Abstract
BackgroundAmong cereals, durum wheat (Triticum turgidum L. subsp. durum) accumulates cadmium (Cd) at higher concentration if grown in Cd-polluted soils. Since cadmium accumulation is a risk for human health, the international trade organizations have limited the acceptable concentration of Cd in edible crops. Therefore, durum wheat cultivars accumulating low cadmium in grains should be preferred by farmers and consumers. To identify the response of durum wheat to the presence of Cd, the transcriptomes of roots and shoots of Creso and Svevo cultivars were sequenced after a 50-day exposure to 0.5 μM Cd in hydroponic solution.ResultsNo phytotoxic effects or biomass reduction was observed in Creso and Svevo plants at this Cd concentration. Despite this null effect, cadmium was accumulated in root tissues, in shoots and in grains suggesting a good cadmium translocation rate among tissues. The mRNA sequencing revealed a general transcriptome rearrangement after Cd treatment and more than 7000 genes were found differentially expressed in root and shoot tissues. Among these, the up-regulated genes in roots showed a clear correlation with cadmium uptake and detoxification. In particular, about three hundred genes were commonly up-regulated in Creso and Svevo roots suggesting a well defined molecular strategy characterized by the transcriptomic activation of several transcription factors mainly belonging to bHLH and WRKY families. bHLHs are probably the activators of the strong up-regulation of three NAS genes, responsible for the synthesis of the phytosiderophore nicotianamine (NA). Moreover, we found the overall up-regulation of the methionine salvage pathway that is tightly connected with NA synthesis and supply the S-adenosyl methionine necessary for NA biosynthesis. Finally, several vacuolar NA chelating heavy metal transporters were vigorously activated.ConclusionsIn conclusion, the exposure of durum wheat to cadmium activates in roots a complex gene network involved in cadmium translocation and detoxification from heavy metals. These findings are confident with a role of nicotianamine and methionine salvage pathway in the accumulation of cadmium in durum wheat.
Highlights
Among cereals, durum wheat (Triticum turgidum L. subsp. durum) accumulates cadmium (Cd) at higher concentration if grown in Cd-polluted soils
The same samples were analyzed by atomic absorption (GF-AAS) to quantify the level of accumulated Cd in roots and shoots: as expected, Cd concentration is higher in roots than in shoots (Fig. 2)
In particular we found transcriptional factors belonging to WRKY-family (AT5G24110 – WRKY DNA-binding protein 30 (WRKY30), AT4G23810 – WRKY DNA-binding protein 53 (WRKY53) and AT2G38470 – WRKY DNA-binding protein 33 (WRKY33)), basic/helix-loop-helix (AT3G56970 – bHLH38/ORG2, AT3G47640 – bHLH47/ PYE and AT2G28160 - bHLH29/FIT), one belongs to Ethylene responsive factor (ERF) family (AT3G20310 – ethylene response factor 7 (ERF7)) as well as one transcriptional repressor involved in abiotic stress response (AT1G27730 – ZAT10)
Summary
Durum wheat (Triticum turgidum L. subsp. durum) accumulates cadmium (Cd) at higher concentration if grown in Cd-polluted soils. Durum) accumulates cadmium (Cd) at higher concentration if grown in Cd-polluted soils. Plant species could accumulate cadmium when grown on polluted soils [3]. The genetic traits involved in Cd accumulation were well defined in durum wheat and a single locus (Cdu1) explaining 80% of the variability was identified [8, 9]. Wiebe [10] found a perfect match between the HMA3-B1 gene (coding a P1B-ATPase transporter) and the Cdu locus. He sequenced HMA3-B1 from high and low Cd accumulator durum wheat cvs discovering a 17 bp duplication in high-Cd genotypes causing a premature stop codon and a severely truncated protein, suggesting HMA3 as the best
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