| Arbuscular mycorrhizal symbiosis is mutually beneficial symbiosis formed by plant roots and arbuscularmycorrhiza(AM fungi). Most of the bundle sheath plants can form a symbiotic relationship with AM fungi, which have a significant impact on plant nutrient uptake and ecological functions. Nutrition switching is the main function of the AM symbiosis. AM fungi get carbon from the plant host, while they also can provide host plants of phosphorus and nitrogen, and the promotion of plant uptake and utilization of mineral elements. In AM symbiotic system, inorganic phosphate and other nutrients is passed to the plant roots by the fungal arbuscular structure. The first step of phosphorus uptake pathways is mediated by AM fungi which transport inorganic phosphate in soil into the root hyphae, thus this process must be dependent of phosphate transporter protein on the fungal cell membrane. Then on plants and fungi symbiotic interface, the plant phosphate transporter protein with AM specific transports inorganic phosphate to plant cortical cells. However, there are still many scientific questions not yet fully understood in these metabolic pathways, some even completely not clear. Such as the molecular mechanisms of phosphate and carbon transport in symbiotic systems, also the plant how to respond to the nutritional status of the soil to adjust the mechanism.This paper focused on expression and regulation analyses of phosphate transporter gene promoter related mycorrhizal. On the basis of two mycorrhiza-specific phosphate transporter genes named As PT1 and As PT4 isolated before, the known motif of As PT1 and As PT4 promoter sequences were searched and positioned by bioinformatics methods, then using biological software Foot Printer2.0 to predict and analysis the unknown phantoms. In this study, the known or predicted motifs were specificity knock-out by over-lap PCR, and the shuttle vector p BI121 with GUS as reporter gene was constructed. The choosed plant transformation was mediated by Agrobacterium named K599. Screened positive plants were co-cultured with Glomus intraradices BEG141, with different concentrations of phosphate to positive plants. After 4 weeks, the results of TB staining, GUS staining and GUS activity were as follows:1、In legume Astragalus sinicus, cis-acting elements MYCS and P1 BS, as known motifs of mycorrhizal specific phosphate transporter genes, played an important role in the regulation of As PT1 and As PT4.2、With various concentrations of phosphorus nutrient solution, it was found that phosphate transporter genes As PT1 and As PT4 abundantly expressed in the apical and arbuscular cells under low phosphorus, while plants and fungi rarely formed mutually beneficial symbiosis under high phosphorus.It was suggested that high-phosphorus concentration was not conducive to plant symbiosis with AM fungi, and As PT1 and As PT4 not only by the regulation of mycorrhizal fungi also Pi concentration.3、At high phosphorus concentration, nutrients was limited to transfer and transport to symbiont in plants, thus leading to the slow reaction of AM symbiosis. High phosphorus might reduce the expression of As PT4 and As PT1 or activate its negative regulatory system.4、With different phosphorus concentrations treatment, GUS gene was all expressed in As PT1 and As PT4 mutants,however, GUS activity had different degrees of decline compared to As PT1 and As PT4 with full length promoter,suggesting that different motifs had positive regulatory role on transcriptional regulation and the effect had some differences between the motifs.In summary, TAAT-motif, TAAT-motif and TGTT-motif had obvious regulation for mycorrhiza-specific phosphate transporter genes named As PT1 and As PT4 from milk vetch legume. By promoter analysis of orthologous phosphate transporter gene sequences, it was found that these elements were also widespread in other plants mycorrhiza-specific phosphate transporter gene promoters, such as rice and M. Truncatula. They might be similar to MYCS element with broad regulatory role. |
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