Chromosome localization and regulation role in phosphorous uptake of phosphate transporter gene TaPht1; 4 under Pi deprivation in wheat

【Objectives】The acquisition of inorganic phosphate (Pi) and the Pi translocation across the organs and tissues in plants is mediated by phosphate transporters (PTs) located at the cytoplasmic membranes. The PTs with high-affinity property play critical roles in mediating the Pi absorption by plants under the Pi-limited condition. Currently, the molecular characterization and biological functions of PTs in wheat were few reported. In this study, using Chinese spring (CS) and its ditelosimic lines of B chromosome as materials, the localization on chromosome as well as expression patterns of TaPht1; 4, a highaffinity PT gene in wheat, was systematically studied under sufficient- and deficient-Pi conditions. In addition, the relationship between the expression levels of TaPht1; 4 and the plant phosphorus use efficiencies across various wheat cultivars under supply of lower phosphorous was determined to provide molecular basis for evaluation of phosphorus use efficiency across wheat cultivars and guidance on genetic improvement for high phosphorus usage in wheat.【Methods】The hydroponic culture method was used to cultivate seedlings of Chinese spring (CS) and its ditelosimic lines of B chromosome. The roots and leaves of all tested materials were separately harvested at three-leaf growth stage and subjected to extraction of genome DNA. PCR analysis was performed using the gene specific primers of TaPht1; 4 to identify the chromosome location of TaPht1; 4. The roots and leaves of all tested materials under conditions of sufficient- and deficient-Pi by treated with 24 h low-Pi stress were sampled and subjected to expression analysis of TaPht1; 4 gene by semiquantitative RT-PCR and real-time PCR. Using the similar methods of seedling culture, treatments of sufficient- and deficient-Pi, and gene expression analysis approaches, the parameters of phosphorus use efficiency and the expression patterns of TaPht1; 4 in wheat cultivars were investigated.【Results】 1) In contrast to CS and other its ditelosimic lines of B chromosome, TaPht1; 4 was not amplified by PCR in 3BS. Moreover, the expression analysis of TaPht1; 4 by semiquantitative RT-PCR and real-time PCR revealed that CS and all ditelosimic lines of B chromosome both in the roots and leaves under the condition of sufficient- Pi did not exhibit the expression of TaPht1; 4, and similar result was shown in the leaves under the condition of deficient-Pi. However, the transcripts of TaPht1; 4 were detected in the roots of CS as well as in the ditelosimic lines, and was not detected in that of 3BS. Therefore, TaPht1; 4 is located at the long arm of 3B and exhibits expression patterns of induction by low-Pi stress, and has root-specific expression. 2)Under the condition of sufficient-Pi, no variations on plant dry mass was observed between the 3BS and CS. By contrast, the plant dry mass of 3BS was significantly lower than that of CS under the condition of deficient-Pi. These results indicate that the plant dry matter production is largely affected by TaPht1; 4 and the long arm of 3B that situates in the TaPht1; 4. Deletion of TaPht1; 4 by missing this chromosome arm can result in significant reduction in plant dry mass under deprivation of Pi. 3)Investigations on the expression levels of TaPht1; 4，the plant dry mass, total phosphorus contents, accumulative phosphorus amount per plant, and phosphorus use efficiencies in six wheat cultivars with contrasting Pi acquisition capacity indicated that the expression levels of TaPht1; 4 was positively correlated with the Pi acquisition capacities and phosphorus use efficiencies under the condition of deficient-Pi.【Conclusions】The wheat high affinity PT gene, TaPht1; 4 is located at the long arm of 3B. Under the condition of deficient-Pi, the plant dry mass and accumulative amounts of phosphorus per plant of 3BS were significantly lower than those of CS. The expression levels of TaPht1; 4 across the wheat cultivars with contrasting Pi acquisition capacity were closely associated with their plant dry masses and accumulative amounts of phosphorus per plant under conditions of sufficient- and deficient-Pi. Taken together, TaPht1; 4 plays critical roles in regulating plant Pi acquisition in wheat under low-Pi stress, and can act as one of valuable molecular criteria in evaluating the capacity to tolerate low-Pi stress in wheat.