Trade-offs between root-secreted acid phosphatase and root morphology traits, and their contribution to phosphorus acquisition in Brassica napus.

Oilseed rape (Brassica napus) is one of the most important oil crops in the world and shows sensitivity to low phosphorus (P) availability. In many soils, organic P (Po) is the main component of the soil P pool. Po must be mineralised to Pi through phosphatases, and then taken up by plants. However, the relationship between root-secreted acid phosphatases (APase) and root morphology traits, two important P-acquisition strategies in response to P deficiency, is unclear among B. napus genotypes. This study aimed to understand their relationship and how they affect P acquisition, which is crucial for the sustainable utilisation of agricultural P resources. This study showed significant genotypic variations in root-secreted APase activity per unit root fresh weight (SAP) and total root-secreted APase activity per plant (total SAP) among 350 B. napus genotypes. Seed yield was positively correlated with total SAP but not significantly correlated with SAP. Six root traits of 18 B. napus genotypes with contrasting root biomass were compared under normal Pi, low Pi and Po. Genotypes with longer total root length (TRL) reduced SAP, but those with shorter TRL increased SAP under P deficiency. Additionally, TRL was important in P-acquisition under three P treatments, and total SAP was also important in P-acquisition under Po treatment. In conclusion, trade-offs existed between the two P-acquisition strategies among B. napus genotypes under P-deficient conditions. Total SAP was an important root trait under Po conditions. These results might help to breed B. napus with greater P-acquisition ability under low P availability conditions.

Multi-omics analysis reveals the roles of purple acid phosphatases in organic phosphorus utilization by the tropical legume Stylosanthes guianensis.

Stylo (Stylosanthes guianensis) is a tropical legume known for its exceptional tolerance to low phosphate (Pi), a trait believed to be linked to its high acid phosphatase (APase) activity. Previous studies have observed genotypic variations in APase activity in stylo; however, the gene encoding the crucial APase responsible for this variation remains unidentified. In this study, transcriptomic and proteomic analyses were employed to identify eight Pi starvation-inducible (PSI) APases belonging to the purple APase (PAP) family in the roots of stylo and seven in the leaves. Among these PSI-PAPs, SgPAP7 exhibited a significantly positive correlation in its expression levels with the activities of both internal APase and root-associated APase across 20 stylo genotypes under low-Pi conditions. Furthermore, the recombinant SgPAP7 displayed high catalytic activity toward adenosine 5'-diphosphate (ADP) and phosphoenolpyruvate (PEP) in vitro. Overexpression (OE) of SgPAP7 in Arabidopsis facilitated exogenous organic phosphorus utilization. Moreover, SgPAP7 OE lines showed lower shoot ADP and PEP levels than the wild type, implying that SgPAP7 is involved in the catabolism and recycling of endogenous ADP and PEP, which could be beneficial for plant growth in low-Pi soils. In conclusion, SgPAP7 is a key gene with a major role in stylo adaptation to low-Pi conditions by facilitating the utilization of both exogenous and endogenous organic phosphorus sources. It may also function as a PEP phosphatase involved in a glycolytic bypass pathway that minimizes the need for adenylates and Pi. Thus, SgPAP7 could be a promising target for improving tolerance of crops to low-Pi availability.

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.

Selectivity in Enzymatic Phosphorus Recycling from Biopolymers: Isotope Effect, Reactivity Kinetics, and Molecular Docking with Fungal and Plant Phosphatases.

Among ubiquitous phosphorus (P) reserves in environmental matrices are ribonucleic acid (RNA) and polyphosphate (polyP), which are, respectively, organic and inorganic P-containing biopolymers. Relevant to P recycling from these biopolymers, much remains unknown about the kinetics and mechanisms of different acid phosphatases (APs) secreted by plants and soil microorganisms. Here we investigated RNA and polyP dephosphorylation by two common APs, a plant purple AP (PAP) from sweet potato and a fungal phytase from Aspergillus niger. Trends of δ18O values in released orthophosphate during each enzyme-catalyzed reaction in 18O-water implied a different extent of reactivity. Subsequent enzyme kinetics experiments revealed that A. niger phytase had 10-fold higher maximum rate for polyP dephosphorylation than the sweet potato PAP, whereas the sweet potato PAP dephosphorylated RNA at a 6-fold faster rate than A. niger phytase. Both enzymes had up to 3 orders of magnitude lower reactivity for RNA than for polyP. We determined a combined phosphodiesterase-monoesterase mechanism for RNA and terminal phosphatase mechanism for polyP using high-resolution mass spectrometry and 31P nuclear magnetic resonance, respectively. Molecular modeling with eight plant and fungal AP structures predicted substrate binding interactions consistent with the relative reactivity kinetics. Our findings implied a hierarchy in enzymatic P recycling from P-polymers by phosphatases from different biological origins, thereby influencing the relatively longer residence time of RNA versus polyP in environmental matrices. This research further sheds light on engineering strategies to enhance enzymatic recycling of biopolymer-derived P, in addition to advancing environmental predictions of this P recycling by plants and microorganisms.

Root acid phosphatases and rhizobacteria synergistically enhance white lupin and rice phosphorus acquisition.

The rhizosheath is a belowground area that acts as a communication hub at the root-soil interface to promote water and nutrient acquisition. Certain crops, such as white lupin (Lupinus albus), acquire large amounts of phosphorus (P), owing partially to exudation of acid phosphatases (APases). Plant growth-promoting rhizobacteria also increase soil P availability. However, potential synergistic effects of root APases and rhizosheath-associated microbiota on P acquisition require further research. In this study, we investigated the roles of root purple APases (PAPs) and plant growth-promoting rhizobacteria in rhizosheath formation and P acquisition under conditions of soil drying (SD) and P treatment (+P: soil with P fertilizer; -P: soil without fertilizer). We expressed purple acid phosphatase12 (LaPAP12) in white lupin and rice (Oryza sativa) plants and analyzed the rhizosheath-associated microbiome. Increased or heterologous LaPAP12 expression promoted APase activity and rhizosheath formation, resulting in increased P acquisition mainly under SD-P conditions. It also increased the abundance of members of the genus Bacillus in the rhizosheath-associated microbial communities of white lupin and rice. We isolated a phosphate-solubilizing, auxin-producing Bacillus megaterium strain from the rhizosheath of white lupin and used this to inoculate white lupin and rice plants. Inoculation promoted rhizosheath formation and P acquisition, especially in plants with increased LaPAP12 expression and under SD-P conditions, suggesting a functional role of the bacteria in alleviating P deficit stress via rhizosheath formation. Together, our results suggest a synergistic enhancing effect of LaPAP12 and plant growth-promoting rhizobacteria on rhizosheath formation and P acquisition under SD-P conditions.

Beneficial Bacterium Azospirillum brasilense Induces Morphological, Physiological and Molecular Adaptation to Phosphorus Deficiency in Arabidopsis.

Although most cultivated soils have high levels of total phosphorus (P), the levels of bioavailable inorganic P (Pi) are insufficient. The application of plant-growth-promoting rhizobacteria (PGPR) is an eco-friendly strategy for P utilization; however, PGPR-mediated plant responses that enhance Pi acquisition remain unexplored. Here, we investigated the effect of Azospirillum brasilense on Arabidopsis adaptation to Pi deficiency. Results showed that A. brasilense inoculation alleviated Pi-deficiency-induced growth inhibition and anthocyanin accumulation and increased the total P content in Arabidopsis plants. A comprehensive analysis of root morphology revealed that A. brasilense increased root hair density and length under Pi-limited conditions. We further demonstrated that A. brasilense enhanced the acid phosphatase activity and upregulated the expression of several Pi transporter genes, such as PHOSPHATE1 (PHO1), PHOSPHATE TRANSPORTER 1:(PHT1:1) and PHT1;4. However, A. brasilense did not enhance the growth o total P content in pht1;1, pht1;4 and pht1;1pht1;4 mutants. Moreover, A. brasilense could not increase the P content and PHT1;1 expression in the root hairless mutant rsl4rsl2, because of the occurrence of low-Pi-induced PHT1;1 and PHT1;4 in root hairs. These results indicate that A. brasilense can promote root hair development and enhance acid phosphatase activity and Pi transporter expression levels, consequently improving the Pi absorption capacity and conferring plant tolerance to Pi deficiency.

The purple acid phosphatase GmPAP17 predominantly enhances phosphorus use efficiency in soybean.

Purple acid phosphatase (PAP) is an important plant acid phosphatase, which can secrete to the rhizosphere to decompose organophosphorus, promote phosphorus use efficiency, plant growth and development. However, little is known about the functions of intracellular PAP in plants, especially for soybean. Our previous study integrating QTL mapping and transcriptome analysis identified an promising low phosphorus (LP)-induced gene GmPAP17. Here, we determined that GmPAP17 was mainly expressed in roots and had a strong response to LP stress. Furthermore, and the relative expression in the root of LP tolerant genotypes NN94-156 was significantly greater than that of LP sensitive genotype Bogao after LP stress treatment. The overexpression of GmPAP17 significantly enhanced both acid phosphatase activity and growth performance of hairy roots under LP stress condition, it was vice versa for RNAi interference of GmPAP17, indicating that GmPAP17 plays an important role in P use efficiency. Moreover, yeast two-hybrid and bimolecular fluorescence complementation analysis showed that GmRAP2.2 was involved in the regulation network of GmPAP17. Taken together, our results suggest that GmPAP17 is a novel plant PAP that functions in the adaptation of soybean to LP stress, possibly through its involvement in P recycling in plants.

Purple acid phosphatases: roles in phosphate utilization and new emerging functions.

Plants strive for phosphorus (P), which is an essential mineral for their life. Since P availability is limiting in most of the world's soils, plants have evolved with a complex network of genes and their regulatory mechanisms to cope with soil P deficiency. Among them, purple acid phosphatases (PAPs) are predominantly associated with P remobilization within the plant and acquisition from the soil by hydrolyzing organic P compounds. P in such compounds remains otherwise unavailable to plants for assimilation. PAPs are ubiquitous in plants, and similar enzymes exist in bacteria, fungi, mammals, and unicellular eukaryotes, but having some differences in their catalytic center. In the recent past, PAPs' roles have been extended to multiple plant processes like flowering, seed development, senescence, carbon metabolism, response to biotic and abiotic stresses, signaling, and root development. While new functions have been assigned to PAPs, the underlying mechanisms remained understood poorly. Here, we review the known functions of PAPs, the regulatory mechanisms, and their relevance in crop improvement for P-use-efficiency. We then discuss the mechanisms behind their functions and propose areas worthy of future research. Finally, we argue that PAPs could be a potential target for improving P utilization in crops. In turn, this is essential for sustainable agriculture.

Investigating the thermodynamic and kinetics properties of acid phosphatase extracted and purified from seedlings of Chenopodium murale.

Herein acid phosphatase isoenzyme was extracted from the C. murale seedlings. The purification was accomplished by chromatographic techniques and passing through DEAE-cellulose and Sephadex G-100 column. The specific activity of acid phosphatase 5.75 U/mg of protein was obtained with 66 purification fold 15.8% yield and molecular mass was 29 kDa with very faint bands corresponding to 18 kDa and 14 kDa. The maximal activity at pH 5.0 and 50 °C best illustrated by first order kinetics. When temperature was raised (55 °C to 75 °C), the deactivation rate constant was increased from 0.001 to 0.014 min-1, while half-life was decreased from 693 to 49 min-1. The results of activity collected at different temperature were then used to estimate, activation energy of hydrolysis reaction (Ea = 47.59 kJmol-1). A high Z-value (18.86 °C min-1) was obtained indicating a less sensitivity towards temperatures. The residual activity examinations were carried out from 55 °C to 75 °C and assessing the Deactivation Energy (Ed 116.39 kJmol-1), Enthalpy change (ΔH° 113.55kJmol-1), Entropy change (ΔS° 110.33kJmol-1) and change in Gibbs free energy (ΔG° 10.02 kJmol-1). Taken together, thermodynamic parameters confirm the high stability of enzyme and show potential commercial applicability.

Purple acid phosphatase 10c encodes a major acid phosphatase that regulates plant growth under phosphate-deficient conditions in rice.

Whilst constitutive overexpression of particular acid phosphatases (APases) can increase utilization of extracellular organic phosphate, negative effects are frequently observed in these transgenic plants under conditions of inorganic phosphate (Pi) sufficiency. In this study, we identified rice purple acid phosphatase 10c (OsPAP10c) as being a novel and major APase that exhibits activities associated both with the root surface and with secretion. Two constructs were used to generate the OsPAP10c-overexpression plants by driving its coding sequence with either a ubiquitin promoter (UP) or the OsPAP10c-native promoter (NP). Compared with the UP transgenic plants, lower expression levels and APase activities were observed in the NP plants. However, the UP and NP plants both showed a similar ability to degrade extracellular ATP and both promoted root growth. The growth performance and yield of the NP transgenic plants were better than the wild-type and UP plants in both hydroponic and field experiments irrespective of the level of Pi supply. Overexpression of APase by its native promoter therefore provides a potential way to improve crop production that might avoid increased APase activity in untargeted tissues and its inhibition of the growth of transgenic plants.

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

MAIN CONCLUSION: 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.

SapM mutation to improve the BCG vaccine: Genomic, transcriptomic and preclinical safety characterization.

The Mycobacterium bovis Bacille Calmette Guérin (BCG) vaccine shows variable efficacy in protection against adult tuberculosis (TB). Earlier, we have described a BCG mutant vaccine with a transposon insertion in the gene coding for the secreted acid phosphatase SapM, which led to enhanced long-term survival of vaccinated mice challenged with TB infection. To facilitate development of this mutation as part of a future improved live attenuated TB vaccine, we have now characterized the genome and transcriptome of this sapM::Tn mutant versus parental BCG Pasteur. Furthermore, we show that the sapM::Tn mutant had an equal low pathogenicity as WT BCG upon intravenous administration to immunocompromised SCID mice, passing this important safety test. Subsequently, we investigated the clearance of this improved vaccine strain following vaccination and found a more effective innate immune control over the sapM::Tn vaccine bacteria as compared to WT BCG. This leads to a fast contraction of IFNγ producing Th1 and Tc1 cells after sapM::Tn BCG vaccination. These findings corroborate that a live attenuated vaccine that affords improved long-term survival upon TB infection can be obtained by a mutation that further attenuates BCG. These findings suggest that an analysis of the effectiveness of innate immune control of the vaccine bacteria could be instructive also for other live attenuated TB vaccines that are currently under development, and encourage further studies of SapM mutation as a strategy in developing a more protective live attenuated TB vaccine.

Identification of Tea Plant Purple Acid Phosphatase Genes and Their Expression Responses to Excess Iron.

Purple acid phosphatase (PAP) encoding genes are a multigene family. PAPs require iron (Fe) to exert their functions that are involved in diverse biological roles including Fe homeostasis. However, the possible roles of PAPs in response to excess Fe remain unknown. In this study, we attempted to understand the regulation of PAPs by excess Fe in tea plant (Camellia sinensis). A genome-wide investigation of PAP encoding genes identified 19 CsPAP members based on the conserved motifs. The phylogenetic analysis showed that PAPs could be clustered into four groups, of which group II contained two specific cysteine-containing motifs "GGECGV" and "YERTC". To explore the expression patterns of CsPAP genes in response to excessive Fe supply, RNA-sequencing (RNA-seq) analyses were performed to compare their transcript abundances between tea plants that are grown under normal and high iron conditions, respectively. 17 members were shown to be transcribed in both roots and leaves. When supplied with a high amount of iron, the expression levels of four genes were significantly changed. Of which, CsPAP15a, CsPAP23 and CsPAP27c were shown as downregulated, while the highly expressed CsPAP10a was upregulated. Moreover, CsPAP23 was found to be alternatively spliced, suggesting its post-transcriptional regulation. The present work implicates that some CsPAP genes could be associated with the responses of tea plants to the iron regime, which may offer a new direction towards a further understanding of iron homeostasis and provide the potential approaches for crop improvement in terms of iron biofortification.

Genome-wide analysis of purple acid phosphatase (PAP) family proteins in Jatropha curcas L.

Purple acid phosphatase (PAP) family genes play a crucial role in the phosphorus (P) foraging and recycling. There are 25 putative Jatropha curcas PAP genes (JcrPAP) were identified and classified into three groups based on their molecular weights. Subcellular localization prediction indicated that most of the JcrPAPs were localized to secretory pathway. Several PAPs possess signal peptide motifs and varied numbers of N-glycosylation and transmembrane helix motifs. JcrPAP proteins have 3-5 active pocket sites comprising 1 to 11 binding residues which interact with different ligands such as iron (Fe), N-acetyl l-d-Glucosamine (NAG), zinc (Zn) and manganese (Mn). The core structure of the predicted JcrPap28 was similar to the Ipomoea batatas Pap protein. Most of the JcrPAP genes showed higher expression in the root tissues compared to stem and leaf tissues. Several JcrPAP genes were upregulated under low phosphorus conditions. JcrPAP genes such as JcrPap26b, JcrPap27b, and JcrPap28 have shown multifold induction in low phosphorus treated plants which suggest that these genes might be involved in phosphorus metabolism. The present study provided the structural variations and expression regulation of JcrPAP genes in the economically viable biodiesel crop and it would be helpful for the crop improvement under phosphorus limiting conditions.

A rational design to enhance the resistance of Escherichia coli phytase appA to trypsin.

Escherichia coli phytase appA, which hydrolyzes phytate, has been widely applied as an important feed supplement, but its resistance to trypsin needs to be improved. Six putative solvent-accessible amino acid residues (K74, K75, K180, R181, K183, and K363), which could be easily attacked by trypsin, were selected to improve trypsin tolerance of Escherichia coli phytase appA. Inspection of the three-dimensional structure and computational design via hydrogen bond analysis, six optimal mutation sites of K74D/K75Q/K180N/R181N/K183S/K363N, which strengthened the hydrogen bonding, were performed to generate three mutants. Results showed that the most beneficial mutant appA-M6 had a specific activity of 3262 U/mg with molecular weight of approximately 52-55 kDa. Similar to appA-WT, the optimal pH (4.5) and temperature (60 °C) of appA-M6 were unchanged. Compared with appA-WT, appA-M6 showed a significant enhancement (p < 0.05) in resistance to trypsin and a 3.8 °C increase in melting temperature (Tm). We concluded that introduction of hydrogen bonds and N-glycosylation modification resulted in decreased enzyme flexibility and increased the enzyme stability against proteolysis and thermal denaturation. The mutant appA-M6 generated in this study could be applied for the large-scale commercial production of phytase and thus could benefit the food and feed industry.

Acid phosphatase gene GmHAD1 linked to low phosphorus tolerance in soybean, through fine mapping.

KEY MESSAGE: Map-based cloning identified GmHAD1, a gene which encodes a HAD-like acid phosphatase, associated with soybean tolerance to low phosphorus stress. Phosphorus (P) deficiency in soils is a major limiting factor for crop growth worldwide. Plants may adapt to low phosphorus (LP) conditions via changes to root morphology, including the number, length, orientation, and branching of the principal root classes. To elucidate the genetic mechanisms for LP tolerance in soybean, quantitative trait loci (QTL) related to root morphology responses to LP were identified via hydroponic experiments. In total, we identified 14 major loci associated with these traits in a RIL population. The log-likelihood scores ranged from 2.81 to 7.43, explaining 4.23-13.98% of phenotypic variance. A major locus on chromosome 08, named qP8-2, was co-localized with an important P efficiency QTL (qPE8), containing phosphatase genes GmACP1 and GmACP2. Another major locus on chromosome 10 named qP10-2 explained 4.80-13.98% of the total phenotypic variance in root morphology. The qP10-2 contains GmHAD1, a gene which encodes an acid phosphatase. In the transgenic soybean hairy roots, GmHAD1 overexpression increased P efficiency by 8.4-16.5% relative to the control. Transgenic Arabidopsis plants had higher biomass than wild-type plants across both short- and long-term P reduction. These results suggest that GmHAD1, an acid phosphatase gene, improved the utilization of organic phosphate by soybean and Arabidopsis plants.

OsPAP26 Encodes a Major Purple Acid Phosphatase and Regulates Phosphate Remobilization in Rice.

During phosphate (Pi) starvation or leaf senescence, the accumulation of intracellular and extracellular purple acid phosphatases (PAPs) increases in plants in order to scavenge organic phosphorus (P). In this study, we demonstrated that a PAP-encoding gene in rice, OsPAP26, is constitutively expressed in all tissues. While the abundance of OsPAP26 transcript is not affected by Pi supply, it is up-regulated during leaf senescence. Furthermore, Pi deprivation and leaf senescence greatly increased the abundance of OsPAP26 protein. Overexpression or RNA interference (RNAi) of OsPAP26 in transgenic rice significantly increased or reduced APase activities, respectively, in leaves, roots and growth medium. Compared with wild-type (WT) plants, Pi concentrations of OsPAP26-overexpressing plants increased in the non-senescing leaves and decreased in the senescing leaves. The increased remobilization of Pi from the senescing leaves to non-senescing leaves in the OsPAP26-overexpressing plants resulted in better growth performance when plants were grown in Pi-depleted condition. In contrast, OsPAP26-RNAi plants retained more Pi in the senescing leaves, and were more sensitive to Pi starvation stress. OsPAP26 was found to localize to the apoplast of rice cells. Western blot analysis of protein extracts from callus growth medium confirmed that OsPAP26 is a secreted PAP. OsPAP26-overexpressing plants were capable of converting more ATP into inorganic Pi in the growth medium, which further supported the potential role of OsPAP26 in utilizing organic P in the rhizosphere. In summary, we concluded that OsPAP26 performs dual functions in plants: Pi remobilization from senescing to non-senescing leaves; and organic P utilization.

Lysosomal acid phosphatase 2 is an unfavorable prognostic factor but is associated with better survival in stage II colorectal cancer patients receiving chemotherapy.

Colorectal cancer (CRC) is one of the leading cancers worldwide. Surgery is the main therapeutic modality for stage II CRC. However, the implementation of adjuvant chemotherapy remains controversial and is not universally applied so far. In this study, we found that the protein expression of lysosomal acid phosphatase 2 (ACP2) was increased in CRC and that stage II CRC patients with high ACP2 expression showed a poorer outcome than those with low ACP2 expression (p = 0.004). To investigate this discrepancy, we analyzed the relation between ACP2 expression and several clinical cofactors.Among patients who received chemotherapy, those with an high expression of ACP2 showed better survival in both stage II and III CRC than those with low ACP2 expression. In stage II CRC patients, univariate analysis showed ACP2 expression and T stage to be cofactors significantly associated with overall survival (ACP2: p = 0.006; T stage: p = 0.034). Multivariate Cox proportion hazard model analysis also revealed ACP2 to be an independent prognostic factor for overall survival (ACP2: p = 0.006; T stage: p = 0.041). Furthermore, ACP2-knockdown CRC cells showed an increase in chemoresistance to 5-FU treatment and increased proliferation marker in the ACP2 knockdown clone.Taken together, our results suggested that ACP2 is an unfavorable prognostic factor for stage II CRC and may serve as a potential chemotherapy-sensitive marker to help identify a subset of stage II and III CRC patients for whom chemotherapy would improve survival.Highlights1. To the best of our knowledge, the study is the first report to show ACP2 overexpression in human colorectal cancer (CRC) and its association with poor outcome in stage II CRC.2. Patients with stage II and III CRCs with high expression of ACP2 were more sensitive to chemotherapy than those with a low expression.3. ACP2 expression may serve as a marker for CRC patients receiving chemotherapy and help identify the subset of CRC patients who would benefit from chemotherapy.

Improvement in phosphate acquisition and utilization by a secretory purple acid phosphatase (OsPAP21b) in rice.

Phosphate (Pi) deficiency in soil system is a limiting factor for rice growth and yield. Majority of the soil phosphorus (P) is organic in nature, not readily available for root uptake. Low Pi-inducible purple acid phosphatases (PAPs) are hypothesized to enhance the availability of Pi in soil and cellular system. However, information on molecular and physiological roles of rice PAPs is very limited. Here, we demonstrate the role of a novel rice PAP, OsPAP21b in improving plant utilization of organic-P. OsPAP21b was found to be under the transcriptional control of OsPHR2 and strictly regulated by plant Pi status at both transcript and protein levels. Biochemically, OsPAP21b showed hydrolysis of several organophosphates at acidic pH and possessed sufficient thermostability befitting for high-temperature rice ecosystems with acidic soils. Interestingly, OsPAP21b was revealed to be a secretory PAP and encodes a distinguishable major APase (acid phosphatase) isoform under low Pi in roots. Further, OsPAP21b-overexpressing transgenics showed increased biomass, APase activity and P content in both hydroponics supplemented with organic-P sources and soil containing organic manure as sole P source. Additionally, overexpression lines depicted increased root length, biomass and lateral roots under low Pi while RNAi lines showed reduced root length and biomass as compared to WT. In the light of these evidences, present study strongly proposes OsPAP21b as a useful candidate for improving Pi acquisition and utilization in rice.

The purple acid phosphatase GmPAP21 enhances internal phosphorus utilization and possibly plays a role in symbiosis with rhizobia in soybean.

Induction of secreted and intracellular purple acid phosphatases (PAPs; EC 3.1.3.2) is widely recognized as an adaptation of plants to phosphorus (P) deficiency. The secretion of PAPs plays important roles in P acquisition. However, little is known about the functions of intracellular PAP in plants and nodules. In this study, we identified a novel PAP gene GmPAP21 in soybean. Expression of GmPAP21 was induced by P limitation in nodules, roots and old leaves, and increased in roots with increasing duration of P starvation. Furthermore, the induction of GmPAP21 in nodules and roots was more intensive than in leaves in both P-efficient genotype HN89 and P-inefficient genotype HN112 in response to P starvation, and the relative expression in the leaves and nodules of HN89 was significantly greater than that of HN112 after P deficiency treatment. Further functional analyses showed that over-expressing GmPAP21 significantly enhanced both acid phosphatase activity and growth performance of hairy roots under P starvation condition, indicating that GmPAP21 plays an important role in P utilization. Moreover, GUS expression driven by GmPAP21 promoter was shown in the nodules besides roots. Overexpression of GmPAP21 in transgenic soybean significantly inhibited nodule growth, and thereby affected plant growth after inoculation with rhizobia. This suggests that GmPAP21 is also possibly involved in regulating P metabolism in nodules. Taken together, our results suggest that GmPAP21 is a novel plant PAP that functions in the adaptation of soybean to P starvation, possibly through its involvement in P recycling in plants and P metabolism in nodules.