Agriculture Reference
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loci are liked to genes associated with vernalization requirements including
flowering time and shoot morphology (Su et al.
2006
). Hammond et al. (
2009
)
reported that QTLs associated with PUE measures were related to root traits in
B. oleracea
species which puts them back in the focus as potential targets for crop
improvement. QTLs for root hair length and lateral root growth have been identified
in maize under P deficiency, a trait which was observed in previous studies as
associated with improved low P tolerance and may be controlled by many minor
genes or loci with epistatic effects (Zhu et al.
2005a
,
b
). An additional study on
soybean possibly related root traits and P efficiency traits to three QTL clusters
(Liang et al.
2010
). As previously mentioned, a major storage form of phosphorus
in grain crops is the non-desirable phytate, which diminishes nutritional quality and
causes environmental problems. Despite being of strong interest for human health,
QTL analysis focusing on seed traits or seed quality has not been performed
extensively. Ding et al. (
2012
) observed an overlap of a P efficiency QTL with a
QTL for seed P concentrations and in a RIL population (durum wheat x wild emmer
wheat) and eight QTLs found for grain P content co-localised with QTLs for grain
protein content (Peleg et al.
2009
) which is correlated with both phytic acid and
total P (Raboy et al.
2009
). Zhu et al. (
2005a
,
b
) found seed phosphorus reserve-
related QTLs in maize, which was only partly related to seed size. In rice grown
with unlimited nutrients, Stangoulis et al. (
2007
) found a common QTL for phytate
and P concentrations and interestingly, the phytate QTLs were distinct from those
for micronutrients such as Fe, Zn or Mn.
So far, the underlying genes or their functional mechanisms, which are targeting
a higher low P tolerance, remain still quite elusive (Pariasca-Tanaka et al.
2009
;
Chin et al.
2010
; Shi et al.
2013
). The region of a major QTL for low P tolerance in a
rice cultivar,
Pup1 (Phosphate uptake 1),
has been mapped and has been predicted
to contains 60 genes. However, their mechanism for low P tolerance as not yet been
identified (Ismail et al.
2007
; Wissuwa et al.
2002
). In one case, the receptor-like
cytoplasmic Ser/Thr protein kinase PSTOL1 gene, present within the
Pup1
QTL
region, seems to be involved in early crown root development and enhances yield
and gene expression of such related to root growth when it was over-expressed
(Gamuyao et al.
2012
). Another approach for delivering putative candidate targets
used a comparative mapping technique (
in silico
mapping) between the model plant
Arabidopsis
and the crop
Brassica napus
(Yang et al.
2010
; Ding et al.
2012
; Shi
et al.
2013
) which revealed yield associated QTLs being linked to genes which are
involved in P homeostasis including P transport, transcriptional control, phospho-
lipid and carbohydrate metabolism (Shi et al.
2013
). Among these genes were
glucose-6-phosphate transporters, BnSIZ1-A2, BnPHO1 or BnSQD2 and phos-
phate transporters (Shi et al.
2013
) as well as BnIPS2 (Ding et al.
2012
), which
therefore confirm their potential roles as targets for crop improvement. Yang
et al. (
2010
) observed a linkage of two functional gene-based markers (GBMs)
potentially usable for MAS, BnIPS2 and BnGTP1, as well as orthologous genes for
root development, auxin transport with two root morphology related QTLs.
In summary, recent approaches have proven to be a useful tool to dissect the
genetic basis of P efficiency-related traits, and have detected a large number of
