The modulation of plant isoprenoids as a strategy for ozone tolerance

   School of Biological Sciences

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  Prof P Fraser, Dr G Enfissi, Dr Laura Perez , Prof Martin King  No more applications being accepted  Competition Funded PhD Project (UK Students Only)

About the Project

The combustion of fossil fuels, and biomass has led to elevated ambient ozone concentrations over large portions of the earth’s surface. Increased levels of ozone result in cellular damage to vegetative tissues, adversely affecting photosynthesis and plant growth (Ashmore, 2016. PCE., 28, 949). Economically crop losses due to ozone direct are in the range of several billion dollars annually and rising. 

Isoprenoids or terpenoids are chemicals produced by plants/crop that have been associated with the dissipation of environmental ozone and its effects. Among the classes of isoprenoids that exist, the diterpenoids and triterpenoids with both exo and endo cyclic double bonds have been shown to react with ozone and in some cases provide an efficient ozone sink; while improving the ozone tolerance of plants/crops (Jud et al., 2016. Atmos. Chem. Phys, 16, 277). The reaction process between environmental ozone and the natural plant products is termed ozonolysis (Criegee, 1975. Angew. Chem. Int. Ed. Engl. 14, 745).   

Our aim is to demonstrate the potential of plants/crops with altered isoprenoid contents to act as efficient sinks capable of modulating atmospheric ozone, while concurrently providing plant/crop with tolerance to ozone. For the proposed study Nicotaina tabacum (tobacco) will be used. This is because the applicants through EU-H2020 funding have developed and chemotyped a panel of natural diversity, that cover all the present known biodiversity in this genus (Drapal et al., 2022. The Plant Journal, 110, 1516). Within this core collection there are a wide range of isoprenoid contents and also trichome structures. These trichome structures are specialised plant tissues that contain glands containing natural oils, in many cases wide ranging isoprenoids are present within these structures. In addition, the structures are found on the surface of leaves with direct environmental contact and participate in gaseous exchange.

Besides the utilisation of biodiversity, the applicants have created genetic resources in which isoprenoid levels have been modulated by metabolic engineering. Squalene is an example of a triterpenoid that readily reacts with ozone. Through ortholog intragenic engineering industrial tobacco genotypes have been generated that produce high (10mg/gDW) levels of squalene in both the glasshouse and industrial relevant field trials. The potential of these genotypes to confer tolerance to ozone will be assessed. Tobacco is both a model and crop plant and being a Solanaceae species, the technologies can readily be transferred to other Solanaceae food crops such as tomato and Capsicum. Using the unique germplasm available there are several key hypotheses driven questions that can be addressed; (i) can natural variation (biodiversity) be exploited to capture genetic tools and resources for the development of crops tolerant to atmospheric ozone? (ii) what is the chemistry underlying the interaction of ozone with terpenoids? and (iii) does the potential exist to engineer biology to create ozone tolerant crops?

Experimentally, the project will address these questions by culturing the material in different atmospheres of increasing ozone content, which will be administered over dedicated treatment periods. The effects of ozone treatment on metabolism will be revealed by metabolomics, ascertaining sectors of metabolism effected. Physiological parameters including photosynthesis capacity will be recorded as will yield/biomass. Isoprenoids, their derivatives and break down products present in intact tissues, on the leaf surface, cuticle and epidermis will be measured using SPME-GC/MS and LC-MS/MS. Opportunities also exist to interact with and generate more proof of concept transgenic or edited plants with the potential to be tolerant to ozone. 

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