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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Hyperaccumulator | 2/2 | https://en.wikipedia.org/wiki/Hyperaccumulator | reference | science, encyclopedia | 2026-05-05T07:18:38.913323+00:00 | kb-cron |
=== Genetic basis of hyperaccumulation === An overexpression of a Zn transporter gene, ZNT1, in root and shoot tissue is an essential component of the Zn hyperaccumulation trait in T. caerulescens. This increased gene expression has been shown to be the basis for increased Zn2+ uptake from the soil in T. caerulescens roots, and it is possible that the same process underpins the enhanced Zn2+ uptake into leaf cells.The proteins are coded by genes in the ZIP family, however other families such as the HMA (heavy metal ATPase), MATE, YSL and MTP families have also been observed to be involved. The ZIP gene family encodes Cd, Mn, Fe and Zn transporters. The ZIP family plays a role in supplying Zn to metalloproteins. In one study on Arabidopsis, it was found that the metallophyte Arabidopsis halleri expressed a member of the ZIP family that was not expressed in a non-metallophyte sister species. This gene was an iron-regulated transporter (IRT-protein) that encoded several primary transporters involved with cellular uptake of cations above the concentration gradient. When this gene was transformed into yeast, hyperaccumulation was observed. This suggests that overexpression of ZIP family genes that encode cation transporters is a characteristic genetic feature of hyperaccumulation. Another gene family that has been observed ubiquitously in hyperaccumulators are the ZTP and ZNT families. A study on T. caerulescens identified the ZTP family as a plant specific family with high sequence similarity to other zinc transporter. Both the ZTP and ZNT families, like the ZIP family, are zinc transporters. It has been observed in hyperaccumulating species, that these genes, specifically ZNT1 and ZNT2 alleles are chronically overexpressed. AhHMHA3 is expressed in hyperaccumulating individuals. AhHMHA3 has been identified to be expressed in response to and aid of Zn detoxification. In another study, using metallophytic and non-metallophytic Arabidopsis populations, back crosses indicated pleiotropy between Cd and Zn tolerances. This response suggests that plants are unable to detect specific metals, and that hyperaccumulation is likely a result of an overexpressed Zn transportation system. One of the most well-documented HMAs is HMA4, which belongs to the Zn/Co/Cd/Pb HMA subclass and is localized at xylem parenchyma plasma membranes. HMA4 is upregulated when plants are exposed to high levels of Cd and Zn, but it is downregulated in its non-hyperaccumulating relatives. Also, when the expression of HMA4 is increased there is a correlated increase in the expression of genes belonging to the ZIP (Zinc regulated transporter Iron regulated transporter Proteins) family.
=== Genetic Engineering of Hyperaccumulators === Genetic engineering has been used to research potential improvements towards hyperaccumulation efficiency and species resistance to biological side effects of metal uptake. Methods have included engineering overexpression of pollutant degrading enzymes or proteins associated with heavy metal transportation pathways, and transgenesis, where genes from hyperaccumulators are inserted into the genome of other hyperaccumulators to target specific metals or metals previously inaccessible to that species. For example, Sedum plumbizinicicola is a hyperaccumulator of Cd using the heavy metal transporter genes SpHMA2, SpHMA3, and SpNramp6. In 2023, Yang et al. inserted these genes into Brassica napus, or Rapeseed plants, resulting in high uptake efficiency and sequestration of Cd compared to the wild-type rapeseed. Transgenic phytoextractors theoretically function to combine favorable traits like high biomass production with hyperaccumulation, showing the potential to improve the speed of phytoremediation. However, research reports often do not include long term data of artificial phytoextraction by transgenic plants to see if they can actually survive their entire life cycle intaking hyperaccumulator-levels of contaminants. Site implementation of transgenic plants for phytoremediation is also controversial, due to how these plants could negatively impact native biodiversity.
=== Molecular pathway === Often hyperaccumulation is the result of promiscuous zinc binding, i.e. protein-based sequestrants, transporters, etc with a high affinity for zinc that will bind other metal ions. Metals ions in solution are susceptible to extraction. For example, ligands secreted by plant - phytosiderophores, organic acids, or carboxylates -can selectively binds certain ions.
== Metal Excluders == A metal excluder is a category of metallophyte that absorbs metals at only their roots.
== Metal Indicators == A metal indicator is a metallophyte that accumulates heavy metal concentration in shoots and leaves.While good at absorbing metals, they eventually succumb to the metals' toxicity.
== Other Examples == Alpine pennycress (Thlaspi caerulescens), the zinc violet (Viola calaminaria), spring sandwort (Minuartia verna), sea thrift (Armeria maritima), Cochlearia, common bent (Agrostis capillaris), and plantain (Plantago lanceolata).
== Further reading == K.B. Axelsen and M.G. Palmgren, Inventory of the superfamily of P-Type ion pumps in Arabidopsis. Plant Physiol., 126 (1998), pp. 696–706.
== See also == Biohydrometallurgy Calaminarian grassland Chara baltica Cladophora socialis Coccotylus Furcellaria Polysiphonia Stuckenia pectinata Zannichellia palustris List of hyperaccumulators Phytoremediation
== References ==
- Souri Z, Karimi N, Luisa M. Sandalio. 2017. Arsenic Hyperaccumulation Strategies: An Overview. Frontiers in Cell and Developmental Biology. 5, 67. DOI: 10.3389/fcell.2017.00067.