Phosphate transporters, PnPht1;1 and PnPht1;2 from Panax notoginseng enhance phosphate and arsenate acquisition

Abstract

Background: Panax notoginseng is a medicinally important Chinese herb with a long history of cultivation and clinical application. The planting area is mainly distributed in Wenshan Prefecture, where the quality and safety of P. notoginseng have been threatened by high concentration of arsenic (As) from the soil. The roles of phosphate (Pi) transporters involved in Pi acquisition and arsenate (AsV) tolerance were still unclear in this species. Results: In this study, two open reading frames (ORFs) of PnPht1;1 and PnPht1;2 separated from P. notoginseng were cloned based on RNA-seq, which encoded 527 and 541 amino acids, respectively. The results of relative expression levels showed that both genes responded to the Pi deficiency or As exposure, and were highly upregulated. Heterologous expression in Saccharomyces cerevisiae MB192 revealed that PnPht1;1 and PnPht1;2 performed optimally in complementing the yeast Pi-transport defect, particularly in PnPht1;2. Cells expressing PnPht1;2 had a stronger AsV tolerance than PnPht1;1-expressing cells, and accumulated less As in cells under a high-Pi concentration. Combining with the result of plasma membrane localization, these data confirmed that transporters PnPht1;1 and PnPht1;2 were putative high-affinity H + /H 2 PO 4 − symporters, mediating the uptake of Pi and AsV. Conclusion: PnPht1;1 and PnPht1;2 encoded functional plasma membrane-localized transporter proteins that mediated a putative high-affinity Pi/H + symport activity. Expression of PnPht1;1 or PnPht1;2 in mutant strains could enhance the uptake of Pi and AsV, that is probably responsible for the As accumulation in the roots of P. notoginseng.

A

“…Evidence has shown that high concentrations of external Pi competitively decrease the uptake and accumulation of As in plant, that could decrease membrane damage by lowering the activity of CAT, APX and lipid peroxidation (Gunes et al 2009;Li et al 2016). This explanation was confirmed by our previous study, in which high-concentration Pi lowered the oxidase activity of P. notoginseng, promoted the growth and improved the content of notoginsenoside, thereby decreasing the damage caused by AsV (Cao et al 2020). Therefore, Pi application may be an important strategy for As detoxification or phytoremediation in plants and phytoplankton (Kertulis et al 2005;Ye et al 2011;Yan et al 2012;Shaibur et al 2013).…”

“…Thus, the crisis of As contamination gradually entered people's view. Consistent with reports that increasing phosphorus absorption would greatly inhibit As acquisition (Luan et al 2018), our previous study found that the total As content in the notoginseng radix gradually increased with elevated AsV concentration in the soil but significantly decreased by supplementation with high-concentration Pi (Cao et al 2020). These findings suggested a similar electrochemical characteristic of phosphate and AsV, whose absorption and transport were closely associated with Pi transporters (Tang et al 2018).…”

“…In addition, the OD 600 of WT and MB192-PnPht1;3 was higher than that of MB192-YEplac112 and mutant strain MB192 under the same Pi concentration (20 or 100 μM), but a non-significant difference existed between WT and MB192-PnPht1;3. This phenomenon demonstrates that Pi addition improved the probability that Pi transporters assimilated Pi under the competition of AsV (Cao et al 2020). Another finding needs to be noted that PnPht1;3 preferred to combine Pi rather than AsV under a high concentration of Pi.…”

“…Growing media in garden pots consisted of 10% silt, 20% light aggregate, 30% clay and 40% expanded vermiculite (Mandal et al 2015), in which dissolved phosphorus content was cut down to an extremely low level by washing with 1% NaHCO 3 . Then, dissolved phosphorus concentrations were adjusted to 0.07 mM (low P, lP), 0.7 mM (medium P, mP) and 1.4 mM (high P, hP) by adding KH 2 PO 4 (Cao et al 2020). Before planting, sodium arsenate (Na 3 AsO 4 ) was thoroughly mixed into media with a 0.2 mM final concentration in dry weight for As treatment groups.…”

Sorting Nexin1 negatively modulates phosphate uptake by facilitating Phosphate Transporter1;1 degradation in Arabidopsis

“…To verify this, we tested the sensitivity of the snx1‐2 mutant to arsenate, a toxic compound with a similar structure to phosphate that can be absorbed by plant high‐affinity PHTs including PHT1;1 and PHT1;4 (Cao et al., 2020; Shin et al., 2004). Arsenate negatively affects plant growth and development such as seed germination, cotyledon greening, and root elongation (Cao et al., 2020; Shin et al., 2004; Wang et al., 2014). We found that snx1‐2 mutant seeds had comparable germination and cotyledon greening rates to wild‐type seeds when grown on arsenate‐free medium, while the mutant seeds showed significantly decreased germination and cotyledon greening rates compared to wild‐type plants when grown on arsenate‐containing medium (Figure 2a–e).…”