In plants, phosphate (Pi) homeostasis is regulated by the interaction of PHR transcription factors with stand-alone SPX proteins, which act as sensors for inositol pyrophosphates. Here, we combined different methods t...
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In plants, phosphate (Pi) homeostasis is regulated by the interaction of PHR transcription factors with stand-alone SPX proteins, which act as sensors for inositol pyrophosphates. Here, we combined different methods to obtain a comprehensive picture of how inositol (pyro)phosphate metabolism is regulated by Pi and dependent on the inositol phosphate kinase ITPk1. We found that inositol pyrophosphates are more responsive to Pi than lower inositol phosphates, a response conserved across kingdoms. With CE-ESI-MS we could separate different InsP7 isomers in Arabidopsis and rice, and identify 4/6-InsP7 and a PP-InsP4 isomer hitherto not reported in plants. We found that the inositol pyrophosphates 1/3-InsP7, 5-InsP7 and InsP8 increase severalfold in shoots after Pi resupply and that tissue-specific accumulation of inositol pyrophosphates relies on ITPk1 activities and MRP5-dependent InsP6 compartmentalization. Notably, ITPk1 is critical for Pi-dependent 5-InsP7 and InsP8 synthesis in planta and its activity regulates Pi starvation responses in a PHR-dependent manner. Furthermore, we demonstrate that ITPk1-mediated conversion of InsP6 to 5-InsP7 requires high ATP concentrations and that Arabidopsis ITPk1 has an ADP phosphotransferase activity to dephosphorylate specifically 5-InsP7 under low ATP. Collectively, our study provides deeper insights into Pi-dependent changes in nutritional and energetic states with the synthesis of regulatory inositol pyrophosphates.
(Molecular Plant 14,1864-1880;November 12021)We identified a mistake made when calculating the absolute concentrations of inositol(pyro)phosphates derived from CE-ESl-MS measurements reported in the originally publish...
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(Molecular Plant 14,1864-1880;November 12021)We identified a mistake made when calculating the absolute concentrations of inositol(pyro)phosphates derived from CE-ESl-MS measurements reported in the originally published version of our *** to a calculation error when determining concentrations per fresh biomass,the absolute values shown in the manuscript are approximately 30-fold lower than they should *** mistake affects Figures 2D,3C,4C,and 7D and Figures S4,S11B,S13,and *** all conclusions made in the article referred to relative differences between genotypes and treatments,they remained unaffected by these mistakes.
Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter....
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Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter. Soils with high micro-bial activity may experience N immobilization (or reduced net N mineralization), and this issue remains unresolved in how to predict these conditions of net mineralization or net immobilization. Prediction may become possible with the use of a more sensitive method to determine soil C:N ratios stemming from the water-extractable C and N pools that can be readily adapted by both commercial and university soil testing labs. Soil microbial activity is highly related to soil organic C and N, as well as to water-extractable organic C (WEOC) and water-extractable organic N (WEON). The relationship between soil respiration and WEOC and WEON is stronger than between respiration and soil organic C (SOC) and total organic N (TON). We explored the relationship between soil organic C:N and water-extractable organic C:N, as well as their relationship to soil microbial activity as measured by the flush of CO2 following rewetting of dried soil. In 50 different soils, the relationship between soil microbial activity and water-extractable organic C:N was much stronger than for soil organic C: N. We concluded that the water-extractable organic C:N was a more sensitive measurement of the soil substrate which drives soil microbial activity. We also suggest that a water-extractable organic C:N level > 20 be used as a practical threshold to separate those soils that may have immobilized N with high microbial activity.
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