Trade-offs between elemental defences and innate immunity in the metal hyperaccumulator plant Noccaea caerulescens

Metal hyperaccumulation is an unusual trait that has been observed in around 400 plant species [1]. Our work using the model metal hyperaccumulator plant Noccaea caerulescens has provided strong support for the hypothesis that metal accumulation provides defence against plant pathogens through the toxicity of accumulated metal to microorganisms, a hypothesis sometimes referred to as the “elemental defence” hypothesis [2-5]. We have also shown that N. caerulescens lacks certain features of the plant immune system that are present in the majority of non-metal hyperaccumulating plants [3,4,6,7]. This suggests that metal hyperaccumulation is physiologically incompatible with some plant immune responses, or confers a high fitness cost, resulting in a trade-off between metal hyperaccumulation and other plant defence mechanisms. 

In this project we will investigate the hypothesis that trade-offs between metal hyperaccumulation and immunity have led to the loss of defence responses in N. caerulescens, but that N. caerulescens retains a core immune response that continues to provide protection against infection. We will ask: (1) Which defence pathways have been inactivated or suppressed due to a trade off with metal hyperaccumulation; and (2) Which defences act to limit pathogen infection? 

Background: Metal hyperaccumulation is an unusual trait that has been observed in around 400 plant species [1]. Our work using the model metal hyperaccumulator plant Noccaea caerulescens has provided strong support for the hypothesis that metal accumulation provides defence against plant pathogens through the toxicity of accumulated metal to microorganisms, a hypothesis sometimes referred to as the “elemental defence” hypothesis [2-5]. We have also shown that N. caerulescens lacks certain features of the plant immune system that are present in the majority of non-metal hyperaccumulating plants [3,4,6,7]. This suggests that metal hyperaccumulation is physiologically incompatible with some plant immune responses, or confers a high fitness cost, resulting in a trade-off between metal hyperaccumulation and other plant defence mechanisms. 

Aim and Rationale: In this project we will investigate the hypothesis that trade-offs between metal hyperaccumulation and immunity have led to the loss of defence responses in N. caerulescens, but that N. caerulescens retains a core immune response that continues to provide protection against infection. We will ask: (1) Which defence pathways have been inactivated or suppressed due to a trade off with metal hyperaccumulation; and (2) Which defences act to limit pathogen infection? 

Interestingly, we have observed a considerable degree of variability between N. caerulescens populations both in metal hyperaccumulation and in their response to pathogen infection and the environment [7]. Thus, an extended goal of this project will be to explore the evolution and ecology of metal hyperaccumulation and disease resistance in natural populations of N. caerulescens in the UK and Europe. A deeper understanding of the biology and evolution of these fascinating plants will provide important new insights into plant adaptations to their environment and to environmental change.  

There is considerable flexibility within this research topic to adapt the questions, methods and supervisory team to the expertise and interests of individual researchers, and I encourage students to get in contact to discuss possible research directions.  

Microbiological techniques, plant cultivation and hydroponics, molecular biology techniques, transcriptomics, bioinformatics, proteomics, biochemical analyses, microscopy and imaging techniques (potentially including X-ray fluorescence and XANES in collaboration with Diamond Light Source). 

All necessary skills can be acquired in the course of study. This project would suit a student who wishes to explore questions in plant ecology, plant pathology and evolution while gaining experience in molecular methods and in biochemical and/or imaging techniques.