The domestication of wild emmer wheat led to the selection of modern durum wheat, grown mainly for pasta production. We describe the 10.45 gigabase (Gb) assembly of the genome of durum wheat cultivar Svevo. The assembly enabled genome-wide genetic diversity analyses revealing the changes imposed by thousands of years of empirical selection and breeding. Regions exhibiting strong signatures of genetic divergence associated with domestication and breeding were widespread in the genome with several major diversity losses in the pericentromeric regions. A locus on chromosome 5B carries a gene encoding a metal transporter (TdHMA3-B1) with a non-functional variant causing high accumulation of cadmium in grain. The high-cadmium allele, widespread among durum cultivars but undetected in wild emmer accessions, increased in frequency from domesticated emmer to modern durum wheat. The rapid cloning of TdHMA3-B1 rescues a wild beneficial allele and demonstrates the practical use of the Svevo genome for wheat improvement.

NaCl stress is a major abiotic stress limiting the productivity and the geographical distribution of many plant species. Roots are the primary site of salinity perception. To understand better NaCl stress responses in Arabidopsis roots, a comparative proteomic analysis of roots that had been exposed to 150 mM NaCl for either 6 h or 48 h was conducted. Changes in the abundance of protein species within roots were examined using two-dimensional electrophoresis. Among the >1000 protein spots reproducibly detected on each gel, the abundance of 112 protein spots decreased and 103 increased, at one or both time points, in response to NaCl treatment. Through liquid-chromatography–tandem mass spectrometry, identity was assigned to 86 of the differentially abundant spots. The proteins identified included many previously characterized stress-responsive proteins and others related to processes including scavenging for reactive oxygen species; signal transduction; translation, cell wall biosynthesis, protein translation, processing and degradation; and metabolism of energy, amino acids, and hormones. At the resolution of individual genes and proteins, poor statistical correlation (6 h, r= –0.13; 48 h, r=0.11) of these protein expression data with previous microarray results was detected, supporting the concept that post-transcriptional regulation plays an important role in stress-responsive gene expression, and highlighting the need for combined transcriptomic and proteomic analyses.

Concentrations of cadmium (Cd) in the grain of many durum wheats (Triticum turgidum subsp. durum) grown in North American prairie soils often exceed international trade standards. Genotypic differences in root-to-shoot translocation of Cd are a major determinant of intraspecific variation in the accumulation of Cd in grain. We tested the extent to which changes in whole-plant Cd accumulation and the distribution of Cd between tissues influences Cd accumulation in grain by measuring Cd accumulation throughout the grain filling period in two near-isogenic lines (NILs) of durum wheat that differ in grain Cd accumulation.

Cadmium accumulation in grain of durum wheat (Triticum turgidum L. var. durum) represents a concern to consumers. In an effort to understand the regulation of Cd accumulation in maturing grain, the remobilization of ¹⁰⁹Cd applied to stem and flag leaves was examined in two near‐isogenic lines that differ in grain Cd accumulation. Absorbed ¹⁰⁹Cd was primarily retained in the labelling flap (50–54% and 65–80% for stem and flag leaves, respectively). Cadmium exported from the stem flap initially (3 d) accumulated in the stem in a declining gradient towards the head. Subsequent remobilization of Cd deposited in the stem was associated with Cd accumulation in the grain. Cadmium exported from the flag leaf flap was primarily directed to the grain. Little (<1%) Cd accumulated in the glumes or rachis, and transport of Cd to shoot tissues below the flag leaf node was low (<1%). On average, 9% and 17% of absorbed ¹⁰⁹Cd accumulated in the grain 14 d after labelling the stem and flag leaf, respectively. Irrespective of labelling position, the low Cd‐accumulating isoline averaged 1.5–2‐fold lower Cd accumulation per grain and Cd concentration in the grain than the high Cd‐accumulating isoline. Cadmium accumulation in the grain was inversely correlated with Cd retention in the stem (stem labelled) and labelling flap (flag leaf labelled) for both isolines. Cadmium translocation to the grain was not inhibited by Zn when both were applied simultaneously (50 pM ¹⁰⁹Cd; 0.5 μM ⁶⁵Zn) to the flag leaf. These results show that elevated remobilization of Cd from the leaves and stem to the maturing grain may be partially responsible for the high accumulation of Cd in durum wheat grain.

Cadmium (Cd) concentrations in durum wheat (Triticum turgidum L. var durum) grain grown in North American prairie soils often exceed proposed international trade standards. To understand the physiological processes responsible for elevated Cd accumulation in shoots and grain, Cd uptake and translocation were studied in seedlings of a pair of near-isogenic durum wheat lines, high and low for Cd accumulation in grain. In short-term studies (<3 h) using 109Cd-labelled nutrient solutions, there were no differences between lines in time- or concentration-dependent 109Cd accumulation by roots. In contrast, rates of 109Cd translocation from roots to shoots following longer exposure (48-60 h) were 1.8-fold higher in the high Cd-accumulating line, despite equal whole-plant 109Cd accumulation in the lines. Over the same period, the 109Cd concentration in root-pressure xylem exudates was 1.7 to 1.9-fold higher in the high Cd-accumulating line. There were no differences between the lines in 65Zn accumulation or partitioning that could account for the difference between lines in 109Cd translocation. These results suggest that restricted root-to-shoot Cd translocation may limit Cd accumulation in durum wheat grain by directly controlling Cd translocation from roots during grain filling, or by controlling the size of shoot Cd pools that can be remobilised to the grain.