduc-ing the pathogenicity of pathogens.