Agriculture Reference
In-Depth Information
Targeting the P
i
transporters to the plasma membrane via the secretory traffick-
ing pathway is mediated by PHF genes (phosphate transporter traffic facilitator 1),
which are expressed strongly in root tissues and in leaf mesophyll cells, mimicking
the expression pattern of the Pht1 gene family (Gonz
´
lez et al.
2005
; Chen
et al.
2011
). OsPHF1 and OsPHF1L (Chen et al.
2011
) and TaPHF1 (Wang
et al.
2013
) in rice and wheat, which are homologous genes to AtPHF1 in
Arabidopsis
(Gonz
´
lez et al.
2005
; Bayle et al.
2011
), are localised specifically in
the endoplasmic reticulum (Gonz´lez et al.
2005
; Bayle et al.
2011
). AthPHF1
encodes for a plant-specific protein structurally related to SEC12 proteins of the
early secretory pathway (Gonz´lez et al.
2005
). The exit of Pht1 transporter from
the endoplasmic reticulum and the targeting through the endosomal compartments
are modulated by phosphorylation (Bayle et al.
2011
). The
phf1
mutation in
Arabidopsis
impairs P
i
uptake and P
i
transport (Gonz´lez et al.
2005
). In rice, it
decreases excessive shoot P
i
accumulation and P
i
concentrations in leaves and roots
driven by OsPHR2 and OsPHF1 over-expression (Chen et al.
2011
). Even under
P-replete experimental conditions, expression of phosphate starvation-induced
genes (PSI) was induced in
Osphf1-1
mutants due to impaired plasma membrane
location of the low-affinity P transporter OsPT2 and a high-affinity P transporter
OsPht1;8 (Cheng et al.
2011
).
Increasing expression of Pht1 transporters was observed as a response to P
starvation or mycorrhizal infection, exhibiting a large diversity of expression pat-
terns throughout the plant tissues. However, the lack of complete genome sequence
information has hindered detailed investigation in wheat. Pht1 transporters, which
are preferentially or exclusively expressed in roots, were found in barley (Smith
et al.
1999
; Rae et al.
2003
), wheat (Davies et al.
2002
; Teng et al.
2013
; Wang
et al.
2013
),
Arabidopsis
(Mudge et al.
2002
; Muchhal et al.
1996
), rice (Paszkowski
et al.
2002
) maize (Nagy et al.
2006
) and tomato (Liu et al. 1998; Muchhal and
Raghothama
1999
). Furthermore, Pht1 expression in shoot tissues has been reported
e.g. in phloem of older leaves, flag leaves or sheaths of barley (Rae et al.
2003
), in the
panicle at the heading stage and flag leaves after heading in rice (Liu et al.
2011
), in
mature pollen of
Arabidopsis
(Mudge et al.
2002
) or during mycorrhizal infection in
roots of rice (Paszkowski et al.
2002
; Yang et al.
2012
), wheat (Glassop et al.
2005
),
Brachypodium
(Hong et al.
2012
) and
Medicago
(Gaude et al.
2012
).
The specificity of Pht1 expression to arbuscular mycorrhiza (AM) colonisation
has been investigated in cereal species and was considered symbiosis specific
(Harrison et al.
2002
; Gutjahr et al.
2008
; Glassop et al.
2005
; Paszkowski
et al.
2002
), as for instance for the expression of OsPT1;11 (Gutjahr et al.
2008
;
Paszkowski et al.
2002
) and OsPT1;13 (Yang et al.
2012
;G¨ imil et al.
2005
) in rice.
Homologues of both genes occur in
Brachypodium
(Hong et al.
2012
) and maize
(Nagy et al.
2006
), where transcripts also accumulated in non-colonised roots and
leaves, suggesting additional roles during P starvation (Yang et al.
2012
).
The Pht1 promoters contain the target elements for transcription factors of the P
signalling network, for instance the P1BS
cis
-element as a target for PHR1
(Sch¨nmann et al.
2004
; Ren et al.
2012a
) or the WRKY-binding W-box as a target
