Function of wheat phosphate transporter gene TaPHT2;1 in Pi translocation and plant growth regulation under replete and limited Pi supply conditions

Abstract

Several phosphate transporters (PTs) that belong to the Pht2 family have been released in bioinformatics databases, but only a few members of this family have been functionally characterized. In this study, we found that wheat TaPHT2;1 shared high identity with a subset of Pht2 in diverse plants. Expression analysis revealed that TaPHT2;1 was strongly expressed in the leaves, was up-regulated by low Pi stress, and exhibited a circadian rhythmic expression pattern. TaPHT2;1-green fluorescent protein fusions in the leaves of tobacco and wheat were specifically detected in the chloroplast envelop. TaPHT2;1 complemented the Pi transporter activities in a yeast mutant with a defect in Pi uptake. Knockdown expression of TaPHT2;1 significantly reduced Pi concentration in the chloroplast under sufficient (2 mM Pi) and deficient Pi (100 μM Pi) conditions, suggesting that TaPHT2;1 is crucial in the mediation of Pi translocation from the cytosol to the chloroplast. The down-regulated expression of TaPHT2;1 resulted in reduced photosynthetic capacities, total P contents, and accumulated P amounts in plants under sufficient and deficient Pi conditions, eventually leading to worse plant growth phenotypes. The TaPHT2;1 knockdown plants exhibited pronounced decrease in accumulated phosphorus in sufficient and deficient Pi conditions, suggesting that TaPHT2;1 is an important factor to associate with a distinct P signaling that up-regulates other PT members to control Pi acquisition and translocation within plants. Therefore, TaPHT2;1 is a key member of the Pht2 family involved in Pi translocation, and that it can function in the improvement of phosphorus usage efficiency in wheat.

Efficient Mineral Nutrition: Genetic Improvement of Phosphate Uptake and Use Efficiency in Crops

“…Over-expression of AthPHR1 increased the transcript level of miRNA399 and decreased expression of PHO2, increased further the P i content and enhanced root hair density in rice and Arabidopsis (Nilsson et al 2007;Zhou et al 2008;Bustos et al 2010). Promoters of several P starvation-induced and repressed genes, including IPS and a high-affinity P-transporters, contain the P1BS cis-element (Oono et al 2011;Hammond et al 2003;Rubio et al 2001;Schünmann et al 2004;Guo et al 2013;Bustos et al 2010). In wheat, over-expression of TaPHR1 did not change transcript levels of TaPHF1, TaPHO2 or TaSPX3, whereas TaIPS and TaPht1;2 exhibited increased expression levels in the transgenic lines suggesting that transcriptional factors additional to TaPHR1 may be functional in the P starvation signalling (Wang et al 2013).…”

“…The second approach deals with the over-expression of target genes resulting in partly contradictory observations due to the expression level of their role in the P sensing and regulating network (Rae et al 2004;Zhou et al 2008;Ren et al 2012a, b;Tian et al 2012;Guo et al 2013;Wang et al 2013).…”

“…In Brassica napus, the homologue BnPHR1 was predominantly expressed in the roots exposed to P limitation and over-expression enhanced remarkably the expression of the high-affinity transporter BnPT2 (Ren et al 2012a, b). In wheat, three PHR1 homologues genes have been identified (Wang et al 2013), which regulate genes such as TaPt2;1 (Tittarelli et al 2007;Guo et al 2013) or TaIPS1 (Oono et al 2013) that have been reported to contain the P1BS element. TaPht1-A1 transcriptionally activated the expression of the phosphate transporter TaPht1;2 in yeast cells (Wang et al 2013).…”

Phosphorus Transport in Arabidopsis and Wheat: Emerging Strategies to Improve P Pool in Seeds

“…Under Pi deprivation, Pi uptake increases and involves a high-affinity PHT1 member TaPT2 ( [65]). Down-regulation of TaPHT2.1 was able to induce a pronounced decrease in Pi accumulation in both sufficient and Pi-deficient wheat, suggesting its association with other PHTs involved in Pi uptake and translocation within plants ( [41]). This reinforces the impact the intracellular Pi transport mechanism has upon regulating the plant Pi uptake efficiency.…”

“…Still, in contrast to the data known about Arabidopsis, little is known about the regulation of wheat Pi transporters at the protein levels ( [66]). It is worth to note that apart from its role in Pi uptake, TaPHT2.1 was functionally characterized as an important P signalling component involved in Pi translocation from cytosol to chloroplast in Pi-stressed leaves ( [41] [20,44]), there is no detail on their precise biological role in wheat tissues/cell. In addition, recent expression profiles of wheat PHT1 sub-family genes during hydroponic and field-grown plant tissues were correlated with the presence of cis-acting promoter elements ( [22]).…”