Abstract
Heavy metals such as cadmium (Cd) and mercury (Hg) pose significant threats to plant health and food safety as they are absorbed from the environment. Legumes are generally considered sensitive to heavy metals but possess standing genetic variation for accumulation and tolerance to toxic ions. We conducted a transcriptomic analysis on hydroponically and soil grown Medicago truncatula plants to investigate gene expression responses to Cd and Hg exposure in roots, leaves, and nodules. By using plant genotypes with varying metal tolerance or accumulation levels, we observed distinct clustering of gene ontologies, indicating tissue-specific, genotype-specific, and metal-specific gene expression patterns. Considering the symbiotic relationship between legumes and nitrogen-fixing bacteria, we further examined plant phenotypes and transcriptomes of plant genotypes with contrasting Hg accumulation levels and inoculated them with high or low Hg-tolerant Sinorhizobium medicae strains that have presence-absence variation for a mercury reductase (Mer) operon. Host plants inoculated with the Hg-tolerant rhizobia strain possessing a Mer operon exhibited less reduction in nodule number and plant biomass. A smaller reduction in iron (Fe) distribution in nodules after Hg stress was measured using X-ray Fluorescence (XRF) imaging. Dual transcriptome (host plant and bacteria) analysis of nodules revealed a remarkable decrease in the number of differentially expressed genes (DEGs) and clustering of gene ontologies in plants inoculated with the Hg-tolerant rhizobia strain, including symbiosis related genes. This finding suggests that the Hg-tolerant rhizobia strain has the potential to mitigate Hg stress in host plants. Furthermore, we observed genotype by-genotype interactions between the high Hg accumulating plant genotype and the Hg-tolerant rhizobia strain. These findings provide insights into enhancing plant resilience in contaminated environments through optimizing legume-rhizobia interactions for heavy metal tolerance.
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Claims 7
Claim · model-written summary
Gene ontology clusters indicated tissue-specific expression patterns.
- Taxon
- Medicago truncatula
Medicago truncatulat0 - Outcome
- tissue-specific, genotype-specific, and metal-specific gene expression patternse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we observed distinct clustering of gene ontologies, indicating tissue-specific, genotype-specific, and metal-specific gene expression patterns”
t0“Medicago truncatula”
Claim · model-written summary
The Hg-tolerant rhizobial strain with a Mer operon reduced the loss of nodule number.
- Taxon
- Medicago truncatulaMedicago truncatulat0
- Treatment
- inoculated with the Hg-tolerant rhizobia strain possessing a Mer operone0
- Interactor
- rhizobia straine0symbiont
- Gene
- Mer operone0
- Outcome
- nodule numbere0
- Direction
- less reductione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Host plants inoculated with the Hg-tolerant rhizobia strain possessing a Mer operon exhibited less reduction in nodule number and plant biomass”
t0“Medicago truncatula”
Claim · model-written summary
The Hg-tolerant rhizobial strain with a Mer operon reduced the loss of plant biomass.
- Taxon
- Medicago truncatulaMedicago truncatulat0
- Treatment
- inoculated with the Hg-tolerant rhizobia strain possessing a Mer operone0
- Interactor
- rhizobia straine0symbiont
- Gene
- Mer operone0
- Outcome
- plant biomasse0
- Direction
- less reductione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Host plants inoculated with the Hg-tolerant rhizobia strain possessing a Mer operon exhibited less reduction in nodule number and plant biomass”
t0“Medicago truncatula”
Claim · model-written summary
Nodule iron distribution declined less after Hg stress.
- Taxon
- Medicago truncatulaMedicago truncatulat0
- Treatment
- Hg stresse0
- Outcome
- iron (Fe) distribution in nodulese0
- Direction
- smaller reductione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A smaller reduction in iron (Fe) distribution in nodules after Hg stress was measured using X-ray Fluorescence (XRF) imaging”
t0“Medicago truncatula”
Claim · model-written summary
The Hg-tolerant rhizobial strain decreased plant differentially expressed gene counts.
- Taxon
- Medicago truncatulaMedicago truncatulat0
- Treatment
- inoculated with the Hg-tolerant rhizobia straine0
- Interactor
- rhizobia straine0symbiont
- Outcome
- number of differentially expressed genes (DEGs)e0
- Direction
- decreasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a remarkable decrease in the number of differentially expressed genes (DEGs) and clustering of gene ontologies in plants inoculated with the Hg-tolerant rhizobia strain, including symbiosis related genes”
t0“Medicago truncatula”
Claim · model-written summary
Gene ontology clustering changed with Hg-tolerant rhizobial inoculation.
- Taxon
- Medicago truncatulaMedicago truncatulat0
- Treatment
- inoculated with the Hg-tolerant rhizobia straine0
- Interactor
- rhizobia straine0symbiont
- Outcome
- clustering of gene ontologiese0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“clustering of gene ontologies in plants inoculated with the Hg-tolerant rhizobia strain, including symbiosis related genes”
t0“Medicago truncatula”
Claim · model-written summary
The high Hg-accumulating plant genotype interacted with the Hg-tolerant rhizobial strain.
- Taxon
- Medicago truncatulaMedicago truncatulat0
- Material
- high Hg accumulating plant genotypee0
- Interactor
- rhizobia straine0symbiont
- Outcome
- genotype by-genotype interactionse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we observed genotype by-genotype interactions between the high Hg accumulating plant genotype and the Hg-tolerant rhizobia strain”
t0“Medicago truncatula”
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