acid-phosphatase and ethylene

Induction and secretion of acid phosphatases (APases) is an adaptive response that plants use to cope with P (Pi) deficiency in their environment. The molecular mechanism that regulates this response, however, is poorly understood. In this work, we identified an Arabidopsis (Arabidopsis thaliana) mutant, hps8, which exhibits enhanced APase activity on its root surface (also called root-associated APase activity). Our molecular and genetic analyses indicate that this altered Pi response results from a mutation in the AtTHO1 gene that encodes a subunit of the THO/TREX protein complex. The mutation in another subunit of this complex, AtTHO3, also enhances root-associated APase activity under Pi starvation. In Arabidopsis, the THO/TREX complex functions in mRNA export and miRNA biogenesis. When treated with Ag(+), an inhibitor of ethylene perception, the enhanced root-associated APase activity in hps8 is largely reversed. hpr1-5 is another mutant allele of AtTHO1 and shows similar phenotypes as hps8 ein2 is completely insensitive to ethylene. In the hpr1-5ein2 double mutant, the enhanced root-associated APase activity is also greatly suppressed. These results indicate that the THO/TREX complex in Arabidopsis negatively regulates root-associated APase activity induced by Pi starvation by inhibiting ethylene signaling. In addition, we found that the miRNA399-PHO2 pathway is also involved in the regulation of root-associated APase activity induced by Pi starvation. These results provide insight into the molecular mechanism underlying the adaptive response of plants to Pi starvation.

Topics: Acid Phosphatase; Arabidopsis; Arabidopsis Proteins; Cell Nucleus; Ethylenes; Gene Expression Profiling; Gene Expression Regulation, Plant; MicroRNAs; Multiprotein Complexes; Mutation; Phenotype; Phosphates; Plant Roots; Protein Subunits; Real-Time Polymerase Chain Reaction; Signal Transduction

The induction and secretion of acid phosphatases (APases) is a universal response of plants to phosphate (Pi) starvation. AtPAP10 (Arabidopsis purple acid phosphatase 10) is a major Pi starvation-induced APase that is associated with the root surface in Arabidopsis. So far, the roles of local and systemic signalling in regulating root-associated AtPAP10 activity remain largely unknown. In this work, we show that a decrease of local, external Pi availability is sufficient to induce AtPAP10 transcription in roots in the presence of sucrose, a systemic signal from shoots, whereas the magnitude of the induction is affected by the Pi status of the whole plant. Once the AtPAP10 mRNAs are synthesized in roots, subsequent accumulation of AtPAP10 proteins in root cells and increase in AtPAP10 activity on the root surface are mainly controlled by local signalling. Previously, ethylene has been demonstrated to be a positive regulator of AtPAP10 activity. In this study, we provide evidence that under Pi deficiency ethylene mainly modulates enzymatic activity of AtPAP10 on the root surface, but not AtPAP10 transcription and protein accumulation, suggesting that it functions as a local signal. Furthermore, our work indicates that the effect of ethylene on the induction of root-associated AtPAP10 activity depends on sucrose, but that the effect of sucrose does not depend on ethylene. These results reveal new insights into the distinct roles of local and systemic signalling in the regulation of root-associated AtPAP10 activity under Pi starvation.

Topics: Acid Phosphatase; Arabidopsis; Arabidopsis Proteins; Ethylenes; Gene Expression Regulation, Plant; Genes, Plant; Models, Biological; Mutation; Phosphates; Plant Roots; RNA, Messenger; Signal Transduction; Sucrose; Transcription, Genetic

The phytohormone ethylene plays important roles in regulating plant responses to phosphate (Pi) starvation. To date, however, no molecular components have been identified that interact with ethylene signalling in regulating such responses. In this work, an Arabidopsis mutant, hps4, was characterized that exhibits enhanced responses to Pi starvation, including increased inhibition of primary root growth, enhanced expression of Pi starvation-induced genes, and overproduction of root-associated acid phosphatases. Molecular cloning indicated that hps4 is a new allele of SABRE, which was previously identified as an important regulator of cell expansion in Arabidopsis. HPS4/SABRE antagonistically interacts with ethylene signalling to regulate plant responses to Pi starvation. Furthermore, it is shown that Pi-starved hps4 mutants accumulate more auxin in their root tips than the wild type, which may explain the increased inhibition of their primary root growth when grown under Pi deficiency.

Topics: Acid Phosphatase; Alleles; Anthocyanins; Arabidopsis; Arabidopsis Proteins; Chromosome Mapping; Ethylenes; Gene Expression Regulation, Plant; Indoleacetic Acids; Intracellular Signaling Peptides and Proteins; Meristem; Mutation; Organ Specificity; Phosphates; Plant Growth Regulators; Plant Leaves; Plant Roots; Signal Transduction; Stress, Physiological

When plants are subjected to a deficiency in inorganic phosphate (Pi), they exhibit an array of responses to cope with this nutritional stress. In this work, we have characterized two Arabidopsis mutants, hps3-1 and hps3-2 (hypersensitive to Pi starvation 3), that have altered expression of Pi starvation-induced (PSI) genes and enhanced production of acid phosphatase (APase) when grown under either Pi sufficiency or deficiency conditions. hps3-1 and hps3-2, however, accumulate less anthocyanin than the wild type when grown on a Pi-deficient medium. Molecular cloning indicated that the phenotypes of hps3 mutants were caused by mutations within the ETO1 (ETHYLENE OVERPRODUCTION 1) gene. In Arabidopsis, ETO1 encodes a negative regulator of ethylene biosynthesis, and mutation of ETO1 causes Arabidopsis seedlings to overproduce ethylene. The ethylene biosynthesis inhibitor aminoethoxyvinyl glycine or the ethylene perception inhibitor Ag(+) suppressed all the mutant phenotypes of hps3. Taken together, these results provide further genetic evidence that ethylene is an important regulator of multiple plant responses to Pi starvation. Furthermore, we found that a change in ethylene level has differential effects on the expression of PSI genes, maintenance of Pi homeostasis, production of APase and accumulation of anthocyanin. We also demonstrated that ethylene signaling mainly regulates the activity of root surface-associated APases rather than total APase activity.

Topics: Acid Phosphatase; Anthocyanins; Arabidopsis; Arabidopsis Proteins; Chromosome Mapping; Cloning, Molecular; Culture Media; Enzyme Induction; Ethylenes; Gene Expression Regulation, Plant; Genes, Plant; Glycine; Homeostasis; Mutagenesis, Insertional; Mutation; Phenotype; Phosphates; Plant Roots; Seedlings; Signal Transduction

• With the exception of root hair development, the role of the phytohormone ethylene is not clear in other aspects of plant responses to inorganic phosphate (Pi) starvation. • The induction of AtPT2 was used as a marker to find novel signalling components involved in plant responses to Pi starvation. Using genetic and chemical approaches, we examined the role of ethylene in the regulation of plant responses to Pi starvation. • hps2, an Arabidopsis mutant with enhanced sensitivity to Pi starvation, was identified and found to be a new allele of CTR1 that is a key negative regulator of ethylene responses. 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, increases plant sensitivity to Pi starvation, whereas the ethylene perception inhibitor Ag+ suppresses this response. The Pi starvation-induced gene expression and acid phosphatase activity are also enhanced in the hps2 mutant, but suppressed in the ethylene-insensitive mutant ein2-5. By contrast, we found that ethylene signalling plays a negative role in Pi starvation-induced anthocyanin production. • These findings extend the roles of ethylene in the regulation of plant responses to Pi starvation and will help us to gain a better understanding of the molecular mechanism underlying these responses.

Topics: Acid Phosphatase; Alleles; Amino Acids, Cyclic; Anthocyanins; Arabidopsis; Arabidopsis Proteins; Ethylenes; Gene Expression Regulation, Plant; Genes, Plant; Models, Biological; Mutation; Phosphate Transport Proteins; Phosphates; Protein Kinases; Signal Transduction