Variation of Cicer Germplasm to Manganese Toxicity Tolerance

Reproducibility, reliability, and regulatory relevance of plant visual injury assessments

The registration of herbicides in the European Union requires an assessment of risks to nontarget terrestrial plants (NTTPs). Regulatory plant studies are performed to determine risk-assessment-relevant endpoints (50% effect rate) for quantitative parameters, mostly biomass and survival. Recently, the European Food Safety Authority stated that endpoints for qualitatively assessed plant visual injuries (PVIs) such as necrosis, chlorosis, and so forth should be considered for the risk assessment as equal to endpoints derived from quantitatively determined parameters. However, the lack of guidance in the NTTP test guidelines on how to assess PVI and how to derive a statistically meaningful endpoint for PVI makes their use in risk assessments challenging. To evaluate and improve the reliability, reproducibility, and regulatory relevance of PVI assessments in NTTP studies, the PVI Working Group was formed in 2022 within the SETAC Plant Interest Group. In a first exercise, research needs, guidance gaps, and shortcomings in current methodologies were identified and are presented together with recommendations for a future, validated, and harmonized method for the assessment of PVI. Survey results revealed a high variability in how PVI are currently assessed, and that the reliability of these data is unclear. Under current conditions, the PVI data can rather be seen as supportive information instead of using the data for the statistically sound determination of a regulatory endpoint. Consequently, standardization and harmonization of procedures for the assessment of PVI are needed. An improved scoring methodology should be developed that allows for a precise, statistically sound endpoint determination. Regarding the regulatory relevance of PVI, further research is required to assess the biological meaning of PVI data and how this is connected to the regulatory requirements and protection goals. Last but not least, guidance is required on how to evaluate the historically available PVI data that are based on various assessment methodologies. Integr Environ Assess Manag 2024;20:915-923. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Transcriptomic, epigenomic and physiological comparisons reveal key factors for different manganese tolerances in three Chenopodium ambrosioides L. populations

Chenopodium ambrosioides is a manganese (Mn) hyperaccumulator that can be used for Mn-polluted soil phytoremediation. However, the mechanism of Mn tolerance of C. ambrosioides remains largely unknown. In this study, the key factors for Mn tolerance of C. ambrosioides was investigated from the aspects of DNA methylation pattern, gene expression regulation and physiological function. We found that the two genotypes of C. ambrosioides populations have differentiated tolerance to Mn stress (Mn-tolerant: CS and XC, Mn-sensitive: WH). Although there was no difference in Mn accumulation between two types under excess Mn, the biomass and photosynthetic systems were more severely inhibited in Mn-sensitive type, as well as suffering more serious oxidative damage. More differentially expressed genes (DEGs) were downregulated in the Mn-tolerant type, indicating that the Mn-tolerant type tends to inhibit gene expression to cope with Mn stress. DEGs related to metal transport, antioxidant system, phytohormone and transcription factors contribute to the tolerance of C. ambrosioides to Mn, and account for difference in Mn stress sensitivities between the Mn-sensitive and tolerant types. We also found that DNA methylation variation may help to cope with Mn stress. The global DNA methylation level in C. ambrosioides increased under Mn stress, especially in the Mn-sensitive type. Dozens of methylated loci were significantly associated with the Mn accumulation trait of C. ambrosioides, and some critical DEGs were regulated by DNA methylation. Our study comprehensively demonstrated the Mn tolerance mechanism of C. ambrosioides for the first time, and highlighted the roles of epigenetic modification in C. ambrosioides response to Mn stress. Our findings may contribute to elucidating the adaptation mechanism of hyperaccumulator to the heavy metal toxicity.

Identification of two chickpea multidrug and toxic compound extrusion transporter genes transcriptionally upregulated upon aluminum treatment in root tips

Aluminum (Al) toxicity poses a significant challenge for the yield improvement of chickpea, which is an economically important legume crop with high nutritional value in human diets. The genetic basis of Al-tolerance in chickpea remains unclear. Here, we assessed the Al-tolerance of 8 wild Cicer and one cultivated chickpea (PBA Pistol) accessions by measuring the root elongation in solution culture under control (0 μM Al³⁺) and Al treatments (15, 30 μM Al³⁺). Compared to PBA Pistol, the wild Cicer accessions displayed both tolerant and sensitive phenotypes, supporting wild Cicer as a potential genetic pool for Al-tolerance improvement. To identify potential genes related to Al-tolerance in chickpea, genome-wide screening of multidrug and toxic compound extrusion (MATE) encoding genes was performed. Fifty-six MATE genes were identified in total, which can be divided into 4 major phylogenetic groups. Four chickpea MATE genes (CaMATE1-4) were clustered with the previously characterized citrate transporters MtMATE66 and MtMATE69 in Medicago truncatula. Transcriptome data showed that CaMATE1-4 have diverse expression profiles, with CaMATE2 being root-specific. qRT-PCR analyses confirmed that CaMATE2 and CaMATE4 were highly expressed in root tips and were up-regulated upon Al treatment in all chickpea lines. Further measurement of carboxylic acids showed that malonic acid, instead of malate or citrate, is the major extruded acid by Cicer spp. root. Protein structural modeling analyses revealed that CaMATE2 has a divergent substrate-binding cavity from Arabidopsis AtFRD3, which may explain the different acid-secretion profile for chickpea. Pangenome survey showed that CaMATE1-4 have much higher genetic diversity in wild Cicer than that in cultivated chickpea. This first identification of CaMATE2 and CaMATE4 responsive to Al³⁺ treatment in Cicer paves the way for future functional characterization of MATE genes in Cicer spp., and to facilitate future design of gene-specific markers for Al-tolerant line selection in chickpea breeding programs.

Assessment of trace elements pollution and their potential health risks in the cobalt-nickel bearing areas of Lomié, East Cameroon

A study of trace elements pollution in the cobalt-nickel mining area of Nkamouna-Kongo (East Region of Cameroon) and their intimation to the risk of human exposure was carried out. A large spatial variability of concentrations was observed in the geochemical analysis of the trace elements in the thirty samples investigated. Trace element pollution in the investigated samples was assessed using the Regional Screening Level calculator of Environmental Protection Agency (USEPA) and the collected sample were analyzed using a SPECTRO XEPOS Energy Dispersive X-Ray Fluorescence analyzer (ED-XRF). The trace element concentrations in the analyzed samples followed the following order: Fe > Cr > Mn > Zr > Ni > Ba > Rb > Cu > Zn > Sr > Ga > Pb > Co > Rb > As > Sn. The averages of trace elements contamination factors followed a decreasing order:: Cr > Ni > Fe > As > Co > Cu > Zr > Ga > Pb > Mn > Zn > Y > Rb > Ba > Sn > Sr. Enrichment factor studies revealed that chromium (Cr) was severely enriched (indicating that Cr is the main element of the anthropic load) while elements such as Ni, Ba, Mn, Co, Cu, Zn, Ga, As, and Pb were moderately enriched. The associated health risk of human exposure was investigated using the Regional Screening Level of Environmental Protection Agency. It was found out that the carcinogenic risk to the exposed population from ingestion is high (2.5E-03), while the dermal risk is moderate (7.08E-04) and the inhalation risk is low (2.50E-07). The total non-carcinogenic risk from trace elements exposure for adults (HI = 1.5) and children (HI = 1.47E + 01) indicates that non-carcinogenic effects may occur in the vicinity of the study area.

Novel Sources of Tolerance to Aluminium Toxicity in Wild Cicer (Cicer reticulatum and Cicer echinospermum) Collections

In acid soils, the toxic form of aluminium, Al³⁺, significantly inhibits root growth and elongation, leading to less water and nutrient uptake. Previous research had shown differential Al toxicity tolerance among cultivated Cicer arietinum L. (chickpea); however, the potential for developing tolerant cultivars is limited by the narrow genetic diversity of cultivated chickpeas. Recent collections from Turkey of wild Cicer species, Cicer reticulatum, and Cicer echinospermum, have increased the available gene pool significantly, but there has been no large-scale screening of wild Cicer for acid tolerance or Al³⁺ toxicity tolerance. This study evaluated 167 wild Cicer and 17 Australian chickpea cultivars in a series of screenings under controlled growth conditions. The pH of 4.2 and Al concentrations of 15 and 60 μM Al were selected for large-scale screening based on dose response experiments in a low ionic strength nutrient solution. The change in root length showed better discrimination between tolerant and sensitive lines when compared with shoot and root dry weights and was used as a selection criterion. In a large-scale screening, 13 wild Cicer reticulatum accessions had a higher root tolerance index (≥50%), and eight had higher relative change in root length (≥40%) compared with PBA Monarch, which showed greater tolerance among the Australian domestic cultivars screened. In general, C. reticulatum species were found to be more tolerant than C. echinospermum, while genetic population groups Ret_5, Ret_6, and Ret_7 from Diyarbakir and Mardin Province were more tolerant than other groups. Among C. echinospermum, Ech_6 from the Siv-Diyar collection site of the Urfa Province showed better tolerance than other groups. In this first detailed screening of aluminium toxicity tolerance in the new wild Cicer collections, we identified accessions that were more tolerant than current domestic cultivars, providing promising germplasm for breeding programs to expand chickpea adaptation to acid soils.