Linking the depletion of rhizosphere phosphorus to the heterologous expression of a fungal phytase in Nicotiana tabacum as revealed by enzyme-labile P and solution 31P NMR spectroscopy

• Published in: Rhizosphere Vol. 3; pp. 82 - 91
• Main Authors: Giles, Courtney D., George, Timothy S., Brown, Lawrie K., Mezeli, Malika, Shand, Charles A., Richardson, Alan E., Mackay, Regina, Wendler, Renate, Darch, Tegan, Menezes-Blackburn, Daniel, Cooper, Pat, Stutter, Marc I., Lumsdon, David G., Blackwell, Martin S.A., Wearing, Catherine, Zhang, Hao, Haygarth, Philip M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2017
• Subjects: 31P NMR spectroscopy; agroecosystems; Aspergillus niger; biomass; exudation; fertilizer requirements; fungi; heterologous gene expression; Nicotiana tabacum; nuclear magnetic resonance spectroscopy; nutrient use efficiency; orthophosphates; phosphonates; Phosphorus; Phytase; phytases; Phytate; phytic acid; rhizosphere; soil pH; soil quality; stable isotopes; Tobacco; transgenic plants; pH; Phosphorus; Phytase; Tobacco; 31P NMR spectroscopy; Phytate
• ISSN: 2452-2198; 2452-2198
• DOI: 10.1016/j.rhisph.2016.11.004

Root exudation of phytase could improve the ability of plants to access organic forms of soil phosphorus (P), thereby minimizing fertilizer requirements and improving P use efficiency in agroecosystems. After 75 days growth in a high available P soil, shoot biomass and P accumulation, soil pH, and rhizosphere P depletion were investigated in Nicotiana tabacum wild-type and transgenic plant-lines expressing and exuding Aspergillus niger phytase (ex::phyA), or a null-vector control. Solution 31P NMR analysis revealed a 7% to 11% increase in orthophosphate and a comparable depletion of undefined monoester P compounds (-13 to -18%) in the rhizosphere of tobacco plants relative to the unplanted soil control. Wild-type plants had the greatest impact on the composition of rhizosphere P based on the depletion of other monoester P, polyphosphate, and phosphonate species. The depletion of phytase-labile P by ex::phyA plants was associated with decreased proportions of other monoester P, rather than myo-InsP6 as expected. Rhizosphere pH increased from 6.0 to 6.5-6.7 in transgenic plant soils, beyond the pH optimum for A. niger phyA activity (pH=5), and may explain the limited specificity of ex::phyA plants for phytate in this soil. The efficacy of single exudation traits (e.g., phytase) therefore appear to be limited in P-replete soil conditions and may be improved where soil pH matches the functional requirements of the enzyme or trait of interest. [Display omitted]