Marques et al. 2025 — Phytochelatins and cadmium mitigation via plant genetic manipulation

Marques, Thiengo, and Azevedo (Department of Genetics and Luiz de Queiroz College of Agriculture, ESALQ/USP, Piracicaba, Brazil) review the published evidence on genetic-manipulation strategies that exploit the phytochelatin (PC) pathway to modulate cadmium (Cd) tolerance, accumulation, and translocation in plants. The piece is a “Perspective” article in International Journal of Molecular Sciences combining a narrative synthesis of ~80 functional-genetics studies (Table 1) with a Web of Science bibliometric analysis of two subsets — mutant-focused (final n=39) and transgenic-focused (final n=44) — and a forward look at multigene precision-engineering and grafting strategies for phytoremediation and food-safety outcomes in Cd-contaminated agricultural systems. The review reports no primary contamination measurements in any food matrix; its value to the wiki is conceptual background for cadmium and for the mitigation/remediation-evidence section of the wiki when those pages discuss the biological mechanisms by which plants chelate, sequester, and translocate Cd.

Why this matters

• It is the most current peer-reviewed synthesis of the phytochelatin-synthase (PCS) genetic-manipulation literature for Cd mitigation, covering ~80 studies spanning Arabidopsis thaliana, Nicotiana tabacum, Oryza sativa (rice), Brassica juncea, Marchantia polymorpha, Triticum aestivum (wheat), and several non-model species across mutant, RNAi/VIGS-silencing, transgenic-overexpression, complementation, and synthetic-peptide (EC, PCL, pph6his) strategies.
• It catalogues the abbreviation and locus vocabulary the PCS-Cd literature uses (CAD1, AtPCS1, AtPCS2, OsPCS1/OsPCS2/OsPCS5/OsPCS15, TaPCS1, MpPCS, ZmPCS1, NtPCS1, etc., plus the cad1-1…cad1-6 allelic series, the ABC-transporter AtABCC1/AtABCC2/AtABCC3, HMA2/HMA4, and the GSH precursor pathway), which the wiki’s mitigation pages will need as a reading aid when they touch the underlying primary literature.
• It documents that PCS overexpression does not consistently improve Cd tolerance or accumulation — outcomes are bidirectional (tolerance, hypersensitivity, no effect) and depend on isoform, promoter strength, subcellular targeting (cytosolic vs chloroplastic vs vacuolar), GSH availability, and downstream vacuolar-transport capacity. The wiki’s framing of “more PCS = safer crop” deserves this hedge.
• It frames future directions toward multigene precision engineering combining PCS isoforms with vacuolar-sequestration genes (e.g., YCF1, AtABCC1/2/3) and long-distance metal transporters (HMA2/HMA4) under tissue-specific or stress-inducible promoters, and proposes grafting as a methodological innovation to dissect root-vs-shoot contributions to Cd accumulation. These are remediation-and-food-safety strategies relevant to the mitigation-evidence chapter, not threshold-setting inputs.

Key concepts and structure

The article has four top-level sections plus references and supplementary material. Section 1 frames cadmium and phytochelatins as strategic targets. Section 2 (“Advances in Phytochelatin Synthase Research and Plant Genetic Manipulation”) contains Table 1, which summarises the ~80 studies the synthesis is built on. Section 3 (“Research Avenues and Approaches in PC-Related Genetic Manipulation”) presents the bibliometric analysis and Figures 1–4. Section 4 (“Concluding Remarks and Additional Future Directions”) closes with the multigene-engineering and grafting recommendations. Supplementary Material S1 contains the bibliometric tables S1–S10 and is hosted at the MDPI article URL.

The biological framing the review opens with

The opening section establishes that cadmium is “highly toxic” to plants and other living organisms, persistent under various agricultural conditions, and recognised as a particularly strong inducer of PC synthase (PCS) activity. PCs are defined as cysteine-rich peptides synthesised by PCS from the precursor glutathione (GSH) through a transpeptidation reaction involving GSH polymerisation. PCs chelate Cd ions in the cytosol, forming stable Cd-PC complexes that are then transported into the vacuole for sequestration; the review names this cytosol-to-vacuole pathway as the central PC-mediated detoxification axis and notes that PCS activity and gene expression are regulated at both transcriptional and post-transcriptional levels.

Genetic-manipulation strategy taxonomy (Table 1)

The review’s central artefact is Table 1, an 80-row matrix that catalogues for each study the overall experimental genetic approach, the genes/loci/allelic series involved, the examples of main findings related to PCs in Cd-exposed plants, and the citation. The strategies covered are:

• Cd-sensitive mutant isolation and characterisation: the CAD1 locus and the cad1-1 through cad1-6 allelic series in Arabidopsis thaliana, including the foundational result that cad1-3 (most sensitive) shows no detectable PCs upon Cd exposure and that BSO (a PC biosynthesis inhibitor) does not further sensitise cad1-3 but does sensitise wild type.
• Forward genetics in cad1-3 background: isolation of additional Cd-hypersensitive mutants such as PP2A-4C and IAR4, identifying PC-independent mechanisms of Cd tolerance modulated by PP2A and downstream signalling/biosynthesis.
• PCS overexpression in homologous and heterologous host systems: AtPCS1 overexpression in Arabidopsis, Nicotiana tabacum, Brassica juncea, Nicotiana glauca, and rice; TaPCS1 (wheat) overexpression in A. thaliana, tobacco, and rice; OsPCS1, OsPCS2, OsPCS5, OsPCS15 overexpression in Arabidopsis or rice; heterologous expression of MpPCS (Marchantia polymorpha), ZmPCS1 (maize), SepPCS (Sedum plumbizincicola), anaPCS (cyanobacterial Anabaena PCC 7120), CdPCS1 (Cynodon dactylon), VsPCS1 (Vicia sativa), NnPCS1 (Nelumbo nucifera), PaPCS (Phragmites australis), ThPCS1 (Tamarix hispida), BnPCS1 (Boehmeria nivea), and the duplicated BnPCS paralogues from Brassica napus; and a Caenorhabditis elegans CePCS rescue of cad1-3.
• PCS silencing strategies: seed-specific RNAi against OsPCS1 in rice (≈50% Cd reduction in rice seeds in one study, ≈51% Cd reduction in rice grains via endosperm-specific GluC promoter silencing of OsPCS1+OsPCS2 in another), RNAi-mediated silencing of OsPCS2 under the constitutive maize ubiquitin1 promoter (PC reduction without major Cd-tolerance change), CRISPR/Cas9 knockout of MpPCS in Marchantia polymorpha, T-DNA insertion mutants in rice (pcs1), and virus-induced gene silencing (VIGS) of PCS in tomato.
• Vacuolar-transport coupling: characterisation of AtABCC1, AtABCC2, AtABCC3 (AtMRP3) knockouts and double-mutants showing reduced vacuolar Cd-PC sequestration; AtABCC3 overexpression can complement an atabcc1 atabcc2 double knockout in the presence of PCs.
• Multigene and combined strategies: simultaneous overexpression of AsPCS1 + GSH1, AsPCS1 + YCF1, SpGSH1 + SpPCS1 (Spirodela polyrhiza), and co-overexpression of OsPCS1 + OsABCC1 + OsHMA3 (reducing both arsenic and Cd in rice grains).
• Synthetic-peptide and analogue strategies: synthetic pseudo-phytochelatin transgenes (Postrigan et al.), a PC-like peptide (PCL) with α-Glu-Cys linkage (Zheng et al.), and a pph6his gene encoding an α-peptide-linkage PC analogue (Vershinina et al.).
• Hormonal and transcription-factor coupling: AtWRKY45 identified as a positive regulator of Cd tolerance via PCS1/PCS2 upregulation in Arabidopsis; melatonin enhancement of Cd tolerance in tomato via PCS and COMT regulation of PC biosynthesis (Xing et al.).

The full row-level detail is in the source’s Table 1 and is not reproduced exhaustively here; the wiki’s mitigation page will draw selectively.

Bibliometric methodology and the resulting databases

Section 3 reports a Web of Science Core Collection search using VOSviewer 1.6.15 to map the field. The search-and-filter flowchart in Figure 2 records the following counts at each filter step:

• Web of Science Topic search ("cadmium" OR "Cd") AND ("phytochelatins") returned n = 1395 records.
• Adding ("plant" OR "crop") reduced this to n = 1185.
• Excluding ("algae" OR "algae") (the source presents both terms; this is a string repetition in the source’s flowchart) reduced this to n = 1075.
• The mutant-focused subset (AND "mutant*" NOT "transgenic*") returned n = 93, reduced to n = 39 after manual selection and deletion.
• The transgenic-focused subset (AND "transgenic*" NOT "mutant*") returned n = 89, reduced to n = 44 after manual selection and deletion.

The two final databases (n = 39 mutant studies, n = 44 transgenic studies) feed the country/institution/author co-occurrence networks in Figures 3 (mutant subset) and 4 (transgenic subset). The country-network analysis identifies China, USA, Germany, France, Australia, Sweden, Italy, Hungary, Poland, Switzerland, Slovakia, Czech Republic, and South Korea as the leading contributing countries in the mutant subset and a partially overlapping set (USA, China, Italy, South Korea, Spain, France, Bangladesh, Russia, Singapore, Tunisia, Japan, Thailand, India, Australia, Germany, Pakistan, Czech Republic, Sweden, Slovakia) in the transgenic subset; the institution and author networks are reported in Figures 3B/C and 4B/C and are not transcribed here. Keyword co-occurrence (Figure 3D for mutant subset, Figure 4D for transgenic subset) recovers terms including Cadmium, Phytochelatin, Glutathione, Antioxidants, Metal homeostasis, Sulfate transporter, Hyperaccumulators, Transgenic, Liquid Chromatography, Brassica juncea L., Phragmites australis, Pteris vittata, and Cysteine synthase.

Headline takeaways the authors emphasise

• Overexpression of PCS1 in Arabidopsis and other species frequently produces increased PC content but does NOT reliably translate to increased Cd tolerance — several studies (e.g., AtPCS1 under the CaMV 35S promoter; ectopic AtPCS1 overexpression under its own promoter; cytosolic-targeted AtPCS1; AdPCS2/AdPCS3 from Arundo donax) report Cd hypersensitivity rather than improvement. The authors attribute this paradox to PC toxicity at high concentrations, cytosolic accumulation of Cd-PC complexes exceeding vacuolar-sequestration capacity, GSH depletion, oxidative stress, or interference with alternative detoxification pathways.
• PCS2 in Arabidopsis is endogenously expressed at low levels and cannot complement cad1-3 hypersensitivity even when overexpressed under standard promoters; constitutive PCS2 overexpression partially rescues cad1-3 on soil and reduces PC3 levels compared to PCS1 overexpression. AtPCS2 is also detected in the nucleus and tightly transcriptionally regulated, suggesting roles beyond PC biosynthesis.
• The cad1-3 knockout (deficient in AtPCS1) does not show photosynthetic damage under Cd stress, whereas nramp3nramp4 (defective in vacuolar metal remobilisation) does — implying vacuolar metal stores protect plastid function during Cd and oxidative stress and motivating compensatory-pathway exploration when PCS function is impaired.
• The bibliometric analysis flags an opportunity to expand from model species (Arabidopsis thaliana, Nicotiana tabacum) to agriculturally relevant crops or species with high phytoremediation potential. The authors also call for tone-and-context analysis in future bibliometric work to surface whether the literature presents a balanced view of benefits and risks of genetic manipulation of the PC pathway.
• The authors’ own research group is “working on the integration of grafting” with omics approaches to dissect root vs shoot contributions to Cd tolerance and accumulation, framed as a translational step before deployment in food crops.

Methods (brief)

This is a narrative perspective article with an embedded bibliometric analysis. The narrative synthesis surveys the published literature on PCS-based genetic manipulation for Cd mitigation in plants and tabulates ~80 studies in Table 1; selection criteria are not formally stated and the authors do not declare a PRISMA flow, inclusion/exclusion criteria, or risk-of-bias assessment for the narrative portion.

The bibliometric portion uses the Web of Science Core Collection, accessed via a Topic-field search with the strings recorded in Figure 2’s flowchart (see “Bibliometric methodology” above for the filter steps and counts). Manual selection and deletion reduced the two automated subsets (mutant: 93 → 39; transgenic: 89 → 44) into the final databases. VOSviewer 1.6.15 generated the co-authorship and keyword co-occurrence networks (Figures 3A–D and 4A–D). Microsoft Excel handled the data export and curation step. Supplementary Material S1 hosts Tables S1–S10 with the detailed bibliometric outputs.

The journal (IJMS, MDPI) is open-access; the article is published under CC BY 4.0. The Author Contributions block credits D.N.M. with conceptualisation, formal analysis, investigation, writing original draft, writing review/editing, and visualisation; C.C.T. with formal analysis, investigation, and visualisation; R.A.A. with writing review/editing and supervision (the contributions appear continued past page 16 in the PDF and are not transcribed in full here). Academic Editor: Tarek Alshaal. Received 20 April 2025; revised 12 May 2025; accepted 14 May 2025; published 16 May 2025. The DOI 10.3390/ijms26104767 resolves to Int. J. Mol. Sci. 2025, Vol 26, Article 4767.

Implications

• Certification: The review contributes no occurrence data and no exposure data, so it does not move any HMTc threshold-setting work. Its value for HMTc is indirect — it is biological background for the question of whether plant-side genetic engineering of the PC pathway is a credible Cd-reduction lever for crops that supply HMTc-certifying categories (rice, leafy vegetables, root vegetables, cacao). The review’s own framing emphasises that PCS-only strategies are insufficient and that multigene precision engineering combining PCS with vacuolar transporters is the more credible direction.
• App: No routing to ingredient or product pages. The review provides background reading for the cadmium page on the topic of plant-side detoxification mechanisms and remediation/food-safety strategies; it does not bear on contamination occurrence in any specific food or personal-care matrix.
• Courses: Useful as a single-source orientation to the PCS-Cd genetic-engineering literature, the cad1 allelic-series vocabulary, the bidirectional outcomes of PCS overexpression, and the multigene/grafting future directions. Should not be cited as the authority for any specific quantitative crop-level Cd-reduction claim; trace claims to the cited primary studies first (e.g., Gui et al., Li et al., Xing et al., Chen et al.).
• Microbiome: Marginally relevant. The review mentions “Microorganisms” as a contextual element in Figure 1 (“PC-related Cd Mitigation in Plants”) and notes that microbial-fermentation-derived PC strategies are a route, but does not engage the gut microbiome or the heavy-metal-microbiome axis. WikiBiome federation is unlikely to draw on this source.

Limitations

This is a narrative perspective article with no declared inclusion/exclusion criteria for the narrative synthesis, no PRISMA flow, and no risk-of-bias assessment. The bibliometric portion uses a single database (Web of Science Core Collection) and a single search-and-filter flow; Scopus, PubMed, and CNKI are not consulted, which biases the country/institution networks toward English-language and Web of Science-indexed publications. The “n = 1075” denominator after excluding algae captures studies on land plants but does not separate model plants from agriculturally relevant crops, and the final n = 39 and n = 44 subsets are small enough that the co-occurrence networks in Figures 3 and 4 are sensitive to the manual-selection step (the source does not document selection criteria for “Manual selection and deletion”). The review focuses on Cd as the metal of interest; lead, arsenic, mercury, chromium, nickel, and tin — all of which appear in the broader PC literature and on the HMTc 10-analyte priority list — are mentioned only incidentally (e.g., a single Gui et al. line on arsenic-and-Cd grain reduction). The review’s geographic and crop scope is uneven: rice, Arabidopsis, tobacco, and B. juncea dominate; cacao, leafy vegetables, root vegetables, and the cereals beyond rice/wheat are not treated.

Wiki pages this source may touch

• cadmium
• remediation-evidence

Verification notes

Existing-page check. DOI grep (10.3390/ijms26104767), raw_handle grep (MFK_03-phytochelatins-and-cadmium-mitigation-harnessin), and cite-key glob (marques2025-*) over wiki/sources/ on 2026-06-08 returned no matches. The single marques20* hit (marques2021-trace-elements-milks-plant-based-drinks) is a different paper. This is a NEW source page — no prior version to merge-enhance.

Evidence tier. B (secondary narrative perspective with bibliometric component). The paper reports no primary measurements, declares no systematic search strategy for the narrative portion, and uses a single-database bibliometric portion without PRISMA. A-tier is reserved for primary peer-reviewed studies and authoritative agency monographs; this is neither.

Metals frontmatter. Cd only. From the HMTc 10-analyte priority list (Pb, tAs, Cd, MeHg, tHg, iAs, Ni, Al, Cr-VI, Sn), only cadmium is the subject of this review. The paper mentions arsenic once in passing (Gui et al. co-overexpression study) and copper once (the cad1-3 altered copper transport finding) but does not provide synthesis material on any non-Cd metal. The metals abbreviation Cd is used per CLAUDE.md Part 14 vocabulary.

Ingredients, products, matrices, jurisdictions frontmatter. All empty. The source measures nothing in any food matrix; the only species names with food relevance (rice, wheat, Brassica juncea mustard, Nicotiana tabacum tobacco, Boehmeria nivea ramie) appear as model or transgenic host organisms in genetic-engineering experiments, not as sampled food commodities with reported Cd concentrations. Brazil is the authors’ institutional country but the review is conceptually international and no national regulatory or occurrence frame applies, so jurisdictions: remains empty.

Sample size. Null. The narrative portion has no sampling frame; the bibliometric portion reports paper counts (1395 → 1185 → 1075 → 93/89 → 39/44) rather than human/biological samples. sample_n represents the latter and is null here.

Brand firewall (Part 12). No commercial brand names appear in the source body for contamination values. The methodology names VOSviewer (software, version 1.6.15), Microsoft Excel, and the Web of Science Core Collection (Clarivate database); per the verification checklist’s Exception 2, scientific-method software and database vendor names are permitted in methods context. No firewall action required.

HMTc firewall (Part 2). The review contains no HMTc-threshold language, no claims about HMI certification levels, and no consumer-audience risk advisories. It does contain forward-looking framing about “food safety” and “Cd-contaminated agricultural environments” as research goals, and recommends multigene precision engineering as a route to “balancing detoxification efficiency with agronomic performance”; this is biological-research framing, not a wiki-side synthesis or threshold proposal, and is preserved in the Implications section without escalation. No firewall action required.

Date arithmetic. Received 20 April 2025, revised 12 May 2025, accepted 14 May 2025, published 16 May 2025 — all consistent with the year: 2025 frontmatter. DOI 10.3390/ijms26104767 resolves to Int. J. Mol. Sci. 2025, Vol 26, Article 4767.

Reviewer’s note on scope fit. This paper is in the “Black Market Peptide Metal Survey / heavy_metals_peptides” Manual Fetch Kimi folder alongside luo2024-peptides-heavy-metal-remediation and shalev2022-peptide-metal-nmr-review. Per the 2026-06-02 commit 3f47f95 — scope: mitigation/remediation is in-scope, not a skip, peptide-mediated mitigation/remediation papers are in scope as background for the mitigation-evidence chapter. This paper’s wiki contribution is narrower than Luo 2024’s (Luo covers peptide-metal remediation across multiple metals and remediation modalities; Marques is Cd-only and is restricted to the PC pathway in plants) and is methodologically distinct from Shalev 2022’s (NMR characterisation of peptide-metal complexes). Karen’s manual-fetch curation is assembling a peptide-metal corpus likely intended to underpin a future PC-and-MT mitigation chapter; this paper is a focused contributor on the PC-genetic-engineering axis of that chapter.

Slug-vocabulary note. [[mitigation/remediation-evidence]] is not in the 2026-05-18 taxonomy snapshot. This is the same snapshot-coverage gap noted in luo2024-peptides-heavy-metal-remediation and shalev2022-peptide-metal-nmr-review; the wikilink points to the wiki’s mitigation/remediation-evidence section and is in-scope per the cited 2026-06-02 scope commit. No correction applied; the snapshot will catch up in a future refresh.

Audit subagent (2026-06-08) verdict: PROMOTE. Five checks (numerical fidelity, slug vocabulary, speciation/methods, brand firewall, HMTc firewall) returned four ✅ and one ⚠️.

• Check 1 numerical-fidelity ✅. Subagent independently verified the Web of Science filter chain 1395 → 1185 → 1075 → 93/89 → 39/44 against the Figure 2 flowchart, the ≈50% (row [65] OsPCS1 RNAi in rice seeds) and ≈51% (row [71] OsPCS1+OsPCS2 endosperm GluC-promoter silencing) Cd-reduction percentages against Table 1, the VOSviewer 1.6.15 version against p.13, the DOI 10.3390/ijms26104767 → Vol 26 Article 4767 against the citation block, the receipt/revision/acceptance/publication dates against p.1, and the gene/locus list (cad1-1 through cad1-6, AtPCS1/AtPCS2, OsPCS1/OsPCS2/OsPCS5/OsPCS15, TaPCS1, MpPCS, ZmPCS1, NtPCS1, AtABCC1/2/3, HMA2/HMA4, AsPCS1+GSH1, AsPCS1+YCF1, SpGSH1+SpPCS1, OsPCS1+OsABCC1+OsHMA3) against Table 1 row-by-row, with no invented entries detected. The Table 1 row count “~80” is a within-tolerance approximation of the ~76 distinct study rows the subagent counted by inspection.
• Check 2 slug-vocabulary ⚠️ on [[mitigation/remediation-evidence]] not in the 2026-05-18 snapshot — same snapshot-coverage gap as the Luo 2024 and Shalev 2022 siblings, already disclosed in the slug-vocabulary note above and accepted per Luo precedent. No content correction applied.
• Checks 3 (speciation/methods), 4 (Part 12 brand firewall), and 5 (Part 2 wiki/HMTc firewall) all ✅. Subagent verified that arsenic and copper appear only as incidental mentions in the Gui et al. and cad1-3 phenotype rows respectively and do not rise to synthesis-level coverage warranting frontmatter inclusion, that the Methods (brief) section does not invent analytical instruments or LODs, that no commercial food/personal-care brand names appear, and that the Implications section does not propose HMTc thresholds or issue consumer risk advisories. 1 finding flagged, 0 corrections applied (the ⚠️ was a known cross-page taxonomy gap, not a defect on this page), 0 rejected. Audit subagent ID a3f323fbaa5d5301d.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.