Biology Reference
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6,000 DNA markers have been developed in the
Arachis spp. (Pandey et al. 2011), for example,
random amplified polymorphic DNA (RAPD)
(Garcia et al. 1996); amplified fragment length
polymorphisms (AFLP) (Giemens et al. 2002);
inter simple sequence repeat polymorphisms
(ISSR) (Raina et al. 2001); restriction frag-
ment length polymorphisms (RFLP) (Halward
et al. 1993; Burow et al. 2001); simple sequence
repeats (SSRs) derived from genomic libraries
(He et al. 2003; Moretzsohn et al. 2003; Ferguson
et al. 2004; Moretzsohn et al. 2005; Naito et al.
2008); and sequences of expressed sequence tags
(ESTs) (Proite et al. 2007; Koilkonda et al. 2011),
and bacterial artificial chromosome (BAC)-end
sequences (Wang et al. 2012). Recently, a total
of 504 AhMITE1 transposon insertion polymor-
phic markers (hereafter referred to as transposon
markers) were also developed in peanut (Shira-
sawa et al. 2012).
Many linkage maps have been constructed
from diploid wild and cultivated species, in
addition to integrated maps based on cultivated
peanut species (Halward et al. 1993; Moretzsohn
et al. 2005; Leal-Bertioli et al. 2009; Moretzsohn
et al. 2009; Varshney et al. 2009; Khedikar et al.
2010; Hong et al. 2010; Gautami et al. 2011; Qin
et al. 2011; Sujay et al. 2011; Wang et al. 2012).
Although a number of studies have attempted
to develop DNA markers and genetic linkage
maps for peanut, the linkage groups in the lat-
est maps have not yet converged with the num-
ber of chromosome pairs (20), which suggests
that the current DNA marker resources remain
insufficient in the molecular genetics of peanut.
Recently, the International Peanut Genome Ini-
tiative (IPGI) was created and began research on
the peanut genome project. It is expected that
the activity of the peanut genome project will
accelerate advances in the molecular breeding
and genetics of peanut.
In marker-assisted selection (MAS), markers
showing linkage with targeted traits were used
for the selection of favorable individuals from
breeding populations. Such markers (hereafter
referred to as selection markers) can be devel-
oped through two approaches: (1) quantitative
trait loci (QTL) mapping, and (2) the candidate
gene approach. Several studies of QTL mapping
in peanut are published, and the most frequent
target in this field has been drought tolerance
(Varshney et al. 2009; Khedikar et al. 2010; Gau-
tami et al. 2011; Ravi et al. 2011). According
to the results of several studies, drought toler-
ance is controlled by multiple QTLs, and no
major QTL exists. Therefore, further studies are
required before MAS can be applied for the
development of selection markers for drought
tolerance. Unlike drought tolerance, major QTLs
were identified for biotic stress tolerance, in par-
ticular, late leaf spot (Sujay et al. 2011) and
tomato spotted wilt virus (Qin et al. 2011), which
showed maximum phenotypic variance of 83.0%
and 35.8%, respectively. The QTLs identified
for these two disease resistance traits could be
applied for MAS in peanut.
With respect to the use of a candidate gene
approach for the development of selection mark-
ers, genes related to the O/L ratio have been
well studied in peanut. In higher plants, oleic
acid is synthesized from stearic acid and is con-
verted to linoleic acid in a reaction catalyzed by
two fatty acid desaturases encoded by the SAD
and FA D 2 genes (Yin and Cui 2006; Clemente
and Cahoon 2009). When the FA D 2 genes from
the commonly cultivated peanut and a high-
oleate mutant that contains
80% oleate and 2%
linoleate in seed oil were compared, the high-
oleate phenotype was found to be caused by a
single nucleotide insertion (Lopez et al. 2000;
Lopez et al. 2002; Yu et al. 2008). Moreover,
the acyl carrier protein (ACP) is a central cofac-
tor for de novo fatty acid synthesis, carrying the
nascent acyl chains during the synthesis of acyl
groups. Five different types of ACP genes were
also cloned from peanut (Li et al. 2010).
As the O/L ratio is a key determinant of oil and
nutritional quality, the selection of mutated alle-
les of FA D 2 , which is associated with oleic acid
content in seeds (Martin and Rinne 1986; Garces
and Mancha 1991; Lee and Guerra 1994), is a
simple strategy to generate high-oleic acid crops
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