Final Report Summary - TRADEOFF METAL (Trade-offs in immunity in the metal hyperaccumulator Noccaea caerulescens)
Marie Curie FP7-PEOPLE-2012-IEF
TRADE-OFF METAL
Publishable summary
Metal hyperaccumulating plants are able to accumulate exceptionally high concentrations of metals, such as Zinc, Nickel, and Cadmium, in their shoots to levels that would be toxic to most other plant species. The trait of metal hyperaccumulation has evolved independently multiple times in the plant kingdom. Although our understanding of the molecular mechanisms involved in metal uptake and tolerance is advancing, not much is known about the processes that have led to the evolution of metal hyperaccumulation in plants. Recent studies have provided new insight into the ecological and evolutionary significance of this trait by showing that the metal hyperaccumulating plant Noccaea caerulescens can use high concentrations of accumulated metals to defend itself against attack by pathogenic microorganisms [1]. Interestingly, infected N. caerulescens plants show few of the inducible defence responses that are used by most plants to provide protection against infection [2], which suggests that it relies on accumulated metal for disease resistance. The fact that these plants have evolved the ability to uptake and store metals in their shoot tissue, but have in turn lost defences common to most plants suggests a trade-off in expressing both traits. The present project aims to study the evolutionary, ecological and functional processes involved in the gain of metal hyperaccumulation and loss of other defensive traits in N. caerulescens.
The first step towards identifying the presence of the trade-off between hyperaccumulation and inducible defences consisted of a large-scale phenotypic evaluation of different N. caerulescens genotypes (individuals) regarding their hyperaccumulation and defence properties in the first year of the project (Objective 1). The aim thereby was to select individuals, which exhibit phenotypic signatures of the trade-off. In the following step, responsible genes were to be identified obtaining transcriptome data for the selected individuals (using RNAseq technology) in presence and absence of pathogens and/or metal treatment (Objective 2) and these candidate genes will be further analysed through evolutionary approaches during the second year of the project (Objective 3). In the last part of the project, phenotype, genotype and evolutionary history of the investigated genes will be correlated with one another to obtain a more complete picture of evolutionary as well as molecular mechanisms involved in the trade-off between metal hyperaccumulation and inducible defences (Objective 4).
The first objective of the project, the phenotyping, aimed to identify individuals, which exhibit phenotypic signatures of the trade-off, namely: efficient accumulation of metal while being hampered in the expression of costly inducible defences and vice versa. To achieve this aim, plants originating from one population of N. caerulescens were grown on low or high zinc concentrations and were then mock treated or infected with P. syringae pv. maculicola for which N. caerulescens is a suitable host [1]. Treated plants were then phenotyped regarding their ability to accumulate zinc into the leaf tissue, production of stress indicators such as reactive oxygen species (ROS), level of susceptibility to bacterial infection and level of induced defences such as production of ROS or cell death. These experiments revealed that all tested plant genotypes grown on high Zn-concentrations were more resistant to the pathogen and infection would not cause cell death in all those plants. In contrast, plants growing on low metal concentrations were more susceptible to infection and would undergo cell death from few hours after infiltration. There were differences between plants originating from the same and from different genotypes and plants from two genotypes, which exhibited the most reliably reproducible differences, were selected for further investigations.
In the following step, responsible genes were to be identified obtaining transcriptome data for the selected individuals in presence and absence of pathogens and/or metal treatment. A total of 24 plants from the two genotypes described above were selected for transcriptome analysis. RNA was extracted from these individuals and submitted to whole transcriptome sequencing using RNAseq-technology. The data have been returned recently from the sequencing facility and are currently being analysed. Genes which appear to be correlated with the phenotypic observations will be identified and these candidate genes will be further analysed through evolutionary approaches. In the last part of the project, phenotype, genotype and evolutionary history of the investigated genes will be correlated with one another to obtain a more complete picture of evolutionary as well as molecular mechanisms involved in the trade-off between metal hyperaccumulation and inducible defences.
In summary, the project will provide new insights into the evolution and ecology of metal hyperaccumulation and will thus contribute to our understanding of the impact of abiotic factors on species persistence and adaptation in particular for species occurring in fragmented and/or anthropogenic habitats such as industrial sites. In addition, it will reveal how plant responses to biotic and abiotic stress may be connected on the molecular level. The project also addresses an issue of significant practical importance because metal hyperaccumulating plants are currently being considered for biofortification and phytoremediation purposes both in the EU and worldwide.
References
1. Fones, H.N. et al., 2010, PLoS Pathog, 6(9): p. e1001093.
2. Fones, H.N. et al., 2013, New Phytol, 199(4): p. 916-24.
TRADE-OFF METAL
Publishable summary
Metal hyperaccumulating plants are able to accumulate exceptionally high concentrations of metals, such as Zinc, Nickel, and Cadmium, in their shoots to levels that would be toxic to most other plant species. The trait of metal hyperaccumulation has evolved independently multiple times in the plant kingdom. Although our understanding of the molecular mechanisms involved in metal uptake and tolerance is advancing, not much is known about the processes that have led to the evolution of metal hyperaccumulation in plants. Recent studies have provided new insight into the ecological and evolutionary significance of this trait by showing that the metal hyperaccumulating plant Noccaea caerulescens can use high concentrations of accumulated metals to defend itself against attack by pathogenic microorganisms [1]. Interestingly, infected N. caerulescens plants show few of the inducible defence responses that are used by most plants to provide protection against infection [2], which suggests that it relies on accumulated metal for disease resistance. The fact that these plants have evolved the ability to uptake and store metals in their shoot tissue, but have in turn lost defences common to most plants suggests a trade-off in expressing both traits. The present project aims to study the evolutionary, ecological and functional processes involved in the gain of metal hyperaccumulation and loss of other defensive traits in N. caerulescens.
The first step towards identifying the presence of the trade-off between hyperaccumulation and inducible defences consisted of a large-scale phenotypic evaluation of different N. caerulescens genotypes (individuals) regarding their hyperaccumulation and defence properties in the first year of the project (Objective 1). The aim thereby was to select individuals, which exhibit phenotypic signatures of the trade-off. In the following step, responsible genes were to be identified obtaining transcriptome data for the selected individuals (using RNAseq technology) in presence and absence of pathogens and/or metal treatment (Objective 2) and these candidate genes will be further analysed through evolutionary approaches during the second year of the project (Objective 3). In the last part of the project, phenotype, genotype and evolutionary history of the investigated genes will be correlated with one another to obtain a more complete picture of evolutionary as well as molecular mechanisms involved in the trade-off between metal hyperaccumulation and inducible defences (Objective 4).
The first objective of the project, the phenotyping, aimed to identify individuals, which exhibit phenotypic signatures of the trade-off, namely: efficient accumulation of metal while being hampered in the expression of costly inducible defences and vice versa. To achieve this aim, plants originating from one population of N. caerulescens were grown on low or high zinc concentrations and were then mock treated or infected with P. syringae pv. maculicola for which N. caerulescens is a suitable host [1]. Treated plants were then phenotyped regarding their ability to accumulate zinc into the leaf tissue, production of stress indicators such as reactive oxygen species (ROS), level of susceptibility to bacterial infection and level of induced defences such as production of ROS or cell death. These experiments revealed that all tested plant genotypes grown on high Zn-concentrations were more resistant to the pathogen and infection would not cause cell death in all those plants. In contrast, plants growing on low metal concentrations were more susceptible to infection and would undergo cell death from few hours after infiltration. There were differences between plants originating from the same and from different genotypes and plants from two genotypes, which exhibited the most reliably reproducible differences, were selected for further investigations.
In the following step, responsible genes were to be identified obtaining transcriptome data for the selected individuals in presence and absence of pathogens and/or metal treatment. A total of 24 plants from the two genotypes described above were selected for transcriptome analysis. RNA was extracted from these individuals and submitted to whole transcriptome sequencing using RNAseq-technology. The data have been returned recently from the sequencing facility and are currently being analysed. Genes which appear to be correlated with the phenotypic observations will be identified and these candidate genes will be further analysed through evolutionary approaches. In the last part of the project, phenotype, genotype and evolutionary history of the investigated genes will be correlated with one another to obtain a more complete picture of evolutionary as well as molecular mechanisms involved in the trade-off between metal hyperaccumulation and inducible defences.
In summary, the project will provide new insights into the evolution and ecology of metal hyperaccumulation and will thus contribute to our understanding of the impact of abiotic factors on species persistence and adaptation in particular for species occurring in fragmented and/or anthropogenic habitats such as industrial sites. In addition, it will reveal how plant responses to biotic and abiotic stress may be connected on the molecular level. The project also addresses an issue of significant practical importance because metal hyperaccumulating plants are currently being considered for biofortification and phytoremediation purposes both in the EU and worldwide.
References
1. Fones, H.N. et al., 2010, PLoS Pathog, 6(9): p. e1001093.
2. Fones, H.N. et al., 2013, New Phytol, 199(4): p. 916-24.