Agriculture Reference
In-Depth Information
Genes Involved in P Starvation Signalling Cascades
As discussed above, the transcription factor PHR1 seems to be a key regulator for
downstream P-responsive genes through binding to a
P
HR
1
specific
b
inding
s
equence (P1BS)
cis
-element in model plants (Bustos et al.
2010
; Rubio
et al.
2001
). In
Brassica napus
, the homologue BnPHR1 was predominantly
expressed in the roots exposed to P limitation and over-expression enhanced
remarkably the expression of the high-affinity transporter BnPT2 (Ren
et al.
2012a
,
b
). In wheat, three PHR1 homologues genes have been identified
(Wang et al.
2013
), which regulate genes such as TaPt2;1 (Tittarelli et al
2007
; Guo
et al.
2013
) or TaIPS1 (Oono et al.
2013
) that have been reported to contain the
P1BS element. TaPht1-A1 transcriptionally activated the expression of the phos-
phate transporter TaPht1;2 in yeast cells (Wang et al.
2013
). The promoter of the
high-affinity transporter TaPht1;2 was more abundant in a P-efficient genotype than
in an inefficient genotype (Miao et al.
2009
). Furthermore, TaPHR1-A1 over-
expression resulted in an up-regulation of P starvation response genes, stimulated
lateral root branching, enhanced P uptake and P translocation and increased grain
yield but not P distribution from shoot to the grains in pot and field trials under P
deficient conditions (Wang et al.
2013
). Pht1 transporter expression of TaPht1;2 in
the roots and TaPht1;6 expression in the shoots increased under high and low P
conditions, whereas other usually P starvation induced genes such as TaIPS1.2,
TaPHO or TaSPX3 did not change their level of expression (Wang et al.
2013
).
These results indicated that TaPHR1 is an upstream regulator for Pht1 transporter
but suggested other transcriptional factors being relevant for the induction of other
P starvation induced genes as it is the case for OsPHR2 (Zhou et al.
2008
). Oono
et al. (
2013
) recently published a transcriptome study using
de novo
transcript
assembly analysis, in order to investigate wheat seedlings, cv. Chinese spring,
exposed to 10 days of P starvation. Genes of the phosphorylation category including
protein kinases were among the up-regulated transcripts (Oono et al.
2013
). Fur-
thermore, genes belonging to oxidation-reduction processes, metabolic processes,
carbohydrate metabolism, transcription process, lipid metabolism and transmem-
brane transport were induced, as well as AtWRKY6 and AtPHO1 homologues
(Oono et al.
2013
).
Rice-orthologous transcripts of PHR1, PHO2 and SIZ1 were detected but not all
were highly responsive to P starvation (Oono et al.
2011
,
2013
). Significant was the
induction of TaIPS1 homologous (Oono et al.
2013
), suggesting that the
IPS-mediated signalling cascade may also be functional as previously observed in
model species including rice (Oono et al.
2011
). This aspect is relevant when taking
in account that genetic variation in PUE of barley exhibited a correlated expression
of the low-affinity phosphate transporters, HvPht1;3 and HvPht1;6, with HvIPS1
expression (Huang et al.
2011
). Higher PUE was also a consequence of higher root-
shoot ratios under P limitation indicating an increase in carbohydrate partitioning
(Huang et al.
2011
). In model plants, IPS genes have been shown to be a
miRNA399 antagonist and involved in the miR399-PHO2 regulatory loop
