Genetic Control of the Response to Sulfur, Nitrogen, and Phosphorus Supply in Arabidopsis thaliana

Sulfur deficiency is a relatively new problem in Europe and the studies on sulfur use efficiency are still lagging behind those on the other major nutrients such as nitrogen or phosphorus. Therefore, the main aim of this work was to improve the understanding of the sulfate assimilation pathway, its regulation and interaction with other elements. In the course of this project natural variation was used to characterise further the regulation of the pathway and to identify new regulatory components. This analysis revealed that the first two enzymes involved in sulfate reduction – ATP sulfurylase and APS reductase – are nearly equally involved in its control but through different mechanisms. Moreover, a Genome-Wide Association Study was conducted on the accumulation of nitrate, phosphate, and sulfate in more than 200 arabidopsis accessions. This analysis resulted in identification of new functions of already known genes which were not previously related to plant nutrition. Additionally, previously undescribed genes were identified disruption of which results in changes in the anion accumulation phenotype. To characterise arabidopsis response to sulfate and/or nitrate deficiency a collection of genetically divergent accessions grown under different nutrition regimes was examined for a number of morphological and metabolic traits. This analysis resulted in dissection of four different patterns of plant response to sulfate availability. Individual accessions were characterised as best adapted to nutrient deficiency. Traits such as biomass allocation or root architecture were suggested as potential targets in the process of developing new crop varieties. This analysis is unique since, to my knowledge, it is the first one which provides the characterisation of arabidopsis response to nutrient availability based on the analysis of such a large number (25) of natural accessions. The results described here provided new insight into sulfate metabolism and can be used to develop new breeding strategies and improve crop yield and quality

Variation in sulfur and selenium accumulation is controlled by naturally occurring isoforms of the key sulfur assimilation enzyme ADENOSINE 5′-PHOSPHOSULFATE REDUCTASE2 across the arabidopsis species range

Natural variation allows the investigation of both the fundamental functions of genes and their role in local adaptation. As one of the essential macronutrients, sulfur is vital for plant growth and development and also for crop yield and quality. Selenium and sulfur are assimilated by the same process, and although plants do not require selenium, plant-based selenium is an important source of this essential element for animals. Here, we report the use of linkage mapping in synthetic F2 populations and complementation to investigate the genetic architecture of variation in total leaf sulfur and selenium concentrations in a diverse set of Arabidopsis (Arabidopsis thaliana) accessions. We identify in accessions collected from Sweden and the Czech Republic two variants of the enzyme ADENOSINE 5′-PHOSPHOSULFATE REDUCTASE2 (APR2) with strongly diminished catalytic capacity. APR2 is a key enzyme in both sulfate and selenate reduction, and its reduced activity in the loss-of-function allele apr2-1 and the two Arabidopsis accessions Hodonín and Shahdara leads to a lowering of sulfur flux from sulfate into the reduced sulfur compounds, cysteine and glutathione, and into proteins, concomitant with an increase in the accumulation of sulfate in leaves. We conclude from our observation, and the previously identified weak allele of APR2 from the Shahdara accession collected in Tadjikistan, that the catalytic capacity of APR2 varies by 4 orders of magnitude across the Arabidopsis species range, driving significant differences in sulfur and selenium metabolism. The selective benefit, if any, of this large variation remains to be explored

Natural Variation in the ATPS1 Isoform of ATP Sulfurylase Contributes to the Control of Sulfate Levels in Arabidopsis

Sulfur is an essential macronutrient for all living organisms. Plants take up inorganic sulfate from the soil, reduce it, and assimilate it into bioorganic compounds, but part of this sulfate is stored in the vacuoles. In our first attempt to identify genes involved in the control of sulfate content in the leaves, we reported that a quantitative trait locus (QTL) for sulfate content in Arabidopsis (Arabidopsis thaliana) was underlain by the APR2 isoform of the key enzyme of sulfate assimilation, adenosine 5'-phosphosulfate reductase. To increase the knowledge of the control of this trait, we cloned a second QTL from the same analysis. Surprisingly, the gene underlying this QTL encodes the ATPS1 isoform of the enzyme ATP sulfurylase, which precedes adenosine 5'-phosphosulfate reductase in the sulfate assimilation pathway. Plants with the Bay allele of ATPS1 accumulate lower steady-state levels of ATPS1 transcript than those with the Sha allele, which leads to lower enzyme activity and, ultimately, the accumulation of sulfate. Our results show that the transcript variation is controlled in cis. Examination of ATPS1 sequences of Bay-0 and Shahdara identified two deletions in the first intron and immediately downstream the gene in Bay-0 shared with multiple other Arabidopsis accessions. The average ATPS1 transcript levels are lower in these accessions than in those without the deletions, while sulfate levels are significantly higher. Thus, sulfate content in Arabidopsis is controlled by two genes encoding subsequent enzymes in the sulfate assimilation pathway but using different mechanisms, variation in amino acid sequence and variation in expression levels