磷是植物生長發育所需的必要元素，磷的含量會嚴重影響作物的產量。水稻為世界上重要的糧食作物之一，為了開發出能夠耐低磷或能高效率使用磷的水稻以因應未來磷礦不足的情況，本篇論文利用microarray 分析缺磷誘導基因的結果中，挑選出六個與缺磷相關的基因OsPSU1，OsPSU2，OsPSU3，OsPSU4，OsPSU5和OsPSU6 (Phosphate starvation up-regulated genes)，探討它們是否參與水稻缺磷反應機制。RT-PCR的分析中，顯示所選之6個OsPSUs均為缺磷誘導表現基因。與野生型水稻(WT)相比，過量表達OsPSUs轉殖水稻小苗葉片累積較多的磷，所以OsPSUs過量表達轉殖稻在磷濃度323 μM以下培養時，生長都比WT來的佳，但磷濃度1618 μM以上培養時，則是呈現比WT更嚴重的磷毒性外表型。過量表達OsPSUs轉殖水稻中，參與磷調控機制中的重要調控因子基因OsPHR2和OsPHO2表現量會大量增加，而且OsPHR2下游一個低親和力的phosphate transporter基因OsPT2的表現亦會增加。這些結果顯示，過量表現OsPSUs能提高缺磷的訊號，進而增加OsPT2的表現，增強了水稻對磷的吸收率與累積，而高磷訊號隨即提高OsPHO2的表現，負回饋抑制磷的吸收率與累積。;Phosphorus is an essential macronutrient for plant development and affects crops productivity seriously. Rice is one of major food crop in the world. The goal of this study, 6 inorganic phosphate (Pi) starvation relative genes (OsPSUs) that were identified by microarray analysis of RNA isolated from Pi-starved rice roots of seedling were investigated for rice response to phosphate starvation. Ectopic expression of each OsPSU transgenic rice lines were generated. Pi levels were higher in leaves of each transgenic line than wild-type plants cultured under normal phosphate concentration. Seedlings of transgenic lines overexpressing OsPSUs grown below in 323 μM Pi exhibit heather phenotype than wild-type. Moreover, each OsPSU transgenic lines displayed more severe Pi toxicity than wild type when they were grown in Pi concentration higher than 1618 μM. Furthermore, overexpression of each OsPSU enhanced the expression of OsPHR2 and OsPHO2, both are involved in Pi utilization pathway. In addition, expression of OsPT2, which encodes a low-affinity phosphate transporter, was also increased in each OsPSU overexpressing lines. These results suggest that all of OsPSUs enhance the rate of phosphate uptake through OsPHR2-OsPT2-mediated pathway.
