Expression of Sailx suchowensis SsIRT9 enhances cadmium accumulation and alters metal homeostasis in tobacco.

Cadmium (Cd) contamination in soils is of great concern for plant growth and human health. Willow (Salix spp.) is a promising phytoextractor because of its high biomass production. However, as a non-hyperaccumulator, willow has a low competitive ability in extraction of Cd. Thus, improving Cd concentrations in developing tissues is one of the primary tasks. Here, our study uncovers a novel SsIRT9 gene from Sailx suchowensis which manipulates plant Cd accumulation. SsIRT9 was more highly expressed in willow roots than other SsIRT genes. As a plasma membrane-localized protein, when expressed in yeast, SsIRT9 retarded cell growth more severely than other SsIRT proteins in the presence of Cd. Furthermore, SsIRT9 was cloned and expressed in tobacco and SsIRT9 did not affect plant growth. In hydroponic experiments, SsIRT9 lines displayed higher Cd in the shoots than the wild type. When grown in Cd-contaminated soils, Cd levels in transgenic tobacco increased by 152-364% in roots and by 135-444% in shoots, demonstrating significant superiority in Cd accumulation over other functional IRT/ZIP transporters. Moreover, expressing SsIRT9 in tobacco altered metal homeostasis, especially manganese and zinc. Taken together, we envision that SsIRT9 expression in plants is a promising strategy for upgrading extraction of Cd from soils.

Assessment of the capability of cadmium accumulation and translocation among 31 willows: four patterns of willow biomass variation response to cadmium.

Cadmium (Cd) pollution threatens food security and the environment. Willow species (Salix, Salicaceae) exhibit a remarkable potential to restore Cd-polluted sites due to their high biomass production and high Cd accumulation capacities. This study examined the Cd accumulation and tolerance in 31 genotypes of shrub willow in hydroponic conditions at varying Cd levels (0 µM Cd, 5 µM Cd, and 20 µM Cd). The root, stem, and leaf biomass of 31 shrub willow genotypes showed significant differences to Cd exposure. Among 31 willow genotypes, four patterns of biomass variation response to Cd were identified: insensitive to Cd; growth inhibition due to excessive Cd supply (high Cd inhibition); low Cd causing inhibited growth, whereas high Cd leading to increased biomass (U-shape); and growth increment with excessive Cd exposure (high Cd induction). The genotypes belonging to the "insensitive to Cd" and/or "high Cd induction" were candidates for the utilization of phytoremediation. Based on the analysis of Cd accumulation of 31 shrub willow genotypes at high and low Cd levels, genotypes 2372, 51-3, and 1052 obtained from a cross between S. albertii and S. argyracea grew well and accumulated relatively more Cd levels than other genotypes. In addition, for Cd-treated seedlings, root Cd accumulation was positively correlated with shoot Cd accumulation and total Cd uptake, demonstrating that Cd accumulation in roots could serve as a biomarker for evaluating the Cd extraction capacity of willows, especially in hydroponics screening. The results of this study screened out willow genotypes with high Cd uptake and translocation capacities, which will provide valuable approaches for restoring Cd-contaminated soils with willows.