Improving Plant Access to Insoluble Phytate: A Combinatorial Strategy of Plant and Bacterial Solubilization and Hydrolysis Processes.

Mineral phosphorus (P) consumption and agricultural nutrient pollution could be minimized by improving crop access to native soil P. The bioavailability of phytate (IHP; <50% total soil P) is limited in soil due to precipitation and sorption reactions which are inhibitory to degradation by phytases. The role of plant and bacterial organic anion (OA) production in the solubility and bioavailability of IHP was assessed in tobacco (Nicotiana tabacum) grown on sorbed (goethite, Gt) and precipitated (calcium, Ca) P sources. Wild-type (WT) tobacco was transformed to over-express Peniophora lycii phytase (PHY) and MATE-type transporters (CIT), resulting in 33-fold higher phytase activity and 2.6-fold higher citrate in exudates, respectively. Consistent with exudate characteristics, Gt-IHP was 4-fold more available to PHY, and Gt-phosphate was 2-fold more available to CIT, relative to the other plant-lines. Wild-type and CIT plants inoculated with an OA-producing Pseudomonas sp. contained 7- and 10-fold more shoot P, respectively, than plants grown in sterile media. The PHY plant-line was not influenced by the inoculum, likely due to direct hydrolysis of CaIHP by exogenous phytases. The combination of solubilization and hydrolysis services provided by Pseudomonas improves plant utilization of insoluble IHP, and is therefore a suitable target for further optimization of crop P utilization efficiency.