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Harnessing the immune defences of plants for better crop yields

Like animals, plants have an immune system and like animals, it can fail, resulting in disease and leading to agriculture yield loss. A better understanding of how and why the plant immune system functions can help pest management systems work in harmony with the environment.

Food and Natural Resources

Crop loss to pests and disease is a major challenge for agriculture worldwide, recently estimated to cause up to a 40 % loss in yield potential. Attempts to control pathogens with chemical sprays can have detrimental ecosystem effects, and pathogens frequently develop resistance. Plants can protect themselves in many cases, activating a first layer of immunity called pathogen-triggered immunity (PTI) when detecting microbes. This ‘high alert’ mode renders them more resistant to infection, partly through changing the expression of thousands of genes. transcriPTIon studied this response in the model plant Arabidopsis thaliana, using a wide variety of microbe-derived molecules. The EU-supported project found that early gene expression patterns were remarkably similar when responding to different pathogens. Many patterns were even conserved for plant responses to very different stresses. RNA sequencing using an unprecedented diversity of pathogens Plants detect pathogens through membrane-bound receptors at the surface of cells, which recognise microbial signatures, so-called elicitors. Plants respond by enabling PTI, through a massive transcriptional reprogramming of which genes are expressed/not expressed. “We know a lot about how plants detect microbes, but less about how they actually protect themselves. Prior to the project, we didn’t really know how tailored the response would be, or how quickly it would take effect,” MSCA Fellow Dr Marta Bjornson says. transcriPTIon studied defined signalling components in the model plant Arabidopsis thaliana. “Investigation within a controlled system makes getting to the core regulatory principles, potentially conserved among all plant-microbe interactions, easier,” says Dr Bjornson. To probe the transcriptional logic of plant immunity, transcriPTIon took a set of seven different elicitors, and treated plants with each. A plant RNA sample was then taken at six points, from 5 minutes to 3 hours afterwards. This revealed patterns in gene expression across all elicitors and all time points and transcription factors which might regulate these patterns. transcriPTIon found that all elicitors induced a large core set of genes, especially in the first minutes after elicitor detection, and these genes were also induced in the plant’s early response to many abiotic stresses such as salt, extreme temperatures and strong light. This suggests that the initial response is not specifically an immune response, but rather a general stress response. Later responses became more specific: one elicitor induced many genes uniquely. Even at later time points though, a small core gene set was induced by all elicitors and by no abiotic stresses, suggesting a specialised PTI response. Food security and sustainable agriculture transcriPTIon has defined the extent and timing of the common PTI and abiotic-stress responses. Applications based on transcriPTIon’s results could enhance the innate immunity of crop plants, increasing yield stability and decreasing reliance on pesticides. “Work remains for any marketable product. We are still looking at candidate genes affecting resistance to a model pathogen in a model plant – anything we find would need to be tested in crop plants, various pathogens and field conditions,” Dr Bjornson says. Dr Bjornson is currently testing transcription factors implicated by transcriPTIon and has already found that at least one regulator of the general stress response is necessary for PTI. She is also investigating a number of genes that seem to be regulated specifically in response to pathogens, but not other stresses.

Keywords

transcriPTIon, disease, plant, infection, immune system, microbial, pathogen, crops, food security, pest management, resistance

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