Physiological Functional Identification Of Rice Phosphate Transporter OsPT4

The genome sequencing of rice (Oryza sativa), a model plant of monocotyledon, has been finished. Rice functional genomics has become one of the research focuses in plant biology. In the rice genome, a total of 13 sequences can be identified as belonging to phosphate transporter (Phtl) family. Understanding of the physiological functions of phosphate transporters is essential for dissecting the molecular mechanism of phosphate uptake, translocation and utilization by plants.In our previous experiments, we observed that rice phosphate transporter genes in Phtl family. In the present study, two of the rice cultivars belong to the subspecies of Japonica, Nipponbare and Wuyu-7, were chosen for over-expression of OsPT4 through the technique of over-expression. The over-expression of target gene, mRNA expression of some Phtl family members, dry weight, total phosphate uptake, phosphate uptake, root configuration in the over-expression of T1 generation were measured in comparison to the wild type to explore the functions of OsPT4 gene on phosphate absorption and transportation in normal P suply and low P suply conditions.The main results obtained were as follows:1. The mRNA expression of OsPT4 was effectively over-expressed by transformation of the targeted gene with over-expression vector construction basing on pS1a-4 vector. 4-Ov-6 and 4-Ov-7 were chosen for further research in Nipponbare; 4-Ov-1 and 4-Ov-2 were chosen for further research in Wuyu-7.2. In Nipponbare, the over-expression of OsPT4 also affected the expression of other Phtl family members (OsPT1, OsPT8, OsPT12) in the rice. In the transgenic line 4-Ov-6, the expression of OsPT1 and OsPT12 relative their expression in the wild type were down regulated, and OsPT8 was faintly regulated in the roots; meanwhile, OsPT1 was up regulated, and OsPT8 and OsPT12 were faintly regulated in the shoot.In Wuyu-7, the over-expression of OsPT4 also affected the expression of other Phtl family members (OsPT1, OsPT8, OsPT12) in the rice. In the transgenic line 4-Ov-1, the expression of OsPT1 and OsPT12 relative their expression in the wild type were up regulated, and OsPT8 was faintly regulated in the roots; meanwhile, OsPT8 and OsPT12 were up regulated, and OsPT10 was faintly up regulated in the shoot.The regulated expression of some other Pi transporters by over-expression of OsPT4, there was a possible functional interaction among OsPT4 and other members of Phtl family.3. Over-expression of OsPT4 increased some parts of the following:dry weight, total root length, total root surface area, root volume and root tips number.In Nipponbare, dry weight of the transgenic lines 4-Ov-6 and 4-Ov-7 increase faintly under P-deficiency. Under normal P-supply, total root length, total root surface area, root volume and root tips number indicate no significant difference at 5% level; under P-deficiency, total root surface area and root tips number indicate significant difference at 5% level, but total root length and root volume indicate no significant difference at 5% level.In Wuyu-7, dry weight of the transgenic lines 4-Ov-1 and 4-Ov-2 increase faintly under P-deficiency. Under normal P-supply, total root length and root tips number indicate significant difference at 5% level, but total root surface area and root volume indicate no significant difference at 5% level; under P-deficiency, total root length of 4-Ov-1 indicate significant difference at 5% level, but total root surface area, root volume and root tips number indicate no significant difference at 5% level.4. Under normal P-supply condition, total phosphate absorption in the transgenic lines 4-Ov-6 and 4-Ov-7 increase 10-20% in the roots and 36-50% in the shoots on average, respectively; Under low P-supply condition, transgenic lines 4-Ov-6 and 4-Ov-7 increase 8-15% in the roots and 15-30% in the shoots on average, respectively.Under normal P-supply condition, total phosphate absorption in the transgenic lines 4-Ov-1 and 4-Ov-2 increase 10-20% in the roots and 40-60% in the shoots on average, respectively; Under low P-supply condition, transgenic lines 4-Ov-1 and 4-Ov-2 increase 10-20% in the roots and 10-25% in the shoots on average, respectively.Under normal P-supply condition, Pi absorption in the transgenic lines 4-Ov-6 and 4-Ov-7 increase 10-20% in the roots and 10-20% in the shoots on average, respectively;Under low P-supply condition, transgenic lines 4-Ov-6 and 4-Ov-7 increase 8-15% in the roots and 7-20% in the shoots on average, respectively.Under normal P-supply condition, Pi absorption in the transgenic lines 4-Ov-1 and 4-Ov-2 increase 20-40% in the roots and 10-40% in the shoots on average, respectively; Under low P-supply condition, transgenic lines 4-Ov-1 and 4-Ov-2 increase 5-10% in the roots and 5-10% in the shoots on average, respectively.