Expression Profiling Of OsSPX Family In Rice (Oryza Sativa L.)

The SPX domain proteins identified in yeast (Saccharomyces cerevisiae) involve in phosphate transport, sensing and sorting proteins to endomembranes. The Oryza sativa genome contains at least 6 uncharacterized encoding proteins with a SPX domain at the N-terminal portion. Reverse transcription-PCR (RT-PCR) revealed the overlapping but distinct expression patterns of these OsSPX genes in leaves, roots, stems and spikelets. Histochemical analysis of promoter-driven GUS in transgenic rice for these OsSPX homologs showed a predominant activity in the vascular tissues of coleoptile, root, leave and stem. GUS activity of several OsSPXs promoter was detected in nonvascular tissues, including root cortical/epidermal cells, and pollen grains. The expression of 3 members of OsSPXs was significantly induced in root by phosphate starvation, which was further confirmed by RT-PCR analysis. The diverse expression patterns of OsSPX homologs suggest that the divergent roles of the OsSPX gene family in different development stages and in plant responses to external signal, especially in lateral root development and phosphate absorption and/or translocation underlying plant adaptation to phosphate starvation. Transient assay by bombardment of onion epidermal cells and by PEG mediated gene transter to rice protoplast showed that OsSPX: :GFP fusion proteins are located at different subcellular partitions, implying the different functional mechanisms for different family members.