PLANT SIGNALING & BEHAVIOR 2016, VOL. 11, NO. 1, e1128615 (3 pages) http://dx.doi.org/10.1080/15592324.2015.1128615
SHORT COMMUNICATION
HC-pyrophosphatase from Salicornia europaea enhances tolerance to low phosphate under salinity in Arabidopsis Sulian Lv, Ping Jiang, Duoliya Wang, and Yinxin Li Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
ABSTRACT
ARTICLE HISTORY
Increasing soil salinity threatens crop productivity worldwide. High soil salinity is usually accompanied by the low availability of many mineral nutrients. Here, we investigated the potential role that the HC- PPase could play in optimizing P use efficiency under salinity in plants. Transgenic Arabidopsis plants overexpressing either SeVP1 or SeVP2 from Salicornia europaea outperformed the wild-types under low phosphate (Pi) as well as low Pi plus salt conditions. Our results suggested that HC-PPase could increase external Pi acquisition through promoting root development and upregulating phosphate transporters, thus to protect plants from Pi limiting stress. This study provides a potential strategy for improving crop yields challenged by the co-occurrence of abiotic stresses.
Received 10 November 2015 Revised 1 December 2015 Accepted 2 December 2015
Increasing soil salinity is one of the main environmental constraints on crop productivity worldwide. High soil salinity is usually accompanied by the low availability of many mineral nutrients such as nitrogen (N), phosphorus (P), and potassium (K), etc. Therefore, it is of great significance to improve these nutrients use efficiency of crops under salinity with the increasing soil salinization. As one of the proton pumps on tonoplast, HC-translocating inorganic pyrophosphatase (HC-PPase) has been demonstrated to increase salt tolerance in diverse plant species.1 Interestingly, overexpression of HC-PPase genes from Arabidopsis (AVP1) or Thellungiella halophile (TsVP) in Arabidopsis, tomato, rice or maize results in plants that outperform controls under limiting phosphorus conditions.2,3 And up-regulation of AVP1 can improve the N use efficiency in romaine lettuce.4 Thus, genetic manipulation of type I HC-PPase appears to be a generally applicable technology to help alleviate agricultural losses in salinity, low phosphorus and low nitrogen soils. Recently, we found that HC-PPase is involved in salt stimulated NO3¡ uptake in the euhalophyte Salicornia europaea. Furthermore, overexpression of genes (SeVP1 and SeVP2) encoding this enzyme in Arabidopsis and wheat confers tolerance to simultaneously occurring salt stress and nitrogen deficiency.5 Here, we investigated the performance of Arabidopsis plants from the same transgenic lines under low Pi as well as low Pi plus salt conditions. For this purpose, 4-d-old seedlings were subjected to low Pi (10 mM KH2PO4, LP) and low Pi plus salt (10 mM KH2PO4 with 100 mM NaCl, LPCS) stresses, with plants grown in 0.5£MS containing 1 mM KH2PO4 (HP) and HPCS as the controls, respectively. The characterization of these transgenic plants overexpressing SeVP1 or SeVP2 under LP and LPCS conditions revealed an obvious advantage in terms of both shoot and root development (Fig. 1). Transgenic
CONTACT Yinxin Li
[email protected]
© 2016 Taylor & Francis Group, LLC
KEYWORDS
Co-occurrence of stresses; HC-pyrophosphatase; low phosphate; salt; salicornia europaea
plants overexpressing SeVP1 and SeVP2 showed longer primary roots and developed more lateral roots than the wild-types (WT) under LP as well as LPCS conditions (Fig. 1B-C). Of note, after 8 d of treatment, the fresh weight of transgenic seedlings were significantly higher than that of WT, with an increase of 11-45%, 27-46% and 33-54% under salt, LP and LPCS conditions, respectively (Fig. 1D). The enhanced tolerance to LP and LPCS in SeVP1 and SeVP2-overexpressing plants was further confirmed when 21d-old plants grown in hydroponic conditions were subjected to 0.5£Hoagland’s solution containing 100 mM NaCl (S), LP and LPCS stress for 10 days, respectively. Further experiments indicated increased external Pi acquisition occurred in the transgenic lines (Fig. 1E). Under the control conditions (HP), the transgenic lines had a mean 20% higher plant P content than WT; while under LP conditions, the mean P content in the transgenic lines was about 2 times of that in WT. Under salt and LPCS stress, these values were 94% and 79%, respectively. Consistent with the higher P content in the transgenic plants, the expression levels of 4 phosphate transporter genes including AtPht1;2, AtPht1;4, AtPht1;8 and AtPht1;9, which are responsible for Pi acquisition from soil,6-8 were constitutively higher in these transgenic plants than those in WT ones (Fig. 2). Taken together, our results suggested that HC-PPase could increase external Pi acquisition through promoting root development as well as upregulation the expression of phosphate transporter genes, thus to protect plants from Pi limiting stress. Then, how can the up-regulation of HC-PPase promote root development and increase expression of phosphate transporter genes? It is presumed that Pi starvation increases allocation of available photosynthates to roots to promote Pi acquisition. One consequence of the increased
e1128615-2
S. LV ET AL.
Figure 1. Phenotypes, growth parameters and total (P)content of WT and transgenic Arabidopsis seedlings under stress conditions. (A) Phenotypes, (B) root length, (C) number of lateral roots, (D) fresh weight, and (E) total P content. For growth parameters detection, 4-d-old seedlings were transferred to the 4 treated 0.5£MS medium containing 1 mM KH2PO4 (HP), 1 mM KH2PO4 and 100 mM NaCl (HPCS), 10 mM KH2PO4 (LP), 10 mM KH2PO4 and 100 mM NaCl (LPCS) for 8 days, respectively. For total P content detection, 21-d-old plants grown in 0.5£Hoagland solution were subjected to the above stresses for 10 days, respectively. WT, Arabidopsis ecotypes Col-0; VP1-3 and VP1-6, SeVP1-overexpression lines; VP2-1 and VP2-3, SeVP2-overexpression lines. Values are means § SD (n D 9 for B and C; n D 4 for D; n D 3 for E). Asterisks indicate a significant difference from the WT under the same treatment conditions at P < 0.05 or P < 0.01 by t-test. Scale bar D 2 cm.
delivery of sugars to plant roots is enhancement of root proliferation.9 In addition, the Suc delivered to the root acts as a systemic signal to up-regulate genes encoding phosphate transporters, phosphatases, and metabolic enzymes in combination with the PHR1 transcriptional cascade under low Pi conditions, while its effects on lateral rooting occur through the modulation of auxin transport.10 Previously, we have concluded that HC-PPase favors the transport of photosynthates to root, on the basis of results from carbohydrates detection in shoot and root, and the upregulation of
3 sugar transporter genes encoding AtSUC1, AtSUC2 and AtTMT1 in the transgenic Arabidopsis.5 Furthermore, 14 C-labeling experiments in transgenic Arabidopsis overexpressing AVP1 showed enhanced photosynthesis, phloem loading, phloem transport, and delivery to sink organs.11 Thus, the up-regulation of HC-PPase may enhance root development and phosphate transporter genes expression by increasing delivery of sugars to roots under low Pi conditions. Then, how does HC-PPase work in Suc phloem loading and transport? Previously, a model has been suggested, where the
Figure 2. Expression patterns of phosphate transporter genes in WT, VP1-3 and VP2-3 plants under HP and LP conditions. Twenty-one days old of WT and transgenic plants grown in 0.5£Hoagland’s solution were transferred into treat solution supplied with 1 mM KH2PO4 (HP), and 10 mM KH2PO4 (LP), respectively. Roots from 3 plants under all treatments were sampled at 3 d. The AtActin gene was used as an internal control. Vertical bars indicate § SD of 3 replicates on one sample. Three biological experiments were performed, which produced similar results.
PLANT SIGNALING & BEHAVIOR
type I HC-PPases localized in the PM of sieve element-companion cell complexes (SE-CCc) is proposed to be function as PPi synthases to regulate Suc respiration for the ATP and PM proton motive force (PMF) required for Suc phloem loading.1 Most recently, 2 researches evidenced this model through genetic, histochemical and physiological analysis of Arabidopsis plants with constitutive and CC-specific overexpression of AVP1.11,12 According to these results, we suggest that under co-occurrence of salt stress and low Pi or NO3¡ conditions, HC-PPases localized in the tonoplast function as proton pumping pyrophosphatase energize the endomembrane compartments to increase NaC compartmentalization, meanwhile, HCPPases localized in the PM of SE-CCc function as a synthase to synthesize PPi that promotes Suc phloem loading and transport, which can induce root development as well as expression of Pi or NO3¡ transporter genes. In conclusion, our studies indicated that HC-PPase genes can be potential in development of new transgenic crops with high N, P or other nutrients use efficiency under salinity, which provides potential strategies for improving crop yields challenged by increasing soil salinization and shrinking farmland.
3.
4.
5.
6.
7.
8.
Disclosure of potential conflicts of interest No potential conflicts of interest were disclosed. 9.
Acknowledgments This work was supported by the National Natural Science Foundation of China (grant no. 31270421) and the Science and Technology Service Network Initiative of the Chinese Academy of Sciences (grant no. KFJ-EWSTS-061-4).
10.
11.
References 1. Gaxiola RA, Sanchez CA, Paez-Valencia J, Ayre BG, Elser JJ. Genetic manipulation of a “vacuolar” HC-PPase: from salt tolerance to yield enhancement under phosphorus-deficient soils. Plant Physiol 2012; 159:3-11; PMID:22434041; http://dx.doi.org/10.1104/pp.112.195701 2. Yang H, Knapp J, Koirala P, Rajagopal D, Peer WA, Silbart LK, Murphy A, Gaxiola RA. Enhanced phosphorus nutrition in monocots and dicots over-expressing a phosphorus-responsive type I HC-pyrophos-
12.
e1128615-3
phatase. Plant Biotechnol J 2007; 5:735-45; PMID:17711412; http:// dx.doi.org/10.1111/j.1467-7652.2007.00281.x Pei LM, Wang JM, Li KP, Li YJ, Li B, Gao F, Yang A. Overexpression of Thellungiella halophila HC-pyrophosphatase gene improves low phosphate tolerance in maize. PLoS One 2012; 7(8):e43501; PMID: 22952696; http://dx.doi.org/10.1371/journal.pone.0043501 Paez-Valencia J, Sanchez-Lares J, Marsh E, Dorneles LT, Santos MP, Sanchez D, Winter A, Murphy S, Cox J, Trzaska M, et al. Enhanced proton translocating pyrophosphatase activity improves nitrogen use efficiency in romaine lettuce. Plant Physiol 2013; 161:1557-69; PMID:23307651; http://dx.doi.org/10.1104/pp.112.212852 Lv SL, Jiang P, Nie LL, Chen XY, Tai F, Wang D, Fan P, Feng J, Bao H, Wang J, et al. HC-pyrophosphatase from Salicornia europaea confers tolerance to simultaneously occurring salt stress and nitrogen deficiency in Arabidopsis and wheat. Plant Cell Environ 2015; 38 (11):2433-49; PMID:25920512; http://dx.doi.org/10.1111/pce.12557 Misson J, Thibaud MC, Bechtold N, Raghothama K, Nussaume L. Transcriptional regulation and functional properties of Arabidopsis Pht1;4, a high affinity transporter contributing greatly to phosphate uptake in phosphate deprived plants. Plant Mol Biol 2004; 55:727-41; PMID:15604713; http://dx.doi.org/10.1007/s11103-004-1965-5 Shin H, Shin HS, Dewbre GR, Harrison MJ. Phosphate transport in Arabidopsis: Pht1;1 and Pht1;4 play a major role in phosphate acquisition from both low- and high-phosphate environments. Plant J 2004; 39:629-42; PMID:15272879; http://dx.doi.org/10.1111/j.1365313X.2004.02161.x Remy E, Cabrito TR, Batista RA, Teixeira MC, Sa-Correia I, Duque P. The Pht1;9 and Pht1;8 transporters mediate inorganic phosphate acquisition by the Arabidopsis thaliana root during phosphorus starvation. New Phytol 2012; 195:356-71; PMID:22578268; http://dx.doi. org/10.1111/j.1469-8137.2012.04167.x Hammond JP, White PJ. Sucrose transport in the phloem: integrating root responses to phosphorus starvation. J Exp Bot 2008; 59:93-109; PMID:18212031; http://dx.doi.org/10.1093/jxb/erm221 Hammond JP, White PJ. Sugar signaling in root responses to low phosphorus availability. Plant Physiol 2011; 156:1033-40; PMID:21487049; http://dx.doi.org/10.1104/pp.111.175380 Khadilkar AS, Yadav UP, Salazar C, Shulaev V, Paez-Valencia J, Pizzio GA, Gaxiola RA, Ayre BG. Constitutive and companion cell-specific overexpression of AVP1, encoding a proton pumping pyrophosphatase, enhances biomass accumulation, phloem loading and long distance transport. Plant Physiol 2016; 170(1):401-414; PMID:26530315; http://dx.doi.org/10.1104/pp.15.01409 Pizzio GA, Paez-Valencia J, Khadilkar AS, Regmi K, Patron-Soberano A, Zhang SJ, Sanchez-Lares J, Furstenau T, Li J, Sanchez-Gomez C, et al. Arabidopsis type I proton-pumping pyrophosphatase expresses strongly in phloem, where it is required for pyrophosphate metabolism and photosynthate partitioning. Plant Physiol 2015; 167:1541-53; PMID:25681328; http://dx.doi.org/10.1104/pp.114.254342
SHORT COMMUNICATION
HC-pyrophosphatase from Salicornia europaea enhances tolerance to low phosphate under salinity in Arabidopsis Sulian Lv, Ping Jiang, Duoliya Wang, and Yinxin Li Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
ABSTRACT
ARTICLE HISTORY
Increasing soil salinity threatens crop productivity worldwide. High soil salinity is usually accompanied by the low availability of many mineral nutrients. Here, we investigated the potential role that the HC- PPase could play in optimizing P use efficiency under salinity in plants. Transgenic Arabidopsis plants overexpressing either SeVP1 or SeVP2 from Salicornia europaea outperformed the wild-types under low phosphate (Pi) as well as low Pi plus salt conditions. Our results suggested that HC-PPase could increase external Pi acquisition through promoting root development and upregulating phosphate transporters, thus to protect plants from Pi limiting stress. This study provides a potential strategy for improving crop yields challenged by the co-occurrence of abiotic stresses.
Received 10 November 2015 Revised 1 December 2015 Accepted 2 December 2015
Increasing soil salinity is one of the main environmental constraints on crop productivity worldwide. High soil salinity is usually accompanied by the low availability of many mineral nutrients such as nitrogen (N), phosphorus (P), and potassium (K), etc. Therefore, it is of great significance to improve these nutrients use efficiency of crops under salinity with the increasing soil salinization. As one of the proton pumps on tonoplast, HC-translocating inorganic pyrophosphatase (HC-PPase) has been demonstrated to increase salt tolerance in diverse plant species.1 Interestingly, overexpression of HC-PPase genes from Arabidopsis (AVP1) or Thellungiella halophile (TsVP) in Arabidopsis, tomato, rice or maize results in plants that outperform controls under limiting phosphorus conditions.2,3 And up-regulation of AVP1 can improve the N use efficiency in romaine lettuce.4 Thus, genetic manipulation of type I HC-PPase appears to be a generally applicable technology to help alleviate agricultural losses in salinity, low phosphorus and low nitrogen soils. Recently, we found that HC-PPase is involved in salt stimulated NO3¡ uptake in the euhalophyte Salicornia europaea. Furthermore, overexpression of genes (SeVP1 and SeVP2) encoding this enzyme in Arabidopsis and wheat confers tolerance to simultaneously occurring salt stress and nitrogen deficiency.5 Here, we investigated the performance of Arabidopsis plants from the same transgenic lines under low Pi as well as low Pi plus salt conditions. For this purpose, 4-d-old seedlings were subjected to low Pi (10 mM KH2PO4, LP) and low Pi plus salt (10 mM KH2PO4 with 100 mM NaCl, LPCS) stresses, with plants grown in 0.5£MS containing 1 mM KH2PO4 (HP) and HPCS as the controls, respectively. The characterization of these transgenic plants overexpressing SeVP1 or SeVP2 under LP and LPCS conditions revealed an obvious advantage in terms of both shoot and root development (Fig. 1). Transgenic
CONTACT Yinxin Li
[email protected]
© 2016 Taylor & Francis Group, LLC
KEYWORDS
Co-occurrence of stresses; HC-pyrophosphatase; low phosphate; salt; salicornia europaea
plants overexpressing SeVP1 and SeVP2 showed longer primary roots and developed more lateral roots than the wild-types (WT) under LP as well as LPCS conditions (Fig. 1B-C). Of note, after 8 d of treatment, the fresh weight of transgenic seedlings were significantly higher than that of WT, with an increase of 11-45%, 27-46% and 33-54% under salt, LP and LPCS conditions, respectively (Fig. 1D). The enhanced tolerance to LP and LPCS in SeVP1 and SeVP2-overexpressing plants was further confirmed when 21d-old plants grown in hydroponic conditions were subjected to 0.5£Hoagland’s solution containing 100 mM NaCl (S), LP and LPCS stress for 10 days, respectively. Further experiments indicated increased external Pi acquisition occurred in the transgenic lines (Fig. 1E). Under the control conditions (HP), the transgenic lines had a mean 20% higher plant P content than WT; while under LP conditions, the mean P content in the transgenic lines was about 2 times of that in WT. Under salt and LPCS stress, these values were 94% and 79%, respectively. Consistent with the higher P content in the transgenic plants, the expression levels of 4 phosphate transporter genes including AtPht1;2, AtPht1;4, AtPht1;8 and AtPht1;9, which are responsible for Pi acquisition from soil,6-8 were constitutively higher in these transgenic plants than those in WT ones (Fig. 2). Taken together, our results suggested that HC-PPase could increase external Pi acquisition through promoting root development as well as upregulation the expression of phosphate transporter genes, thus to protect plants from Pi limiting stress. Then, how can the up-regulation of HC-PPase promote root development and increase expression of phosphate transporter genes? It is presumed that Pi starvation increases allocation of available photosynthates to roots to promote Pi acquisition. One consequence of the increased
e1128615-2
S. LV ET AL.
Figure 1. Phenotypes, growth parameters and total (P)content of WT and transgenic Arabidopsis seedlings under stress conditions. (A) Phenotypes, (B) root length, (C) number of lateral roots, (D) fresh weight, and (E) total P content. For growth parameters detection, 4-d-old seedlings were transferred to the 4 treated 0.5£MS medium containing 1 mM KH2PO4 (HP), 1 mM KH2PO4 and 100 mM NaCl (HPCS), 10 mM KH2PO4 (LP), 10 mM KH2PO4 and 100 mM NaCl (LPCS) for 8 days, respectively. For total P content detection, 21-d-old plants grown in 0.5£Hoagland solution were subjected to the above stresses for 10 days, respectively. WT, Arabidopsis ecotypes Col-0; VP1-3 and VP1-6, SeVP1-overexpression lines; VP2-1 and VP2-3, SeVP2-overexpression lines. Values are means § SD (n D 9 for B and C; n D 4 for D; n D 3 for E). Asterisks indicate a significant difference from the WT under the same treatment conditions at P < 0.05 or P < 0.01 by t-test. Scale bar D 2 cm.
delivery of sugars to plant roots is enhancement of root proliferation.9 In addition, the Suc delivered to the root acts as a systemic signal to up-regulate genes encoding phosphate transporters, phosphatases, and metabolic enzymes in combination with the PHR1 transcriptional cascade under low Pi conditions, while its effects on lateral rooting occur through the modulation of auxin transport.10 Previously, we have concluded that HC-PPase favors the transport of photosynthates to root, on the basis of results from carbohydrates detection in shoot and root, and the upregulation of
3 sugar transporter genes encoding AtSUC1, AtSUC2 and AtTMT1 in the transgenic Arabidopsis.5 Furthermore, 14 C-labeling experiments in transgenic Arabidopsis overexpressing AVP1 showed enhanced photosynthesis, phloem loading, phloem transport, and delivery to sink organs.11 Thus, the up-regulation of HC-PPase may enhance root development and phosphate transporter genes expression by increasing delivery of sugars to roots under low Pi conditions. Then, how does HC-PPase work in Suc phloem loading and transport? Previously, a model has been suggested, where the
Figure 2. Expression patterns of phosphate transporter genes in WT, VP1-3 and VP2-3 plants under HP and LP conditions. Twenty-one days old of WT and transgenic plants grown in 0.5£Hoagland’s solution were transferred into treat solution supplied with 1 mM KH2PO4 (HP), and 10 mM KH2PO4 (LP), respectively. Roots from 3 plants under all treatments were sampled at 3 d. The AtActin gene was used as an internal control. Vertical bars indicate § SD of 3 replicates on one sample. Three biological experiments were performed, which produced similar results.
PLANT SIGNALING & BEHAVIOR
type I HC-PPases localized in the PM of sieve element-companion cell complexes (SE-CCc) is proposed to be function as PPi synthases to regulate Suc respiration for the ATP and PM proton motive force (PMF) required for Suc phloem loading.1 Most recently, 2 researches evidenced this model through genetic, histochemical and physiological analysis of Arabidopsis plants with constitutive and CC-specific overexpression of AVP1.11,12 According to these results, we suggest that under co-occurrence of salt stress and low Pi or NO3¡ conditions, HC-PPases localized in the tonoplast function as proton pumping pyrophosphatase energize the endomembrane compartments to increase NaC compartmentalization, meanwhile, HCPPases localized in the PM of SE-CCc function as a synthase to synthesize PPi that promotes Suc phloem loading and transport, which can induce root development as well as expression of Pi or NO3¡ transporter genes. In conclusion, our studies indicated that HC-PPase genes can be potential in development of new transgenic crops with high N, P or other nutrients use efficiency under salinity, which provides potential strategies for improving crop yields challenged by increasing soil salinization and shrinking farmland.
3.
4.
5.
6.
7.
8.
Disclosure of potential conflicts of interest No potential conflicts of interest were disclosed. 9.
Acknowledgments This work was supported by the National Natural Science Foundation of China (grant no. 31270421) and the Science and Technology Service Network Initiative of the Chinese Academy of Sciences (grant no. KFJ-EWSTS-061-4).
10.
11.
References 1. Gaxiola RA, Sanchez CA, Paez-Valencia J, Ayre BG, Elser JJ. Genetic manipulation of a “vacuolar” HC-PPase: from salt tolerance to yield enhancement under phosphorus-deficient soils. Plant Physiol 2012; 159:3-11; PMID:22434041; http://dx.doi.org/10.1104/pp.112.195701 2. Yang H, Knapp J, Koirala P, Rajagopal D, Peer WA, Silbart LK, Murphy A, Gaxiola RA. Enhanced phosphorus nutrition in monocots and dicots over-expressing a phosphorus-responsive type I HC-pyrophos-
12.
e1128615-3
phatase. Plant Biotechnol J 2007; 5:735-45; PMID:17711412; http:// dx.doi.org/10.1111/j.1467-7652.2007.00281.x Pei LM, Wang JM, Li KP, Li YJ, Li B, Gao F, Yang A. Overexpression of Thellungiella halophila HC-pyrophosphatase gene improves low phosphate tolerance in maize. PLoS One 2012; 7(8):e43501; PMID: 22952696; http://dx.doi.org/10.1371/journal.pone.0043501 Paez-Valencia J, Sanchez-Lares J, Marsh E, Dorneles LT, Santos MP, Sanchez D, Winter A, Murphy S, Cox J, Trzaska M, et al. Enhanced proton translocating pyrophosphatase activity improves nitrogen use efficiency in romaine lettuce. Plant Physiol 2013; 161:1557-69; PMID:23307651; http://dx.doi.org/10.1104/pp.112.212852 Lv SL, Jiang P, Nie LL, Chen XY, Tai F, Wang D, Fan P, Feng J, Bao H, Wang J, et al. HC-pyrophosphatase from Salicornia europaea confers tolerance to simultaneously occurring salt stress and nitrogen deficiency in Arabidopsis and wheat. Plant Cell Environ 2015; 38 (11):2433-49; PMID:25920512; http://dx.doi.org/10.1111/pce.12557 Misson J, Thibaud MC, Bechtold N, Raghothama K, Nussaume L. Transcriptional regulation and functional properties of Arabidopsis Pht1;4, a high affinity transporter contributing greatly to phosphate uptake in phosphate deprived plants. Plant Mol Biol 2004; 55:727-41; PMID:15604713; http://dx.doi.org/10.1007/s11103-004-1965-5 Shin H, Shin HS, Dewbre GR, Harrison MJ. Phosphate transport in Arabidopsis: Pht1;1 and Pht1;4 play a major role in phosphate acquisition from both low- and high-phosphate environments. Plant J 2004; 39:629-42; PMID:15272879; http://dx.doi.org/10.1111/j.1365313X.2004.02161.x Remy E, Cabrito TR, Batista RA, Teixeira MC, Sa-Correia I, Duque P. The Pht1;9 and Pht1;8 transporters mediate inorganic phosphate acquisition by the Arabidopsis thaliana root during phosphorus starvation. New Phytol 2012; 195:356-71; PMID:22578268; http://dx.doi. org/10.1111/j.1469-8137.2012.04167.x Hammond JP, White PJ. Sucrose transport in the phloem: integrating root responses to phosphorus starvation. J Exp Bot 2008; 59:93-109; PMID:18212031; http://dx.doi.org/10.1093/jxb/erm221 Hammond JP, White PJ. Sugar signaling in root responses to low phosphorus availability. Plant Physiol 2011; 156:1033-40; PMID:21487049; http://dx.doi.org/10.1104/pp.111.175380 Khadilkar AS, Yadav UP, Salazar C, Shulaev V, Paez-Valencia J, Pizzio GA, Gaxiola RA, Ayre BG. Constitutive and companion cell-specific overexpression of AVP1, encoding a proton pumping pyrophosphatase, enhances biomass accumulation, phloem loading and long distance transport. Plant Physiol 2016; 170(1):401-414; PMID:26530315; http://dx.doi.org/10.1104/pp.15.01409 Pizzio GA, Paez-Valencia J, Khadilkar AS, Regmi K, Patron-Soberano A, Zhang SJ, Sanchez-Lares J, Furstenau T, Li J, Sanchez-Gomez C, et al. Arabidopsis type I proton-pumping pyrophosphatase expresses strongly in phloem, where it is required for pyrophosphate metabolism and photosynthate partitioning. Plant Physiol 2015; 167:1541-53; PMID:25681328; http://dx.doi.org/10.1104/pp.114.254342
