Agriculture Reference
In-Depth Information
(Franco-Zorrilla et al.
2007
; Doerner
2008
). In wheat, TaIPS1 transcript levels were
strongly repressed in roots and TaIPS2 transcript levels in shoots of P-deficient
wheat by N deficiency (Li et al.
2008a
,
b
) providing evidence of an influence on the
signalling pathways of P homeostasis by the nitrogen nutritional status. Further-
more, nine wheat miRNAs were identified in addition to miRNA399 as responsive
to P starvation in a variety-dependent manner (Zhao et al.
2013
). TamiRNAs
putatively target diverse gene families, which are down-regulated during P defi-
ciency stress including transcriptional regulation, signal transduction, phytohor-
mone and defence responses among several others (Zhao et al.
2013
). Transgenic
tomato lines over-expressing miRNA399 from
Arabidopsis
enhanced the secretion
of acid phosphatases and protons in roots (Gao et al.
2010
). A further example is the
over-expression of another P starvation-induced transcription factor, OsPTF1 in
rice, which increased tiller number, shoot biomass, panicle weight and P content
under low Pi conditions (Yi et al.
2005
). Genes which are regulated by OsPTF1
contain E-box and G-box elements but do not include high affinity transporters or
acid phosphatases (Yi et al.
2005
). In addition, total root length and root surface
area may be increased resulting in higher P uptake rates (Yi et al.
2005
). Both
studies provide evidence of a promising method enhancing P uptake in crops
although enhancing low P tolerance via this pathway needs more understanding
of other involved proteins and factors.
Quantitative Trait Loci Identification
Until now, the indirect approach of QTL identification for P deficiency tolerance
has been mostly exploited in rice and
Brassica
species, and approaches have
focused on P acquisition parameters among different aspects and targets of P
efficiency. To date,
Pup1
(
Phosphorus uptake 1
) is the only major QTL for P
deficiency tolerance in rice coming from a landrace, which could actually be used
by rice breeders for marker-assisted introgression into elite material (Wissuwa and
Ae
2001
, Wissuwa et al.
2002
; Chin et al.
2010
).
There are more known QTLs, often at very early growth stages (Su et al.
2006
,
2009
;Yangetal.
2010
,
2011
), related to yield components under low P conditions
(Su et al.
2009
;Chinetal.
2010
;Dingetal.
2012
; Gamuyao et al.
2012
;Shi
et al.
2013
), to seed P concentrations (Ding et al.
2010
;Zhaoetal.
2008
), to P uptake
capability and morphological adaptation e.g. tiller number (Su et al.
2006
;Wissuwa
et al.
1998
,
2002
;Chinetal.
2010
; Gamuyao et al.
2012
)orrootmorphology(Zhu
et al.
2005a
,
b
,
2006
; Liang et al.
2010
; Yang et al
2011
).
In wheat, a large number of QTLs on all chromosomes have been detected in a
double haploid (DH) population derived from a P deficiency tolerant and low
P-sensitive variety implying a polygenetic control of low P sensitivity
(Su et al.
2006
,
2009
). There were three major loci associated with higher tiller
number, shoot dry weight and shoot phosphate uptake under low P conditions
suggesting that these alleles may be used for MAS (Su et al.
2006
). Two of these
