Sulfur Deficiency Increases Phosphate Accumulation, Uptake, and Transport in Arabidopsis thaliana

Reviewing impacts of biotic and abiotic stresses on the regulation of phosphate homeostasis in plants

Adapting to varying phosphate levels in the environment is vital for plant growth. The PHR1 phosphate starvation response transcription factor family, along with SPX inhibitors, plays a pivotal role in plant phosphate responses. However, this regulatory hub intricately links with diverse biotic and abiotic signaling pathways, as outlined in this review. Understanding these intricate networks is crucial, not only on a fundamental level but also for practical applications, such as enhancing sustainable agriculture and optimizing fertilizer efficiency. This comprehensive review explores the multifaceted connections between phosphate homeostasis and environmental stressors, including various biotic factors, such as symbiotic mycorrhizal associations and beneficial root-colonizing fungi. The complex coordination between phosphate starvation responses and the immune system are explored, and the relationship between phosphate and nitrate regulation in agriculture are discussed. Overall, this review highlights the complex interactions governing phosphate homeostasis in plants, emphasizing its importance for sustainable agriculture and nutrient management to contribute to environmental conservation.

Sulfate supplementation affects nutrient and photosynthetic status of Arabidopsis thaliana and Nicotiana tabacum differently under prolonged exposure to cadmium

Hydroponic experiments were performed to examine the effect of prolonged sulfate limitation combined with cadmium (Cd) exposure in Arabidopsis thaliana and a potential Cd hyperaccumulator, Nicotiana tabacum. Low sulfate treatments (20 and 40 µM MgSO₄) and Cd stress (4 µM CdCl₂) showed adverse effects on morphology, photosynthetic and biochemical parameters and the nutritional status of both species. For example, Cd stress decreased NO₃^- root content under 20 µM MgSO₄ to approximately 50% compared with respective controls. Interestingly, changes in many measured parameters, such as chlorophyll and carotenoid contents, the concentrations of anions, nutrients and Cd, induced by low sulfate supply, Cd exposure or a combination of both factors, were species-specific. Our data showed opposing effects of Cd exposure on Ca, Fe, Mn, Cu and Zn levels in roots of the studied plants. In A. thaliana, levels of glutathione, phytochelatins and glucosinolates demonstrated their distinct involvement in response to sub-optimal growth conditions and Cd stress. In shoot, the levels of phytochelatins and glucosinolates in the organic sulfur fraction were not dependent on sulfate supply under Cd stress. Altogether, our data showed both common and species-specific features of the complex plant response to prolonged sulfate deprivation and/or Cd exposure.

The SLIM1 transcription factor is required for arsenic resistance in Arabidopsis thaliana

The transcriptional regulators of arsenic-induced gene expression remain largely unknown. Sulfur assimilation is tightly linked with arsenic detoxification. Here, we report that mutant alleles in the SLIM1 transcription factor are substantially more sensitive to arsenic than cadmium. Arsenic treatment caused high levels of oxidative stress in the slim1 mutants, and slim1 alleles were impaired in both thiol accumulation and sulfate accumulation. We further found enhanced arsenic accumulation in roots of slim1 mutants. Transcriptome analyses indicate an important role for SLIM1 in arsenic-induced tolerance mechanisms. The present study identifies the SLIM1 transcription factor as an essential component in arsenic tolerance and arsenic-induced gene expression. Our results suggest that the severe arsenic sensitivity of the slim1 mutants is caused by altered redox status.

Plants on Rich-Magnesium Dolomite Barrens: A Global Phenomenon

For botanists and ecologists, the close link between some plants and substrates, such as serpentine or gypsum, is well known. However, the relationship between dolomite and its flora has been much less studied, due to various causes. Its diffuse separation from limestone and the use of a vague approach and terminology that, until now, no one has tried to harmonize are among these reasons. After carrying out an extensive review, completed with data on the distribution of plants linked to dolomite, the territories in which this type of flora appears at a global level were mapped using a geographic information system software. In addition, data on soils were collected, as well as on their influence on the ionomic profile of the flora. These data were completed with the authors' own information from previous research, which also served to assess these communities' degree of conservation and the genetic diversity of some of their characteristic species. The results showed that the so-called "dolomite phenomenon" is widely represented and is clearly manifested in the appearance of a peculiar flora, very rich in endemisms, on dry soils, poor in nutrients, and with a high Mg level. Although dolomite habitats cause adaptations in plants which are even more recognizable than those of other rock types, they have not been widely studied from an ecological, evolutionary, and conservation point of view because, so far, neither their characteristics nor their universal demarcation have been precisely defined.

Sulfur Homeostasis in Plants

Sulfur (S) is an essential macronutrient for plant growth and development. S is majorly absorbed as sulfate from soil, and is then translocated to plastids in leaves, where it is assimilated into organic products. Cysteine (Cys) is the first organic product generated from S, and it is used as a precursor to synthesize many S-containing metabolites with important biological functions, such as glutathione (GSH) and methionine (Met). The reduction of sulfate takes place in a two-step reaction involving a variety of enzymes. Sulfate transporters (SULTRs) are responsible for the absorption of SO42- from the soil and the transport of SO42- in plants. There are 12-16 members in the S transporter family, which is divided into five categories based on coding sequence homology and biochemical functions. When exposed to S deficiency, plants will alter a series of morphological and physiological processes. Adaptive strategies, including cis-acting elements, transcription factors, non-coding microRNAs, and phytohormones, have evolved in plants to respond to S deficiency. In addition, there is crosstalk between S and other nutrients in plants. In this review, we summarize the recent progress in understanding the mechanisms underlying S homeostasis in plants.

The Effect of Amending Soil with Waste Elemental Sulfur on the Availability of Selected Macroelements and Heavy Metals

Elemental sulfur of waste origin may be a valuable sulfur source for plants. However, assessing the suitability of environmental use of a waste material should confirm there is no harmful effect of the material on soil environment. The purpose of the incubation experiment was to assess the availability of selected elements (P, K, Ca, Mg, Fe, Mn, Zn, Cu, Cr, Ni, Pb, Cd) in soils supplemented with waste elemental sulfur. The research was conducted on two soils: light and heavy, and with three sulfur doses applied to each soil. Available forms of elements in the soils were extracted 60 days after the waste introduction, with three reagents: 0.01 mol L−1 CaCl2, Mehlich 3 and 1 mol L−1 HCl. Additionally, to determine the impact of the introduced sulfur on soil acidification, soil pH was periodically checked during the experiment. The sulfur addition intensified acidification of the light soil, and, to a lesser extent, of the heavy soil. The acidifying effect was stronger when the sulfur dose was higher. The content of available forms of elements in the soils depended mainly on the strength of the used extractants (generally, the highest amounts were extracted with 1 mol L−1 HCl and the lowest with 0.01 mol L−1 CaCl2). The effect of sulfur introduction on element availability was small. No harmful effect on element availability in soils was stated.

Transcriptomic analysis at organ and time scale reveals gene regulatory networks controlling the sulfate starvation response of Solanum lycopersicum

BACKGROUND

Sulfur is a major component of biological molecules and thus an essential element for plants. Deficiency of sulfate, the main source of sulfur in soils, negatively influences plant growth and crop yield. The effect of sulfate deficiency on plants has been well characterized at the physiological, transcriptomic and metabolomic levels in Arabidopsis thaliana and a limited number of crop plants. However, we still lack a thorough understanding of the molecular mechanisms and regulatory networks underlying sulfate deficiency in most plants. In this work we analyzed the impact of sulfate starvation on the transcriptome of tomato plants to identify regulatory networks and key transcriptional regulators at a temporal and organ scale.

RESULTS

Sulfate starvation reduces the growth of roots and leaves which is accompanied by major changes in the organ transcriptome, with the response being temporally earlier in roots than leaves. Comparative analysis showed that a major part of the Arabidopsis and tomato transcriptomic response to sulfate starvation is conserved between these plants and allowed for the identification of processes specifically regulated in tomato at the transcript level, including the control of internal phosphate levels. Integrative gene network analysis uncovered key transcription factors controlling the temporal expression of genes involved in sulfate assimilation, as well as cell cycle, cell division and photosynthesis during sulfate starvation in tomato roots and leaves. Interestingly, one of these transcription factors presents a high identity with SULFUR LIMITATION1, a central component of the sulfate starvation response in Arabidopsis.

CONCLUSIONS

Together, our results provide the first comprehensive catalog of sulfate-responsive genes in tomato, as well as novel regulatory targets for future functional analyses in tomato and other crops.