Adenosine 5′-phosphosulfate reductase (APR2) mutation inArabidopsisimplicates glutathione deficiency in selenate toxicity

Abstract

APR2 is the dominant APR (adenosine 5'-phosphosulfate reductase) in the model plant Arabidopsis thaliana, and converts activated sulfate to sulfite, a key reaction in the sulfate reduction pathway. To determine whether APR2 has a role in selenium tolerance and metabolism, a mutant Arabidopsis line (apr2-1) was studied. apr2-1 plants had decreased selenate tolerance and photosynthetic efficiency. Sulfur metabolism was perturbed in apr2-1 plants grown on selenate, as observed by an increase in total sulfur and sulfate, and a 2-fold decrease in glutathione concentration. The altered sulfur metabolism in apr2-1 grown on selenate did not reflect typical sulfate starvation, as cysteine and methionine levels were increased. Knockout of APR2 also increased the accumulation of total selenium and selenate. However, the accumulation of selenite and selenium incorporation in protein was lower in apr2-1 mutants. Decreased incorporation of selenium in protein is typically associated with increased selenium tolerance in plants. However, because the apr2-1 mutant exhibited decreased tolerance to selenate, we propose that selenium toxicity can also be caused by selenate's disruption of glutathione biosynthesis leading to enhanced levels of damaging ROS (reactive oxygen species).

Alleviation Effect of Selenium on Manganese Stress of Plants

“…Se (in the forms of sodium selenate and sodium selenite) has two opposing effects on lettuce plant metabolism: at low doses it acts as an antioxidant and enhances plant growth, whereas at higher levels it reduces yields [26]. Selenium toxicity in high doses was also confirmed by other authors [49,50].…”

An Overview of Selenium Uptake, Metabolism, and Toxicity in Plants

“…Generally, under Se stress decreased level of glutathione is observed (Hugouvieux et al, 2009), except in Se-tolerant plants where elevated levels are observed (Grant et al, 2011). In another study by Grant et al (2011) on cad2-1 mutant plants having defective glutathione synthetic pathway showed many folds decreased root length as compared to wild type plants grown on 20 μM selenate. In apr2-1 mutant of Arabidopsis , glutathione depletion and ROS accumulation found to be interlinked to each other under Se stress (Grant et al, 2011).…”

Stuck between a ROS and a hard place: Analysis of the ubiquitin proteasome pathway in selenocysteine treated Brassica napus reveals different toxicities during selenium assimilation

“…For example, APR2 regulates both the assimilation of sulfur (Loudet et al, 2007) and selenium (Grant et al, 2011;Chao et al, 2014) in Arabidopsis. Intriguingly, apr2-1 mutants had decreased Se in protein, but were still Se sensitive due to the accumulation of selenate that caused an accumulation of superoxide.…”