Improving plants’ resistance to pests
Over 75 years ago Harold Henry Flor revealed that inheritance of plant resistance and parasitism is determined by matching single genes in plants and pathogens. Since then numerous studies have shown that the functional principles of plant resistant gene-mediated immunity is far more complex than the simple binary view proposed by Flor. The current paradigm is that plant disease resistance is encoded by dynamic repertoires of immune receptors interconnected in genetic and biochemical networks. Identification of pathogen effectors The Marie Skłodowska-Curie fellow, Dr Lida Derevnina, worked in the laboratory of Prof. Sophien Kamoun at the Sainsbury Laboratory, Norwich, United Kingdom. Under the EU-funded project BoostR, they expanded existing knowledge on an intracellular immune receptor network that is composed of nucleotide-binding domain leucine-rich repeat (NLR) proteins. Members of the NLR network are evolutionarily related and likely expanded over 100 million years ago, conferring resistance to diverse pathogens of the Solanaceae family. Known as the nightshades, the Solanaceae include many agriculturally important crops including tomatoes, potatoes and tobacco. Within the network, three helper NLRs, known as NRCs, initiate the defence signal, and are required by a group of agronomically important sensor NLRs that are specialised to recognise pathogen molecules. NRC helpers play an instrumental role, functioning in both a redundant and non-redundant manner to allow sensor-mediated immune responses. BoostR scientists worked under the hypothesis that altering NRCs will improve disease resistance in Solanaceae crops against a number of devastating pathogens. “My proposal aims to generate synthetic NRCs that possess broad-spectrum disease resistance,″ explains Dr Derevnina. She conducted all experiments using the model plant organism, Nicotiana benthamiana, a Solanaceous plant species, and screened effectors from diverse pathogens for their ability to suppress NRC signalling. The scientist identified two such effectors – AVRcap1b from P. infestans and SPRYSEC from Globodera spp – and described their mode of action. Using this information, it was possible to produce chimeric NRCs by swapping protein domains in different combinations to identify candidates that maintained upstream signalling with NRC dependent sensor NLRs, but evaded suppression by pathogen effectors. Following validation, through gene complementation assays, these chimeras were tested in proof-of-concept experiments, and will be tested in tomato and potato to determine their value in breeding programmes. Impact of engineering the plant immune system As Dr Derevnina emphasises “the fact that these pathogens are evolutionarily divergent but converged to target the same host pathway, highlights the importance NRC helper proteins play in mediating immunity against various Solanaceae infecting pathogens.″ Studying pathogen effectors that target NRC proteins, both directly and indirectly, allows us to improve our understanding of the molecular mechanisms underlying both pathogen infection and host recognition, and helps improve our understanding of NLR function. Most importantly, it offers us new strategies for breeding plants with enhanced resistance. The outcome of the project has far-reaching implications in agriculture, opening the possibility of cultivating crops resistant to a diversity of agronomically important pathogens, thereby, increasing yield and minimising the use of pesticides. Dr Derevnina envisages “the new field of studying plant immune receptor networks to play a paramount role from now on in disease resistance breeding programmes worldwide.″
Keywords
BoostR, pathogen, resistance, NRC, NLR, immune system, pesticide, chimeric NRC
