Functional Assessment of an Overexpressed Arabidopsis Purple Acid Phosphatase Gene (AtPAP26) in Tobacco Plants

Functional assessment of AtPAP17; encoding a purple acid phosphatase involved in phosphate metabolism in Arabidopsis thaliana

PURPOSE

Purple acid phosphatases (PAPs) includ the largest classes of non-specific plant acid phosphatases. Most characterized PAPs were found to play physiological functions in phosphorus metabolism. In this study, we investigated the function of AtPAP17 gene encoding an important purple acid phosphatase in Arabidopsis thaliana.

METHODS

The full-length cDNA sequence of AtPAP17 gene under the control of CaMV-35S promoter was transferred to the A. thaliana WT plant. The generated homozygote AtPAP17-overexpressed plants were compared by the types of analyses with corresponding homozygote atpap17-mutant plant and WT in both + P (1.2 mM) and - P (0 mM) conditions.

RESULTS

In the + P condition, the highest and the lowest amount of Pi was observed in AtPAP17-overexpressed plants and atpap17-mutant plants by 111% increase and 38% decrease compared with the WT plants, respectively. Furthermore, under the same condition, APase activity of AtPAP17-overexpressed plants increased by 24% compared to the WT. Inversely, atpap17-mutant plant represented a 71% fall compared to WT plants. The comparison of fresh weight and dry weight in the studied plants showed that the highest and the lowest amount of absorbed water belonged to OE plants (with 38 and 12 mg plant^-1) and Mu plants (with 22 and 7 mg plant^-1) in + P and - P conditions, respectively.

CONCLUSION

The lack of AtPAP17 gene in the A. thaliana genome led to a remarkable reduction in the development of root biomass. Thus, AtPAP17 could have an important role in the root but not shoot developmental and structural programming. Consequently, this function enables them to absorb more water and eventually associated with more phosphate absorption.

Adaptive strategies of plants to conserve internal phosphorus under P deficient condition to improve P utilization efficiency

Phosphorus (P) is one of the limiting factors for plant growth and productivity due to its slow diffusion and immobilization in the soil which necessitates application of phosphatic fertilizers to meet the crop demand and obtain maximum yields. However, plants have evolved mechanisms to adapt to low P stress conditions either by increasing acquisition (alteration of belowground processes) or by internal inorganic P (Pi) utilization (cellular Pi homeostasis) or both. In this review, we have discussed the adaptive strategies that conserve the use of P and maintain cellular Pi homeostasis in the cytoplasm. These strategies involve modification in membrane lipid composition, flavanol/anthocyanin level, scavenging and reutilization of Pi adsorbed in cell wall pectin, remobilization of Pi during senescence by enzymes like RNases and purple acid phosphatases, alternative mitochondrial electron transport, and glycolytic pathways. The remobilization of Pi from senescing tissues and its internal redistribution to various cellular organelles is mediated by various Pi transporters. Although much efforts have been made to enhance P acquisition efficiency, an understanding of the physiological mechanisms conserving internal Pi and their manipulation would be useful for plants that can utilize P more efficiently to produce optimum growth per unit P uptake.

Water-Soluble Carbon Dots in Cigarette Mainstream Smoke: Their Properties and the Behavioural, Neuroendocrinological, and Neurotransmitter Changes They Induce in Mice

BACKGROUND

It is well known that smoking is harmful to health; however, it can also ameliorate anxiety. To date, it is unclear whether any nanoparticles found in cigarette mainstream smoke (CS) contribute to this effect.

AIM

The aim of this study was to assess the particle composition of CS to identify novel anti-anxiety components.

METHODS

Carbon dots (CDs) from CS (CS-CDs) were characterised using high-resolution transmission electron microscopy, Fourier-transform infrared, ultraviolet, fluorescence, X-ray photoelectron spectroscopy, X-ray diffraction and high-performance liquid chromatography. The anti-anxiety effects of CS-CDs in mouse models were evaluated and confirmed with the elevated plus maze and open-field tests.

RESULTS

The quantum yield of CS-CDs was 13.74%, with a composition of C, O, and N. In addition, the surface groups contained O-H, C-H, C=O, C-N, N-H, C-O-C, and COO- bonds. Acute toxicity testing revealed that CS-CDs had low in vitro and in vivo toxicity within a certain concentration range. The results of the elevated plus maze and open-field tests showed that CS-CDs had a significant anti-anxiety effect and a certain sedative effect in mice. The mechanism of these effects may be related to the decrease in glutamate levels and promotion of norepinephrine production in the mouse brain, and the decrease in dopamine in mouse serum due to CS-CDs.

CONCLUSION

CS-CDs may have anti-anxiety and certain sedative effects. This study provides a new perspective for a more comprehensive understanding of the components, properties, and functions of CS. Furthermore, it offers a novel target for the development of smoking cessation treatments, such as nicotine replacement therapy.

Identification and Functional Analysis of Two Purple Acid Phosphatases AtPAP17 and AtPAP26 Involved in Salt Tolerance in Arabidopsis thaliana Plant

Tolerance to salinity is a complex genetic trait including numerous physiological processes, such as metabolic pathways and gene networks; thereby, identification of genes indirectly affecting, as well as those directly influencing, is of utmost importance. In this study, we identified and elucidated the functional characterization of AtPAP17 and AtPAP26 genes, as two novel purple acid phosphatases associated with high-salt tolerance in NaCl-stressed conditions. Here, the overexpression of both genes enhanced the expression level of AtSOS1, AtSOS2, AtSOS3, AtHKT1, AtVPV1, and AtNHX1 genes, involving in the K+/Na+ homeostasis pathway. The improved expression of the genes led to facilitating intracellular Na+ homeostasis and decreasing the ion-specific damages occurred in overexpressed genotypes (OEs). An increase in potassium content and K+/Na+ ratio was observed in OE17 and OE26 genotypes as well; however, lower content of sodium accumulated in these plants at 150 mM NaCl. The overexpression of these two genes resulted in the upregulation of the activity of the catalase, guaiacol peroxidase, and ascorbate peroxidase. Consequently, the overexpressed plants showed the lower levels of hydrogen peroxide where the lowest amount of lipid peroxidation occurred in these lines. Besides the oxidation resistance, the boost of the osmotic regulation through the increased proline and glycine-betaine coupled with a higher content of pigments and carbohydrates resulted in significantly enhancing biomass production and yield in the OEs under 150 mM NaCl. High-salt stress was also responsible for a sharp induction on the expression of both PAP17 and PAP26 genes. Our results support the hypothesis that these two phosphatases are involved in plant responses to salt stress by APase activity and/or non-APase activity thereof. The overexpression of PAP17 and PAP26 could result in increasing the intracellular APase activity in both OEs, which exhibited significant increases in the total phosphate and free Pi content compared to the wild-type plants. Opposite results witnessed in mutant genotypes (Mu17, Mu26, and DM), associating with the loss of AtPAP17 and AtPAP26 functions, clearly confirmed the role of these two genes in salt tolerance. Hence, these genes can be used as candidate genes in molecular breeding approaches to improve the salinity tolerance of crop plants.

Recent insights into the metabolic adaptations of phosphorus-deprived plants

Inorganic phosphate (Pi) is an essential macronutrient required for many fundamental processes in plants, including photosynthesis and respiration, as well as nucleic acid, protein, and membrane phospholipid synthesis. The huge use of Pi-containing fertilizers in agriculture demonstrates that the soluble Pi levels of most soils are suboptimal for crop growth. This review explores recent advances concerning the understanding of adaptive metabolic processes that plants have evolved to alleviate the negative impact of nutritional Pi deficiency. Plant Pi starvation responses arise from complex signaling pathways that integrate altered gene expression with post-transcriptional and post-translational mechanisms. The resultant remodeling of the transcriptome, proteome, and metabolome enhances the efficiency of root Pi acquisition from the soil, as well as the use of assimilated Pi throughout the plant. We emphasize how the up-regulation of high-affinity Pi transporters and intra- and extracellular Pi scavenging and recycling enzymes, organic acid anion efflux, membrane remodeling, and the remarkable flexibility of plant metabolism and bioenergetics contribute to the survival of Pi-deficient plants. This research field is enabling the development of a broad range of innovative and promising strategies for engineering phosphorus-efficient crops. Such cultivars are urgently needed to reduce inputs of unsustainable and non-renewable Pi fertilizers for maximum agronomic benefit and long-term global food security and ecosystem preservation.

The Critical Role of AtPAP17 and AtPAP26 Genes in Arabidopsis Phosphate Compensation Network

Purple acid phosphatases (PAP)-encoding genes form a complex network that play a critical role in plant phosphate (Pi) homeostasis. Mostly, the functions of PAPs were investigated individually. However, the interactions of most of these genes in response to various concentrations of available Pi remain unknown. In this study, the roles of AtPAP17 and AtPAP26 genes, and their relationship within Pi homeostasis context were investigated. Surprisingly, atpap17 and atpap26 mutants not only showed no obvious developmental defects, but also produced higher biomass in compare to wild type (WT) plants under normal growth conditions. Comparing gene expression patterns of these mutants with WT plant, we identified a set of genes up-regulated in mutant plants but not in WT. Based on these unexpected results and up-regulation of AtPAP17 and AtPAP26 genes by the loss of function of each other, the hypothesis of compensation relationship between these genes in Pi homeostasis was assessed by generating atpap17/atpap26 double mutants. Observation of developmental defects in atpap17/atpap26 mutant but not in single mutants indicated a compensation relationship between AtPAP17 and AtPAP26 genes in Pi homeostasis network. Taken together, these results demonstrate the activation of AtPAP17 and AtPAP26 genes to buffer against the loss of function of each other, and this compensation relationship is vital for Arabidopsis growth and development.

Heterologous expression of an acid phosphatase gene and phosphate limitation leads to substantial production of chicoric acid in Echinacea purpurea transgenic hairy roots

A high level of the secondary metabolite chicoric acid is produced by intracellular Pi supply and extracellular phosphate limiting in Echinacea purpurea hairy roots. Chicoric acid (CA) is a secondary metabolite which is gained from Echinacea purpurea. It has been found to be one of the most potent HIV integrase inhibitors with antioxidant and anti-inflammatory activities. However, the low-biosynthesis level of this valuable compound becomes an inevitable obstacle limiting further commercialization. Environmental stresses, such as phosphorus (Pi) deficiency, stimulate the synthesis of chemical metabolites, but significantly reduce plant growth and biomass production. To overcome the paradox of dual opposite effect of Pi limitation, we examined the hypothesis that the intracellular Pi supply and phosphate-limiting conditions enhance the total CA production in E. purpurea hairy roots. For this purpose, the coding sequence (CDS) of a purple acid phosphatase gene from Arabidopsis thaliana, AtPAP26, under CaMV-35S promoter was overexpressed in E. purpurea using Agrobacterium rhizogenes strain R15834. The transgenic hairy roots were cultured in a Pi-sufficient condition to increase the cellular phosphate metabolism. A short-term Pi starvation treatment of extracellular phosphate was applied to stimulate genes involved in CA biosynthesis pathway. The overexpression of AtPAP26 gene significantly increased the total APase activity in transgenic hairy roots compared to the non-transgenic roots under Pi-sufficient condition. Also, the transgenic hairy roots showed increase in the level of total and free phosphate, and in root fresh and dry weights compared to the controls. In addition, the phosphate limitation led to significant increase in the expression level of the CA biosynthesis genes. Considering the increase of biomass production in transgenic vs. non-transgenic hairy roots, a 16-fold increase was obtained in the final yield of CA for transgenic E. purpurea roots grown under -P condition compared to +P non-transgenic roots. Our results suggested that the expression of phosphatase genes and phosphate limitation were significantly effective in enhancing the final production yield and large-scale production of desired secondary metabolites in medicinal plant hairy roots.