Characterization of the promoter of phosphate transporter TaPHT1.2 differentially expressed in wheat varieties

TaPHT1.2 is a functional, root predominantly expressed and low phosphate (Pi) inducible high-affinity Pi transporter in wheat, which is more abundant in the roots of P-efficient wheat genotypes (e.g., Xiaoyan 54) than in P-inefficient genotypes (e.g., Jing 411) under both Pi-deficient and Pi-sufficient conditions. To characterize TaPHT1.2 further, we genetically mapped a TaPHT1.2 transporter, TaPHT1.2-D1, on the long arm of chromosome 4D using a recombinant inbred line population derived from Xiaoyan 54 and Jing 411, and isolated a1,302 bp fragment of the TaPHT1.2-D1 promoter (PrTaPHT1.2-D1) from Xiaoyan 54. TaPHT1.2-D1 shows collinearity with OsPHT1.2 that has previously been reported to mediate the translocation of Pi from roots to shoots. PrTaPHT1.2-D contains a number of Pi-starvation responsive elements, including P1BS, WRKY-binding W-box, and helix-loop-helix-binding elements. PrTaPHT1.2-D1 was then used to drive expression of beta-glucuronidase (GUS) reporter gene in Arabidopsis through Agrobacterium-mediated transformation. Histochemical analysis of transgenic Arabidopsis plants showed that the reporter gene was specifically induced by Pi-starvation and predominantly expressed in the roots. As there is only one SNP between the TaPHT1.2-D1 promoters of Xiaoyan 54 and Jing 411, and this SNP does not exist within the Pi-starvation responsive elements, the differential expression of TaPHT1.2 in Xiaoyan 54 and Jing 411 may not be caused by this SNP.