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A phytase gene (phyA), isolated from Aspergillus ficuum (AF537344), was introduced into cotton (Gossypium hirsutum L.) by Agrobacteriummediated transformation to increase the phosphorus (P) acquisition efficiency of cotton. Southern and Northern blot analyses showed that the phyA was successfully incorporated into the cotton genome and expressed in transgenic lines. After growing for 45 days with phytate (Po) as the only P source, the shoot and root dry weights of the transgenic plants all increased by nearly 2.0-fold relative to those of wildtype plants, but were similar to those of transgenic plants supplied with inorganic phosphorus. The phytase activities of root extracts prepared from transgenic plants were 2.4-to 3.6-fold higher than those from wild-type plants, and the extracellular phytase activities of transgenic plants were also 4.2-to 6.3-fold higher. Furthermore, the expressed phytase was secreted into the rhizospheres as demonstrated by enzyme activity staining. The transgenic plants accumulated much higher contents of total P (up to 2.1-fold after 30 days of growth) than the wildtype plants when supplied with Po. These findings clearly showed that cotton plant transformed with a fungal phytase gene was able to secret the enzyme from the root, which markedly improved the plant's ability to utilize P from phytate. This may serve as a promising step toward the development of new cotton cultivars with improved phosphorus acquisition.

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