Root-specific and phosphate-regulated expression of phytase under the control of a phosphate transporter promoter enables Arabidopsis to grow on phytate as a sole P source

The efficient use of transgenic technology for the improvement of phosphorus (P) nutrition in crop plants may require the expression of introduced genes only under conditions of phosphate deficiency and only in specific tissues. We have investigated the use of the promoter from the Arabidopsis Pht1;2 phosphate transporter to drive the expression of a secretable Aspergillus niger phytase gene only in the root epidermis of phosphate-deprived plants. Deletion analysis of this promoter indicated that, while the 933 bp upstream of the start codon is sufficient for root-specific and phosphate-responsive reporter gene expression, the 2000 bp upstream of the start codon are required for maximum expression levels. We show that transgenic Arabidopsis plants in which this 2000 bp promoter drives the Aspergillus phytase gene secrete phytase enzyme only from roots when grown on medium containing low phosphate concentrations, and that this transgene enables the plants to grow on medium containing phytate as a sole P source. The growth rates and shoot P concentrations of these plants were similar when grown on phytate or phosphate as the P source, and were similar to transgenic lines in which the phytase was driven by the constitutive CaMV 35S promoter. Our results demonstrate the potential usefulness of the promoter from the Pht1;2 phosphate transporter for driving genes that may improve crop P uptake and nutrition. (C) 2003 Elsevier Ireland Ltd. All rights reserved.