Molecular Responses to Cadmium Exposure in Two Contrasting Durum Wheat Genotypes

Abstract

Cadmium is a heavy metal that can be easily accumulated in durum wheat kernels and enter the human food chain. Two near-isogenic lines (NILs) with contrasting cadmium accumulation in grains, High-Cd or Low-Cd (H-Cd NIL and L-Cd NIL, respectively), were used to understand the Cd accumulation and transport mechanisms in durum wheat roots. Plants were cultivated in hydroponic solution, and cadmium concentrations in roots, shoots and grains were quantified. To evaluate the molecular mechanism activated in the two NILs, the transcriptomes of roots were analyzed. The observed response is complex and involves many genes and molecular mechanisms. We found that the gene sequences of two basic helix–loop–helix (bHLH) transcription factors (bHLH29 and bHLH38) differ between the two genotypes. In addition, the transporter Heavy Metal Tolerance 1 (HMT-1) is expressed only in the low-Cd genotype and many peroxidase genes are up-regulated only in the L-Cd NIL, suggesting ROS scavenging and root lignification as active responses to cadmium presence. Finally, we hypothesize that some aquaporins could enhance the Cd translocation from roots to shoots. The response to cadmium in durum wheat is therefore extremely complex and involves transcription factors, chelators, heavy metal transporters, peroxidases and aquaporins. All these new findings could help to elucidate the cadmium tolerance in wheat and address future breeding programs.

Effects of Cadmium on Root Morpho-Physiology of Durum Wheat

“…On the other side, the gene coding for the SNARE protein resulted down-regulated ( Figure 13 ); however, in the description associated with the annotation of this gene was reported the caption “SNARE associated Golgi protein family” suggesting that the gene codes for a SNARE protein involved in the fusion of vesicles with Golgi membranes; in this perspective, its down-regulation makes sense to favor vesicular transport toward the plasma membrane and exocytosis. Among the up-regulated genes, we also found the genes YSL2, IREG2, HMA5 and HMT1 ( Figure 10 ); the last three are well-known genes coding for transporters involved in Cd detoxification and tolerance in Arabidopsis ( Long et al, 2010 ; Park et al, 2012 ; Wu et al, 2012 ) and in durum wheat ( Sabella et al, 2021 ) while YSL2 codes for a nicotianamine transmembrane transporter ( Conte et al, 2013 ). Taken together, the presented data indicate that, in the cv.…”

“…The grain surfaces were sterilized, and seeds sprouted in Petri dishes covered with humified vermiculite. After sprouting (about 1 week in the dark and temperature at 8°C), seedlings were transplanted in cylindric pots ( h = 50 cm, Ø = 10 cm) filled with perlite, soaked with deionized water, and quickly moved to the hydroponic system as described by Sabella et al, 2021 . Three seedlings were planted in each pot, and, for each treatment, three tubes were assembled (three biological replicates).…”

A Survey of the Transcriptomic Resources in Durum Wheat: Stress Responses, Data Integration and Exploitation

“…Wheat, in particular, is highly vulnerable to Cd toxicity as it tends to accumulate Cd in the grain [ 61 ], thus affecting human health. As in other plant species, comparative transcriptomic studies on wheat roots revealed a multilevel coordination of Cd uptake, transport, sequestration and detoxification, both in durum [ 39 , 40 ] and bread wheat [ 62 ]. Recently, the transcriptomes of roots from two commercial durum cultivars and from two near isogenic lines with contrasting Cd accumulation in grains were analyzed [ 39 , 40 ], identifying the key genes and mechanisms involved.…”

“…As in other plant species, comparative transcriptomic studies on wheat roots revealed a multilevel coordination of Cd uptake, transport, sequestration and detoxification, both in durum [ 39 , 40 ] and bread wheat [ 62 ]. Recently, the transcriptomes of roots from two commercial durum cultivars and from two near isogenic lines with contrasting Cd accumulation in grains were analyzed [ 39 , 40 ], identifying the key genes and mechanisms involved. The mRNA sequencing of Creso and Svevo durum cultivars in response to Cd treatment identified about 7100 DEGs in root and shoot tissues, revealing a conserved strategy to detoxify cells from Cd [ 39 ].…”

“…The elucidation of stress response mechanisms guide the development of breeding strategies or genetic modifications to obtain cultivars that do not translocate Cd up to the grains [ 63 ]. The transcriptome of roots of two Cd-treated or untreated low-Cd and high-Cd near-isogenic lines of durum wheat, accumulating Cd in grains, was carried out to reveal elements differentiating the low-Cd lines involved in Cd compartmentalization at the root level and genes expressed only in high-Cd lines acting in Cd translocation from root to shoot [ 40 ]. Two contigs annotated as aquaporins (pip1-2-like and aquaporin 1-5) were found to be expressed only in high-Cd lines and not in low-Cd lines, facilitating water transport, and hence Cd translocation.…”