Agriculture Reference
In-Depth Information
role of a protein kinase, OsPupK46-2, within the
Pup1
locus (
Phosphorus uptake
1
), which is a major QTL for low P tolerance in rice (Gamuyao et al.
2012
).
Pht1 phosphate transporter genes are also regulated at the post-transcriptional
level by the recently discovered PHF1 in rice and
Arabidopsis
(Chen et al.
2011
;
Bayle et al.
2011
; Chiou and Lin
2011
), which is connected to a kinase,
RAPTOR1B. PHR1 is up-regulated at the transcript level and both are
up-regulated at the protein-level in P-starved roots of
Arabidopsis
(Lan
et al.
2012
). The enhanced synthesis of organic acids allows P recycling from
phosphorylated glycolytic intermediates, particularly phosphoenolpyruvate (PEP),
which is mediated via the enzyme phosphoenolpyruvate carboxylase (PEPC).
PEPC is in turn activated by reversible phosphorylation via PPCK (PEPC kinase)
(Gregory et al.
2009
). PPCK has been reported as being among up-regulated genes
during P starvation (Morcuende et al.
2007
;M¨ ller et al. 2007; Chen et al.
2007
).
Therefore, PEP and PEPC are among the metabolites and enzymes, which are more
abundant or active in P starved
A. thaliana, B. nigra, O. sativa
and
T. aestivum
(Morcuende et al.
2007
; Johnson et al.
1996
; Duff et al.
1989
; Oono et al.
2011
;
Neumann and R¨mheld
1999
).
In
Arabidopsis
, PHR1, which initiates P starvation signalling responses, was
hypothesised to be a target for the conjugation of the SUMO superfamily of proteins
via SUMO ligases (sumoylation; Miura et al.
2005
; Wang et al.
2013
). The
sumoylation is mediated by the small ubiquitin like modifier SUMO E3 ligase,
AtSIZ1, which is more root than shoot abundant and is localised in the nucleus of
the cells (Miura et al.
2005
). The homologue, OsSIZ1, have been also detected
among transcripts of P starved rice (Oono et al.
2011
). The observation that AtIPS
gene induction was reduced in
siz1
mutants, indicating a positive regulation with
AtSIZ1, (Miura et al.
2005
), strengthens the hypothesis that post-translational
modifications as essential for the initial stages of P starvation signalling cascades.
Additionally, AtSIZI negatively regulates P starvation-dependent primary root
growth inhibition (increased root hair number and length) through the control of
auxin patterning (Miura et al.
2011
), whereas the
phr1
mutant does not exhibit
affected root architecture (Rubio et al.
2001
).
In conclusion, post-translational modifications may be essential leaders for P
economy in plants (Raven
2008
) and potentially for enhancing PUE in crops.
PAE and PUE in Crops
Definitions and Implications
Grain crops like rice, maize, wheat and oilseed rape are essential major staple foods
(FAO
2011
) and major contributors to the global phosphorus cycle (Rose and
Wissuwa
2012
). Global P flows resulting from, for instance, the rock mineral
fertiliser trade, the global grain trade or manure-delivering livestock production
