than direct uptake by roots which is performed by high affinity transporters such as
OsPht1;6 (OsPT6) and HORvu-Pht1;1 (Rae et al. 2003; Ai et al. 2009). Members of
the PHT1 family are the primary ion channel transporters present on the outer
cortical cells and epidermal cells of root, and responsible for uptake of Pi. In addition
to this primary role, members of PHT1 family are also believed to be involved in
translocation and distribution owing to their presence in various other plant organs
such as young and mature leaves, stems, anther, silk, young seed, cobs, stages of
pollen grains (Davies et al. 2002; Nagy et al. 2006; Ai et al. 2009).
PHT2 family are low-affinity proton symporters (H+/Pi cotransporter) that have
been shown to be up-regulated under P-starvation stress, help in translocating
phosphate to green shoot tissues and chloroplast (Daram et al. 1999; Versaw and
Harrison 2002; Guo et al. 2013). PHT2 has been suggested to be a key regulator of
signaling under both P-deficient and P-sufficient condition, and may control other
phosphate transporters responsible for Pi acquisition and translocation. The third
family of transporters, PHT3, is involved in uptake of P in mitochondria
(Takabatake et al. 1999; Rausch and Bucher 2002); and the fourth family—PHT4
is known to play role in intra-cellular Pi translocation, viz. within cytosol, chloroplast, plastids, and the Golgi apparatus (Guo et al. 2008; Cubero et al. 2009; Liu et al.
2011). PHT4;6 in A. thaliana has been shown to be localized to Golgi body, is
regulated by circadian rhythm, and plays roles in both biotic and abiotic stress
responses (Cubero et al. 2009; Wang et al. 2011).
Apart from transporters, several other molecular regulators play important role in
P-sensing, uptake, transport, and acquisition. Products of PDR2 (Phosphate Deficiency Response 2), LPR1 (Low Phosphate Root 1), and LPR2 are involved in local
sensing of available phosphate levels proximal to Arabidopsis thaliana roots
(Lopez-Arredondo et al. 2014). The local sensing of phosphate availability and
uptake is modulated by regulating the root meristem activity through interaction of
PDR2, LPR1, SCR, SHR (Ticconi et al. 2009). PHR1 (phosphate starvation responsive 1), which is a R2-R3 MYB transcription factor, also plays a critical role in
sensing P availability (Rubio et al. 2001). It binds to P1BS DNA motif
(GNATATNC; Rubio et al. 2001) which is conserved in monocots as well as dicots
(Zhou et al. 2008). This motif is found in several putative phosphate starvation
responsive genes such as PHT1 (Bustos et al. 2010) and INDUCED BY PHOSPHATE STARVATION gene (IPS, Rubio et al. 2001). These constitute the primary
sensing mechanism, present upstream of the Pi uptake by high affinity PHT1
transporter. Several other studies have investigated post-transcriptional regulation
of PHT1 such as through intracellular trafficking by PHF1 (González et al. 2005;
Bayle et al. 2011), phosphorylation at C’-terminal end (Bayle et al. 2011), and
endocytosis followed by subsequent degradation of transporter protein by PHO84
(Lagerstedt et al. 2002; Persson et al. 2003). The two genes PHO1 and PHO2 are
responsible for Pi homeostasis (Hamburger et al. 2002; Aung et al. 2006; Bari et al.
2006). Several secondary messengers such as Ca
2+ , IPs (Stevenson-Paulik et al.
2005), ROS (Tyburski et al. 2009) are known to be induced by phosphate starvation
and may play role in sensing and signaling of phosphate levels.
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 147
OsPht1;6 (OsPT6) and HORvu-Pht1;1 (Rae et al. 2003; Ai et al. 2009). Members of
the PHT1 family are the primary ion channel transporters present on the outer
cortical cells and epidermal cells of root, and responsible for uptake of Pi. In addition
to this primary role, members of PHT1 family are also believed to be involved in
translocation and distribution owing to their presence in various other plant organs
such as young and mature leaves, stems, anther, silk, young seed, cobs, stages of
pollen grains (Davies et al. 2002; Nagy et al. 2006; Ai et al. 2009).
PHT2 family are low-affinity proton symporters (H+/Pi cotransporter) that have
been shown to be up-regulated under P-starvation stress, help in translocating
phosphate to green shoot tissues and chloroplast (Daram et al. 1999; Versaw and
Harrison 2002; Guo et al. 2013). PHT2 has been suggested to be a key regulator of
signaling under both P-deficient and P-sufficient condition, and may control other
phosphate transporters responsible for Pi acquisition and translocation. The third
family of transporters, PHT3, is involved in uptake of P in mitochondria
(Takabatake et al. 1999; Rausch and Bucher 2002); and the fourth family—PHT4
is known to play role in intra-cellular Pi translocation, viz. within cytosol, chloroplast, plastids, and the Golgi apparatus (Guo et al. 2008; Cubero et al. 2009; Liu et al.
2011). PHT4;6 in A. thaliana has been shown to be localized to Golgi body, is
regulated by circadian rhythm, and plays roles in both biotic and abiotic stress
responses (Cubero et al. 2009; Wang et al. 2011).
Apart from transporters, several other molecular regulators play important role in
P-sensing, uptake, transport, and acquisition. Products of PDR2 (Phosphate Deficiency Response 2), LPR1 (Low Phosphate Root 1), and LPR2 are involved in local
sensing of available phosphate levels proximal to Arabidopsis thaliana roots
(Lopez-Arredondo et al. 2014). The local sensing of phosphate availability and
uptake is modulated by regulating the root meristem activity through interaction of
PDR2, LPR1, SCR, SHR (Ticconi et al. 2009). PHR1 (phosphate starvation responsive 1), which is a R2-R3 MYB transcription factor, also plays a critical role in
sensing P availability (Rubio et al. 2001). It binds to P1BS DNA motif
(GNATATNC; Rubio et al. 2001) which is conserved in monocots as well as dicots
(Zhou et al. 2008). This motif is found in several putative phosphate starvation
responsive genes such as PHT1 (Bustos et al. 2010) and INDUCED BY PHOSPHATE STARVATION gene (IPS, Rubio et al. 2001). These constitute the primary
sensing mechanism, present upstream of the Pi uptake by high affinity PHT1
transporter. Several other studies have investigated post-transcriptional regulation
of PHT1 such as through intracellular trafficking by PHF1 (González et al. 2005;
Bayle et al. 2011), phosphorylation at C’-terminal end (Bayle et al. 2011), and
endocytosis followed by subsequent degradation of transporter protein by PHO84
(Lagerstedt et al. 2002; Persson et al. 2003). The two genes PHO1 and PHO2 are
responsible for Pi homeostasis (Hamburger et al. 2002; Aung et al. 2006; Bari et al.
2006). Several secondary messengers such as Ca
2+ , IPs (Stevenson-Paulik et al.
2005), ROS (Tyburski et al. 2009) are known to be induced by phosphate starvation
and may play role in sensing and signaling of phosphate levels.
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 147