Agriculture Reference
In-Depth Information
(Oono et al.
2011
). The over-production of citrate in transgenic tobacco (L
´
pez-
Bucio et al.
2000
) as well as mitochondrial citrate synthase in
A. thaliana
(Koyama
et al.
2000
) enhanced P
i
uptake. Key enzymes which have been studied in
A. thaliana
are citrate synthase, malic enzyme and aconitase, which exhibited
variation in protein abundance between ecotypes during P deficiency (Chevalier
and Rossignol 2011). In other species, the activity of aconitase correlated with
organic acid secretion (Neumann and R
¨
mheld
1999
) and in alfalfa, the
overexpression of malate dehydrogenase (MDH) resulted in increased P accumu-
lation (Tesfaye et al.
2001
). Another approach was the expression of phytase genes
of alfalfa or of a fungal origin in
Arabidopsis
and tobacco plants, resulting in
improved acquisition of organic P sources (George et al.
2005
). However, the
length of P starvation influences the synthesis and degradations of proteins which
are potentially involved in enhancing the plants adaptation to P deficiency. For
instance, genes encoding for isocitrate dehydrogenase were suppressed in rice roots
only after a certain time of exposure to P starvation, resulting in a suppression of
citrate degradation (Oono et al.
2011
).
The replacement of phospholipids by galactolipids or sulpholipids is a well-
known adaptation process in plants during P deficiency (Andersson et al.
2003
;
Hammond et al.
2003
; Byrne et al.
2011
), even if phospholipid degradation is
differently mediated in different species (Calder´n-V´zquez et al.
2011
). For
instance, in potato, an array study identified novel roles for the main storage protein
in potato tubers, the patatin-like proteins, which also have lipase activity and are
potentially involved breakdown of phospholipids for P
i
recycling (Hammond
et al.
2011
). Numerous studies in model plants or crops reported the induction of
genes related to an altered lipid metabolism, for example UDP-sulfoquinovose
synthase 1 (SQD1) or glycerophosphoryl diester phosphodiesterase (GDPD) or
lipid transfer proteins (Hammond et al.
2011
; Oono et al.
2011
; Morcuende
et al.
2007
; Calder
´
n-V
´
zquez et al.
2008
; Wasaki et al.
2003
). Glyceropho-
sphodiester phosphodiesterases (GPX-PDE) catalyse the hydrolysis of phospho-
lipids to glycerol-3-phosphate and the corresponding alcohol. Recently, GPX-PDE
genes were identified which were highly expressed in cluster roots of white lupine
under P
i
-deficiency (Cheng et al.
2011
; Uhde-Stone et al.
2003
).
To date, the knowledge about functional consequences of replacing phospho-
lipids in membranes is very limited (Veneklaas et al.
2012
).
Post-translational Modifications
Post-translational modifications are important factors in P signalling and metabolic
pathways involved in PUE (Alexova and Millar
2013
; Plaxton and Tran
2011
),
highlighted when comparing proteome with transcriptome studies in P-starved
maize (Calder´n-V´zquez et al.
2008
; Li et al.
2008a
,
b
) and
Arabidopsis
(Morcuende et al.
2007
). A striking example underpinning the importance of
post-translational modifications within adaptation to low P exposure is the potential