Ectopic expression of a phytase gene from Medicago truncatula Barrel Medic enhances phosphorus absorption in plants

In the present study, the phosphorus-absorption capacity of transgenic Arabidopsis plants ectopically expressing a novel phytase gene from Medicago truncatula Barrel Medic was evaluated. A full-length cDNA encoding an extracellular form of phytase was isolated from the model legume M. truncatula. The phytase gene (MtPHY1) has an open reading frame of 1 632 bp predicted to encode 543 amino acids, including an N-terminal signal peptide of 27 amino acids. The genomic sequence of the MtPHY1 gene is 5 151 bp, containing seven exons interrupted by six introns. Under high-Pi (2 mmol/L) growth conditions, higher levels of MtPHY1 transcripts accumulated in the leaf and stem than in the root. The transcript level was reduced in the stem and increased in the root, with no obvious changes in the hybridization signal detected in the leaf under low-Pi (10 mu mol/L) conditions. Chimeric transgenes were constructed by placing MtPHY1 under the control of the constitutive CaMV35S promoter and the root-specific MtPT1 promoter. Phytase activities in root apoplast of transgenic Arabidopsis were 12.3- to 16.2-fold of that in control plants. The phytase expressed was secreted into the rhizosphere, as demonstrated by HPLC analysis of phytate degradation by root exudates. Ectopic expression of MtPHY1 in Arabidopsis, leading to significant improvement in organic phosphorus absorption and plant growth, indicated that MtPHY1 has great potential for improving plant phosphorus absorption and phytoremediation.