Publications

Plants take up Ag₂S-NPs without a marked selectivity in regard to particle size and without substantial transformation during upward translocation.

Rice is a major dietary source of cadmium (Cd) and arsenic (As) for populations consuming rice as the staple food. Excessive Cd and As accumulation in rice grain is of great concern worldwide, especially in South China where soil contamination with heavy metals and metalloids is widespread. It is important to reduce Cd and As accumulation in rice grain through selection and breeding of cultivars accumulating low levels of Cd or As.To assess the genetic and environmental variations in the concentrations of Cd and As in rice grains, 471 locally adapted high-yielding rice cultivars were grown at three moderately contaminated sites in South China for two years. Cadmium and As concentrations in brown rice varied by 10 - 32 and 2.5 - 4 fold, respectively. Genotype (G), environment (E) and G x E interactions were highly significant factors explaining the variations. Brown rice Cd concentration was found to correlate positively with the heading date among different cultivars, whereas As concentration and heading date correlated negatively. There was a significant and negative correlation between grain Cd and As concentrations.Eight and 6 rice cultivars were identified as stable low accumulators of Cd and As, respectively, based on the multiple site and season trials. These cultivars are likely to be compliant with the grain Cd or As limits of the Chinese Food Safety Standards when grown in moderately contaminated paddy soils in South China.

Dimethylarsenate [DMAs(V)] is a common methylated arsenic (As) species in paddy soils and rice plants. It is more toxic to plants than inorganic As and can cause the physiological disorder straighthead disease in rice. The mechanisms underlying different resistance to DMAs(V) among rice cultivars are unclear. Here, we investigated the differences in DMAs(V) uptake, translocation and reduction, as well as the effects on the metabolome, between two rice cultivars. We found that the cultivar Mars was 11-times more resistant to DMAs(V) than Zhe733. Mars accumulated more DMAs(V) in the roots, whereas Zhe733 translocated more DMAs(V) to the shoots and reduced more DMAs(V) to DMAs(III). DMAs(III) was more toxic than DMAs(V). Using heterologous expression and in vitro enzyme assays, we showed that the glutathione-S-transferases OsGSTU17 and OsGSTU50 were able to reduce DMAs(V) to DMAs(III), and the two genes were expressed at higher levels in the shoot of Zhe733 than Mars. Metabolomic analysis of rice shoots indicated that glutathione (GSH) metabolism was perturbed by DMAs(V) toxicity in Zhe733. Addition of exogenous GSH significantly alleviated the toxicity of DMAs(V) to Zhe733. Taken together, the results suggest that root-to-shoot translocation and reduction of DMAs(V) to DMAs(III) are key factors underlying the cultivar difference in the resistance to DMAs(V) toxicity.

Inorganic arsenic (As) is highly toxic and ubiquitous in the environment. Inorganic As can be transformed by microbial methylation, which constitutes an important part of the As biogeochemical cycle. In this study, we investigated As biotransformation by Pseudomonas alcaligenes NBRC14159. P. alcaligenes was able to methylate arsenite [As(III)] rapidly to dimethylarsenate and small amounts of trimethylarsenic oxide. An arsenite S-adenosylmethionine methyltransferase, PaArsM, was identified and functionally characterized. PaArsM shares low similarities with other reported ArsM enzymes (<55%). When P. alcaligenes arsM gene (PaarsM) was disrupted, the mutant lost As methylation ability and became more sensitive to As(III). PaarsM was expressed in the absence of As(III) and the expression was further enhanced by As(III) exposure. Heterologous expression of PaarsM in an As-hypersensitive strain of Escherichia coli conferred As(III) resistance. Purified PaArsM protein methylated As(III) to dimethylarsenate as the main product in the medium and also produced dimethylarsine and trimethylarsine gases. We propose that PaArsM plays a role in As methylation and detoxification of As(III) and could be exploited in bioremediation of As-contaminated environments.

Microbial oxidation of environmental antimonite (Sb(III)) to antimonate (Sb(V)) is an antimony (Sb) detoxification mechanism.

Background and objectives The aim of this study was to construct near‐infrared reflectance spectroscopy (NIRS) models to test the contents of apparent amylose, total starch, and crude protein for both foxtail millet grain and dehusked millet grain. The construction of models is based on chemical values and optimized spectral data of 111 core foxtail millet germplasm materials after analyzation of partial least square (PLS) method with cross‐validation. Findings Model calibration showed that there was better fitting degree of dehusked millet grain than that of foxtail millet. The coefficient determination for calibration (Rc 2 ) of former is &gt;0.843, while that of latter is &gt;0.823. The coefficient determination of prediction (Rp 2 ) of each component ranged from 0.794 to 0.888 for foxtail millet grain and 0.833 to 0.970 for dehusked millet grain. Conclusions The constructed NIRS models of both samples can be used to rapidly test foxtail millet quality, and the nondestructive nature of foxtail millet grain‐based test (which maintains seed vigor) better meets the requirements of the breeding, although the accuracy needs to be further improved. Significance and novelty This study developed a rapid method to detect the main nutritional quality for foxtail millet using two different samples, which can be used in germplasm resource innovation and contribute to the acceleration of cereal breeding.

Summary Arsenic can be biomethylated to form a variety of organic arsenicals differing in toxicity and environmental mobility. Trivalent methylarsenite (MAs(III)) produced in the methylation process is more toxic than inorganic arsenite (As(III)). MAs(III) also serves as a primitive antibiotic and, consequently, some environmental microorganisms have evolved mechanisms to detoxify MAs(III). However, the mechanisms of MAs(III) detoxification are not well understood. In this study, we identified an arsenic resistance ( ars ) operon consisting of three genes, arsRVK , that contribute to MAs(III) resistance in Ensifer adhaerens ST2. ArsV is annotated as an NADPH‐dependent flavin monooxygenase with unknown function. Expression of arsV in the arsenic hypersensitive Escherichia coli strain AW3110 Δars conferred resistance to MAs(III) and the ability to oxidize MAs(III) to MAs(V). In the presence of NADPH and either FAD or FMN, purified ArsV protein was able to oxidize both MAs(III) to MAs(V) and Sb(III) to Sb(V). Genes with arsV ‐like sequences are widely present in soils and environmental bacteria. Metagenomic analysis of five paddy soils showed the abundance of arsV ‐like sequences of 0.12–0.25 ppm. These results demonstrate that ArsV is a novel enzyme for the detoxification of MAs(III) and Sb(III) and the genes encoding ArsV are widely present in soil bacteria.

Rice is a major dietary source of the toxic metal cadmium (Cd). Concentration of Cd in rice grain varies widely at the regional scale, and it is challenging to predict grain Cd concentration using soil properties. The lack of reliable predictive models hampers management of contaminated soils. Here, we conducted a three-year survey of 601 pairs of soil and rice samples at a regional scale. Approximately 78.3% of the soil samples exceeded the soil screening values for Cd in China, and 53.9% of rice grain samples exceeded the Chinese maximum permissible limit for Cd. Predictive models were developed using multiple linear regression and machine learning methods. The correlations between rice grain Cd and soil total Cd concentrations were poor (R2 < 0.17). Both linear regression and machine learning methods identified four key factors that significantly affect grain Cd concentrations, including Fe-Mn oxide bound Cd, soil pH, field soil moisture content, and the concentration of soil reducible Mn. The machine learning-based support vector machine (SVM) model showed the best performance (R2 = 0.87) in predicting grain Cd concentrations at a regional scale, followed by machine learning-based random forest (RF) model (R2 = 0.67), and back propagation neural network (BP-NN) model (R2 = 0.64). Scenario simulations revealed that liming soil to a target pH of 6.5 could be one of the most cost-effective approaches to reduce the exceedance of Cd in rice grain. Taken together, these results show that machine learning methods can be used to predict Cd concentration in rice grain reliably at a regional scale and to support soil management and safe rice production.

Cadmium (Cd) is highly toxic to most organisms, but some rare plant species can hyperaccumulate Cd in aboveground tissues without suffering from toxicity. The mechanism underlying Cd detoxification by hyperaccumulators is interesting but unclear. Here, the heavy metal ATPase 3 (SpHMA3) gene responsible for Cd detoxification was isolated from the Cd/zinc (Zn) hyperaccumulator Sedum plumbizincicola. RNA interference (RNAi)-mediated silencing and overexpression of SpHMA3 were induced to investigate its physiological functions in S. plumbizincicola and a nonhyperaccumulating ecotype of Sedum alfredii. Heterologous expression of SpHMA3 in Saccharomyces cerevisiae showed Cd-specific transport activity. SpHMA3 was highly expressed in the shoots and the protein was localized to the tonoplast. The SpHMA3-RNAi lines were hypersensitive to Cd but not to Zn, with the growth of shoots and young leaves being severely inhibited by Cd. Overexpressing SpHMA3 in the nonhyperaccumulating ecotype of S. alfredii greatly increased its tolerance to and accumulation of Cd, but not Zn. These results indicate that elevated expression of the tonoplast-localized SpHMA3 in the shoots plays an essential role in Cd detoxification, which contributes to the maintenance of the normal growth of young leaves of S. plumbizincicola in Cd-contaminated soils.