Biology Reference
In-Depth Information
181 (1,963 cM) marker loci, respectively, along
with construction of a consensus map based on
these two populations segregating for foliar dis-
ease resistance with 225 SSR loci and a total
map distance of 1,152.9 cM (Sujay et al. 2011).
In addition to the aforementioned three satu-
rated maps, more recently two more genetic
maps based on RIL populations segregating for
traits related to drought tolerance, namely ICGS
76
diploid map of Moretzsohn et al. (2005) to 165
SSR, 78 anchor markers, 17 RGA, and 507
SNP markers (Gouvea 2012). A second SNP-
based map of peanut has been reported by Nagy
et al. (2010), wherein a high-density genetic
map of the A genome was developed from an
intraspecies cross within
A. duranensis
, and 971
SSRs, 221 single-stranded DNA conformation
polymorphism (SSCP) markers, and 1,127 SNPs
were mapped. Extension of SNP-based maps to
the tetraploid has not been accomplished yet,
and will require separation of A- and B-genome
sequences, but is expected to greatly accelerate
genetic mapping and marker-assisted selection
when available.
×
CSMG 84-1 (119 SSR loci) and ICGS
×
44
ICGS 76 (82 SSR loci), were developed
with genome coverage of 2,208.2 cM and 831.4
cM, respectively. Since the aforementioned three
populations (TAG 24 and ICGV 86031, ICGS
76
ICGS 76)
were segregating for traits related to drought tol-
erance, a consensus map (2,840.8 cM) with 293
SSR loci was developed. All the parentals were
cultivated genotypes, except for GPBD-4, which
is predominantly cultivated with some
A. car-
denasii
parentage derived through the hexaploid
route (Smartt et al. 1978; Gowda et al. 2002).
They observed 6-10% polymorphism for dif-
ferent marker types and mapped 652 markers
into a high-density composite map based on all
the five populations. More recently, Qin et al.
(2012), after screening a total of 4,576 mark-
ers, identified 260 and 181 polymorphic mark-
ers, respectively, for the two RIL populations,
namely Tifrunner
×
CSMG 84-1, and ICGS 44
×
Resistance Gene Analogs
Plant resistance genes have been found to fall
into several classes, among which genes encod-
ing the nucleotide binding site (NBS) are the
most characterized. The NBS domain is thought
to act in signal transduction pathways.
Using conserved amino acid motifs, degen-
erate primers can be designed that are able
to amplify RGAs from any plant species (see
Hammond-Kosack and Parker 2003). Using
such primers, RGAs have been identified from
wild and cultivated peanut. Seventy-eight nonre-
dundant NBS-encoding regions were charac-
terized by Bertioli et al. (2003). Phylogenetic
analysis of these sequences with NBS encod-
ing sequences from
Arabidopsis thaliana
,
Med-
icago truncatula
,
Glycine max
,
Lotus japoni-
cus
, and
Phaseolus vulgaris
showed that most
Arachis
NBS sequences fall within legume-
specific clades, and that sequences in some
clades appear to have undergone extensive copy
number expansions in the legumes. This under-
lines the apparent quickly evolving nature of
resistance gene analogs. An additional 234
sequences were identified and mapped onto
250 nonredundant BAC clones containing NBS-
encoding sequences (Yuksel et al. 2005). More
recently, 401 RGAs were mined from a peanut
×
GT-C20 (T population) and
SunOleic 97R
NC94022 (S population). Indi-
vidual genetic maps were constructed for T and
S populations with 236 and 172 marker loci,
respectively. An integrated map was then con-
structed with 324 marker loci covering 1,352 cM
genome distance (Qin et al. 2012). For the cre-
ation of the highest-density map of cultivated
peanut to date, with more than 1,000 mark-
ers, screening was done by
in silico
analysis of
DNA sequence data from the parentals (Shira-
sawa et al. 2012).
×
SNP-Based Maps of Peanut
Two significant SNP-based maps exist for
peanut. The first is an extension of the A-genome
Search WWH ::
Custom Search