Plant Physiol, August 2001, Vol. 126, pp. 1598-1608
A Novel Phytase with Sequence Similarity to Purple Acid
Phosphatases Is Expressed in Cotyledons of Germinating Soybean
Seedlings 1
Carla E.
Hegeman2 and
Elizabeth A.
Grabau*
Department of Plant Pathology, Physiology, and Weed Science, Fralin
Biotechnology Center, Virginia Tech, Blacksburg, Virginia
24061-0346
Phytic acid (myo-inositol
hexakisphosphate) is the major storage form of
phosphorus in plant seeds. During germination, stored reserves are used
as a source of nutrients by the plant seedling. Phytic acid is degraded
by the activity of phytases to yield inositol and free phosphate. Due
to the lack of phytases in the non-ruminant digestive tract,
monogastric animals cannot utilize dietary phytic acid and it is
excreted into manure. High phytic acid content in manure results in
elevated phosphorus levels in soil and water and accompanying
environmental concerns. The use of phytases to degrade seed phytic acid
has potential for reducing the negative environmental impact of
livestock production. A phytase was purified to
electrophoretic homogeneity from cotyledons of germinated soybeans (Glycine max L. Merr.). Peptide sequence data generated
from the purified enzyme facilitated the cloning of the phytase
sequence (GmPhy) employing a polymerase chain reaction
strategy. The introduction of GmPhy into soybean tissue
culture resulted in increased phytase activity in transformed cells,
which confirmed the identity of the phytase gene. It is surprising that
the soybean phytase was unrelated to previously characterized microbial
or maize (Zea mays) phytases, which were classified as
histidine acid phosphatases. The soybean phytase sequence exhibited a
high degree of similarity to purple acid phosphatases, a class of metallophosphoesterases.
1
This work was supported in part by the U.S.
Department of Agriculture National Research Initiative Competitive
Grants Program.
2
Present address: Department of Molecular Biology and
Genetics, Cornell University, Ithaca, NY 14853.
*
Corresponding author; e-mail egrabau{at}vt.edu; fax 540-231-7126.
© 2001 American Society of Plant Physiologists
