Putative phosphate transporters have been identified in a barley (Hordeum vulgare L.) genomic library by their homology to known phosphate transporters from dicot species. The genes designated HORvu;Pht1;1 and HORvu;Pht1;6 encode proteins of 521 and 535 amino acids respectively with 12 predicted membrane-spanning domains and other motifs common to the Phtl family of phosphate transporters. HORvu;Pht1;1 is expressed exclusively in roots and is strongly induced by phosphate deprivation. HORvu;Pht1;6 is expressed in the aerial parts of the plant with strongest expression in old leaves and flag leaves. In situ hybridization showed that HORvu;Pht1;6 is expressed in the phloem of vascular bundles in leaves and ears. In order to study the biochemical properties of HORvu;Pht1;1 and HORvu;Pht1;6, the genes were expressed in transgenic rice (Oryza sativa L.) plants under the control of the rice actin promoter and suspension cell cultures were generated. Cells derived from transgenic plants were able to take up phosphate at a much higher rate than control cells, demonstrating that both genes encode functional phosphate transporters. The estimated Km for phosphate for cells expressing HORvu;Pht1;1 was 9.06 +/- 0.82 microM, which is characteristic of a high-affinity transporter. The rate of phosphate uptake decreased with increasing pH, suggesting that HORvu;Pht1;1 operates as a H+/H2PO4(-) symporter. In contrast, the estimated Km for phosphate for cells expressing HORvu;Pht1;6 was 385 +/- 61 microM, which is characteristic of a low-affinity transporter. Taken together, the results suggest that HORvu;Pht1;1 functions in uptake of phosphate at the root surface, while HORvu;Pht1;6 probably functions in remobilization of stored phosphate from leaves.
Sugarcane is an important crop in tropical regions of the world, producing a very large biomass and accumulating large amounts of sucrose in the stem. In this study, we present the first report of transcript profiling using the GeneChip Sugarcane Genome Array. We have identified transcripts that are differentially expressed in the sugarcane stem during development by expression profiling using the array and total RNA derived from three disparate stem tissues (meristem, internodes 1-3, 8, and 20) from four replicates of the sugarcane variety Q117 grown in the field. We have identified 119 transcripts that were highly differentially expressed with development and have characterised members of the cellulose synthase (CesA) and cellulose synthase-like (Csl) gene families, which displayed coordinated expression during stem development. In addition, we determined that many other transcripts involved in cell wall metabolism and lignification were also co-expressed with members of the CesA and Csl gene families, offering additional insights into the dynamics of primary and secondary cell wall synthesis in the developing sugarcane stem.
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