An RNA cascade and disease resistance in tomato

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Growth, development and responses to the environment of all organisms - life - depends on regulated activity of genes. If this regulation does not occur the consequence is death or disease but, in some examples, if it is perturbed there is evolutionary advance. In crops and agriculture, for example, there are many examples of important traits due to mutation of regulatory pathways that have persisted because farmers selected the seed from these mutant plants. More recently plant breeders have carried out the selection. In this project we will illustrate a modern variation on this process in which we will engineer mutant plants with enhanced disease resistance. In the historical situations the mutants arose randomly and they would have been selected because they performed better or gave higher quality produce than the non-mutant progenitor. In this project the difference from the historical plant breeding is that the mutations will be targeted by an emerging technology known as gene editing. These mutations will be introduced at genetic regulatory sites in the genome that normally reduce the activity of disease resistance pathways in the plant. The consequence of the mutation will, therefore, be enhanced disease resistance. The experimental approach is based on preliminary experiments in which we disrupted a regulatory cascade affecting the innate immune system of tomato. The nodes in this cascade are the mRNAs encoding defense proteins and the connecting edges are small regulatory RNAs known as miRNAs. At present we do not know the full extent of this cascade or whether the different branches have overlapping or non-overlapping functions but we know that when the cascade system is blocked the plants exhibit enhanced resistance against late blight caused by a filamentous pathogen responsible for the potato famine in Ireland in the 1840s. This pathogen is often a problem for tomato growers. The plants were also partially resistant against a bacterium and, because these are such different pathogens, we infer that disrupting this miRNA cascade may confer resistance against a broad spectrum of other pathogens.In the proposed work we aim to understand the miRNA cascade regulation of disease resistance in more detail. In getting this information, we will learn more about the ways that miRNAs act and so the information from this project will have more general relevance to understanding of genetic regulation. The project will test the spectrum of pest and pathogen resistance that can be achieved through the disruption the miRNA cascade and we will have set up later translational work that will use gene edited plants with enhanced disease resistance as part of a new approach to sustainable agriculture. The experiments will all be carried out in tomato but the miRNA cascade regulation of disease resistance features in many plants and so our findings will be more generally relevant to a wide range of crops.