Molecular characterization and functional analysis of OsPHY2, a phytase gene classified in histidine acid phosphatase type in rice (Oryza sativa L.)

Abstract

Phytic acid (PA) and its derivatives contain the major portion of phosphorus in the cereal seed and chelates divalent cations. During germination, both minerals and phosphate are released upon phytase-catalyzed degradation of PA. In this study, a phytase gene classified into histidine acid phosphatase type in rice referred to OsPHY2 was characterized. OsPHY2 is 2060 bp in length, encoding a polypeptide of 519 amino acids. OsPHY2 contains HP_HAP_like domain, a 24-aa signal peptide at the N-terminal and was targeted to the cytoplasm membrane after ER sorted. Phylogenetic analysis suggests that OsPHY2 shares high similarity to the phytase genes in wheat and a subset of genes without characterized functions in other plant species. During the seed germination, the transcripts of OsPHY2 were much more detected in the germinated seeds than in the primary roots and the leaves. Prokaryotic expressed OsPHY2 has a strong function on degradation of phytate, with optimal temperature of 47°C and optimal pH of 3.5. Under the guidance of patatin signal peptide (PSP) of potato, the OsPHY2 expressed in tobacco could be secreted by the rhizosphere and hydrolyze the phytate into Pi, leading to a significantly more inorganic phosphate (Pi) accumulated and growth improved in plants under the condition using phytate as the sole phosphorus source. Therefore, as one HAP type of the phytase genes, OsPHY2 plays a critical role on the degradation of the phytins during the seed germination and has a potential application on the generation of elite crop germplasms with high use of efficiency of phytate and a large quantity of organic phosphate compounds in the arable land.

Key words: Rice (Oryza sativa L.), phytase gene, expression, biochemical property, transgene analysis.