Characterization of Selenium Accumulation, Localization and Speciation in Buckwheat–Implications for Biofortification

Buckwheat is an important crop species in areas of selenium (Se) deficiency. To obtain better insight into their Se metabolic properties, common buckwheat (Fagopyrum esculentum) and tartary buckwheat (F. tataricum) were supplied with different concentrations of Se, supplied as selenate, selenite, or Astragalus bisulcatus plant extract (methyl-selenocysteine). Se was supplied at different developmental stages, with different durations, and in the presence or absence of potentially competing ions, sulfate, and phosphate. The plants were analyzed for growth, Se uptake, translocation, accumulation, as well as for Se localization and chemical speciation in the seed. Plants of both buckwheat species were supplied with 20 μM of either of the three forms of Se twice over their growth period. Both species accumulated 15–40 mg Se kg−1 DW in seeds, leaves and stems, from all three selenocompounds. X-ray microprobe analysis showed that the Se in seeds was localized in the embryo, in organic C-Se-C form(s) resembling selenomethionine, methyl-selenocysteine, and γ-glutamyl-methylselenocysteine standards. In short-term (2 and 24 h) Se uptake studies, both buckwheat species showed higher Se uptake rate and shoot Se accumulation when supplied with plant extract (methyl-selenocysteine), compared to selenite or selenate. In long-term (7 days) uptake studies, both species were resistant to selenite up to 50 μM. Tartary buckwheat was also resistant to selenate up to 75 μM Se, but >30 μM selenate inhibited common buckwheat growth. Selenium accumulation was similar in both species. When selenite was supplied, Se levels were 10–20-fold higher in root (up to 900 mg Se kg−1 DW) than shoot, but 4-fold higher in shoot (up to 1,200 mg Se kg−1 DW) than root for selenate-supplied plants. Additionally, sulfate and phosphate supply affected Se uptake, and conversely selenate enhanced S and P accumulation in both species. These findings have relevance for crop Se biofortification applications

Identification of Consensus Regions Associated with Shoot Biomass Production in the Medicago

International audienceIdentification of common genome regions influencing biomass production in multiple Medicago populations can establish focal points for implementing future marker-assisted breeding approaches to improve alfalfa (M. sativa L.) forage yield and facilitate identification of candidate genes. The goal of this study was to identify consensus regions associated with biomass production and candidate genes within the context of the M. truncatula Gaertn. genome, based on previous reports of 83 biomass-affiliated markers and 30 quantitative trait loci (QTL) detected among one M. truncatula and four M. sativa biparental and association mapping populations. The genome positions for 68 markers and all 30 biomass QTL were determined. Ten consensus regions associated with Medicago forage yield in two or more populations were identified. The level of resolution for these regions, however, was not sufficient to clearly identify potential causal candidate genes. Consequently, a targeted set of 208 loci influencing Arabidopsis growth and development were surveyed for their positions in the Medicago genome to identify those which colocalized with biomass markers and QTL intervals. Among 233 homologous genes identified, 51 were located within consensus biomass regions. Potential genes affecting Medicago forage yield variation included those affiliated with phytohormone biosynthesis, transport, and signaling; light responsive developmental phase transitions; and microRNA-mediated regulation of gene expression. These outcomes provide insight into genetic factors that researchers may wish to target for future validation experiments, and for designing marker-assisted breeding strategies to improve alfalfa productivity

Comparison of ATP sulfurylase 2 from selenium hyperaccumulator Stanleya pinnata and non-accumulator Stanleya elata reveals differential intracellular localization and enzyme activity levels

Background: The plant Stanleya pinnata hyperaccumulates Se up to 0.5% of its dry weight in organic forms, whereas the closely related Stanleya elata does not hyperaccumulate Se. ATP sulfurylase (ATPS) can catalyze the formation of adenosine 5′-phosphoselenate (APSe) from ATP and selenate. We investigated the S. pinnata ATPS2 isoform (SpATPS2) to assess its possible role in Se hyperaccumulation. Methods: ATPS expression and activity was compared in the two Stanleya species. The ATPS2 protein sequences were modeled. Sub-cellular locations were analyzed using GFP fusions. Enzyme activity of purified recombinant SpATPS2 was measured. Results: ATPS2 transcript levels were six-fold higher in roots of S. pinnata relative to S. elata. Overall root ATPS enzyme activity was two-fold elevated in S. pinnata. Cloning and sequencing of SpATPS2 and S. elata ATPS2 (SeATPS2) showed the predicted SeATPS2 to be canonical, while SpATPS2, although very similar in its core structure, has unique features, including an interrupted plastid targeting signal due to a stop codon in the 5′ region of the coding sequence. Indeed GFP fusions revealed that SpATPS2 had exclusive cytosolic localization, while SeATPS2 showed dual localization in plastids and cytosol. SpATPS2 activity was inhibited by both sulfate and selenate, indicating that the enzyme acts on both substrates. Conclusions: The ATPS2 from S. pinnata differs from non-accumulator ATPS2 in its elevated expression and sub-cellular localization. It likely acts on both selente and sulfate substrates. General significance: These observations shed new light on the role of ATPS2 in the evolution of Se hyperaccumulation in plants. This article is part of a Special Issue entitled Selenium research in biochemistry and biophysics - 200 year anniversary issue, edited by Dr. Elias Arnér and Dr. Regina Brigelius-Flohe. © 2018 Elsevier B.V