Genetic Diversity of Null Alleles of Waxy Gene in Triticum L.
In order to exploit new genetic resources for the improving of starch quality
of common wheat, the genetic diversity of null alleles of Granule-bound starch
synthase I (waxy gene) was investigated by special PCR molecular markers
in Triticum L. The results indicated that there was relative abundant
genetic diversity of waxy alleles in all accessions. Accession AS2347,
AS2356, AS2317 and AS2308 with null allele at Waxy-B1 locus and AS2310
and AS2335 with null alleles at Waxy-A1 and Waxy-B1, were observed
in 81 landraces of Triticum turdigum L. from China. In 53 landraces of
Triticum aestivum L. from Sichuan, China, eight accessions at Waxy-A1,
Waxy-B1 and Waxy-D1 loci and accession AS1668 at Waxy-D1,
were observed null alleles. In 29 Triticum macha, Accession PI361862
and PI572911 at three Waxy loci, PI572913 at Waxy-B1 and Waxy-D1,
PI572910 at Waxy-A1 and Waxy-D1, PI 290507 at Waxy-B1 and
PI572906 at Waxy-D1, respectively, were observed null alleles. Seven
accessions with null alleles at Waxy-B1 locus was observed in 28 Triticum
sphaerococcum. Specially, the accessions of two regions, Anyue in Sichuan,
China and Georgia, had the high frequency of the mutations with null alleles
of waxy gene. Landraces of Triticum aestivum L. with the high
frequency of waxy wheat, could be considered as a unique genetic resource
for improving of waxy wheat. These result suggested that the special molecular
marker could be used reliably in evaluation of genetic resources and these mutations
also could be directly used in the improving of common wheat.
Received: February 17, 2013;
Accepted: March 13, 2013;
Published: June 21, 2013
Starch, accounts for 80% of wheat grain endosperm, is one of the most important
components of cereal production (Hurkman et al.,
2003). Starch is composed of amylose (20-30%) and amylopectin (70-80%) in
cereal. The processing of starch synthesis includes three stages: the produce
of ADPG, synthesis of amylose, synthesis of amylopectin (Martin
and Smith, 1995). Granule-bound starch synthase I (GBSSI or WAXY protein)
play a key role in synthesis of amylose in endosperm tissues of cereals (Shure
et al., 1983). In wheat, GBSSI proteins were encoded by three genes:
Wx-A1, Wx-B1 and Wx-D1, located on chromosome 7AS, 4AL
and 7DS, respectively (Nakarnura, 1993). Either lack
of GBSSI activity or absence of GBSSI protein at three loci will affect the
quantitative and quality of amylose and further affect the quality of wheat
product. Especially, the null allele of Wx-B1 has the most effect for
amylase form of wheat, following Wx-D1 and Wx-A1 (Miura
and Sugawara, 1996). There are eight types for null alleles of three Wx
loci in wheat: the first type with all three alleles has 20-25% amylose content
and the second to the seventh type with any one or two null alleles decreased
the 1.7-5.0% amylose and the eighth type with three null alleles at three Wx
loci lead to very less amylose content in wheat endosperm (Nakamura
et al., 2002). Common wheat with partial null alleles at Wx
loci, which lacks one or two WAXY proteins, have been identified widely, but
the mutation with three null alleles at Wx loci in natural genetic resources
was very less mentioned (Yamamori et al., 1998;
Wang et al., 1999). Lacking all three WAXY proteins
from three Wx loci could produce the waxy wheat (Nakamura
et al., 1995). Through crossing the materials of Kanto 107 (null
allele at Wx-A1 and Wx-B1 loci) and Baihuomiao (null allele at
Wx-D1), the mutation has been generated with the entire null allele at
three Waxy loci. Amylose content of this waxy wheat is 0.6-0.7% (Nakamura
et al., 1993a, b, 1995).
Otherwise, the starch characters and potential end use of waxy wheat have been
reported (Lee et al., 2001; Bhattacharya
et al., 2002).
The types of waxy proteins could be identified by 1D-SDS-PAGE (Zhao
and Sharp, 1996) but the manipulation is complex and the endosperm of wheat
is also damaged in the process of prepare sample. Molecular markers were also
developed following know the sequence information of waxy gene in wheat (Ren
et al., 2004). Using molecular marker could not only overcome the
limitation of protein electrophoresis, but also detect easily in any stages
of wheat development. Molecular assisted selection (MAS) of waxy gene
can accelerate the improving of way wheat and wheat production. Three molecular
marker of waxy gene had been applied in the breeding of waxy wheat in
Austria (McLauchlan et al., 2001) and an improved
method by one simple Polymerase Chain Reaction (PCR) to identify three Wx
loci was also reported (Nakamura et al., 2002).
In the present study, the allele component of Waxy gene was investigated in landraces of Triticum aestivum L. (AABBDD, 2n = 42) from Sichuan, China, landraces of Triticum turgidum L. (AABB, 2n = 28) from China, Triticum macha Dekapr. et Menabde(AABBDD, 2n = 42) and Triticum sphaerococcum Perc. (AABBDD, 2n = 42) by special molecular marker. The results could help us to understanding the diversity of waxy gene in these genetic resources and exploiting new genetic materials to use in breeding of common wheat.
MATERIALS AND METHODS
Materials: A total of 81 accessions of T. turgidum L. landraces from China, 53 accession of T. aestivum L. landraces from Sichuan, China, 29 accessions of T. macha and 28 accessions of T. sphaerococcum, were used in this study (Table 1). The materials with AS were provided by the Germplasm Laboratory of Triticeae Research Institute, Sichuan Agriculture University and the other materials were kindly provided by Dr. Harold Bockelaman, USDA-ARS, National Small Grains Collection.
Methods: All seeds were germinated under the dark at 23 for 1 week,
young leaves were harvested and crushed into powder with the aid of liquid nitrogen
and the genomic DNA extracted by the CTAB method (Wang
et al., 2008). A pair of primers, derived from the exon 4/6 region of
the GBSSI gene (McLauchlan et al., 2001), was
used as the special molecular markers. The forward primer: 5-AAG AGC AAC
TAC CAG T-3 is located in exon 5 (position 1464-1481) and the reverse
|| Materials used in this study
5-TCG TAC CC G TCG ATG AAG TCG A-3 is located in exon 6(1508-1530)
(Yan et al., 2000). PCR was performed in a 50
μL volume, containing 1.5 UTaq plus DNA polymerase, 100 ng of each
template DNA, 5μL PCR buffer (supplied with Taq plus DNApolymerase), 1.5
mM MgCl2, 100 mM of each dNTP and 150 ng each primer. The reactions
were conducted in a PTC-220 (MJ Research, USA) using the following program:
94°C for 3 min, followed by 12 cycles at 94°C for 1 min, at 64°C
for 1 min and at 72°C for 30 sec and followed by 34 cycles at 94°C 1
min, 58°C 1 min and 72°C 30 sec and a final extension step of 72°C
for 5 min. The PCR products were separated on 3% agarose gel.
Allele variation of Waxy gene in landraces of T. turgidum
L.: Two bands could be amplified at Wx-A1 and Wx-B1 loci in
the landraces of T. turgidum L. from China (Fig.
1a). The band with bigger size came from Wx-A1 locus and the small
one from Wx-B1 locus. The different size of PCR product resulted from
the different length between the fifth exon and the sixth exon of waxy
gene. Both two bands were obtained in 75 accessions of all 81 accessions of
tetraploid landraces. No band was obtained in accession AS2310 (Nanmai, Renshou)
and AS2335 (Dabaimai, Anxi), indicated that there were null alleles at Wx-A1
and Wx-B1 loci in these two accessions. Four accessions (4.9%), AS2347
(Fushoumai, Jianhu), AS2356 (Fushoumai, Qishan), AS2317 (Zaozhuo, Batang) and
AS2308 (Wugongnanmai, Suining), were identified as the mutation with null allele
at Wx-B1 locus. These results suggested that the frequency of mutations
with null alleles at Wx loci was very lower in landraces of T.
turgidum L. from China.
||PCR assays for detection of null alleles of the waxy genes
in Triticum L. (a) Landraces of T. turgidum L., 1.
AS2236, 2. AS2239, 3. AS2240, 4. AS2310, 5.AS2311, 6. AS2312, 7. AS2313.
(b) Landraces of T. aestivum L., 1. AS1589, 2. AS1647, 3. AS1668,
4. AS1591. (c) T. macha, 1. PI572910, 2. PI572906, 3. PI361862,
4. PI572911, 5. PI272554, 6. PI272555, 7. PI290507, 8. PI572913. (d) T.
sphaerococcum, 1. PI324492, 2. PI282451, 3. AS348, 4. PI277142, 5.
PI42013, 6. PI42014, 7. PI330556
Allele variation of Waxy gene in landraces of T. aestivum
L.: Three bands were identified at Wx-A1, Wx-B1 and Wx-D1
loci in T. aestivum L. from Sichuan, China (Fig.
1b). The band with the biggest size was amplified from Wx-D1 locus
and the one with the second bigger size from Wx-A1 locus and the least
band from Wx-A1 locus. No bands were amplified from eight accessions
(15%) in 53 landraces of common wheat. These mutations with null alleles at
three Wx loci included AS1591 (Hongxiaomai, Anyue), AS1670 (Shihonghuamai,
Pengxian), AS1592 (Nverhong, Anyue), AS1598 (Dahongpao, Zizhong), AS1655 (Baixiaomai,
Dazhu), AS1590 (Dongmai, Anyue), AS1556 (Tuomai, Bazhong) and AS1573 (Liulengmai,
Changning). Lacking the band from Wx-D1 locus was only observed in one
accession, AS1668 (Youmangmai, Xinjing). Whole three bands were amplified from
43 accessions of landraces of common wheat. Three accessions from Anyue, Sichuan,
China, were the mutations with null alleles at three Wx loci. The results
suggested that there was abundant allele diversity of Waxy gene in landraces
of common wheat from Sichuan, China.
Allele variation of Waxy gene in T. macha: Three
bands could be obtained from 23 accessions of T. macha (Fig.
1c). No band was amplified in two accessions, PI361862 (from Danmark) and
PI572911 (from Georgia), indicated that they belonged to the mutations with
null alleles at three Wx loci. Only one band was amplified in two accessions,
PI572913 (from Georgia), which showed null alleles at Wx-B1 and Wx-D1
loci and PI572910 (from Georgia), which showed null alleles at Wx-A1
and Wx-D1 loci. Only one accession, PI290507 (from Hungary), showed the
null allele at Wx-B1 locus and one accession, PI572906 from Georgia,
had the null allele at Wx-D1 locus. Four out of six mutations with at
least one null allele at three Wx loci came from Georgia, suggested that
it was very important region for genetic resources of Waxy gene.
Allele variation of Waxy gene in T. sphaerococcum:
Three bands were amplified in 21 accessions of T. sphaerococcum
(Fig. 1d). Null allele at Wx-B1 locus was identified
in five accession from India, which including PI324492, PI282451, PI42014, PI352498
and PI282452 and two from Pakistan, which including PI40941 and PI40943. The
result suggested that there was relative simple genetic diversity of allele
of Waxy gene in T. sphaerococcum.
Very less information about natural genetic resources of common wheat with
null alleles at three Wx loci was reported (Yamamori
et al., 1998; Wang et al., 1999).
The waxy wheat with three null alleles at waxy gene locus was produced
by crossing between mutations with partial null alleles at different Wx
loci (Nakamura et al., 1993a; b
1995). In recent years, waxy wheat is becoming more
and more interesting for wheat breeders and industry, because of its unique
quality characters (Lee et al., 2001; Bhattacharya
et al., 2002). In addition, modification of cereal starch by various
methods could provide different production suitable for food and various industrial
applications (Kaur et al., 2012). Waxy
gene plays an important role in synthesis of cereal starch and its activity
directly affects the quantity and quality of starch. Thus, exploiting the new
allele of waxy gene in genetic resources of common wheat is very important
work for the improving of wheat and modification of starch. In the present study,
the allele variation was investigated in the four important genetic resources
of common wheat, landraces of T. turgidum L., landraces of T.
aestivum L., T. macha, T. sphaerococcum.
Landraces of T. turgidum L., which was grown widely in China before
the 1950s, showed the unique performance about the gliadin, HMW-glutenin,
protein content and microsatellite (Li et al., 2006a,
b). Landraces of T. aestivum L. from Sichuan,
China, also known as Sichuan White Wheat, were widely planted and
conserved by the peasants in the province ago (Liu et
al., 2005). This population is considered to be a unique resource for
genetics and breeding, because of broad hybrid compatibility with rye (Luo
et al., 1992; Liu et al., 2003).
T. macha and T. sphaerococcum were also displayed
abundant genetic diversity and contain gene resource for quality and disease
resist of wheat (Cao et al., 1998; Chen
et al., 2012).
In present study, abundant genetic diversity of alleles of Waxy gene
was observed in Triticum L. species. In tetraploid, T. turgidum
L., two accessions with null alleles at both Wx-A1 and Wx-B1 loci,
four accessions with null allele at Wx-B1 locus, suggested that there
was relative lower diversity of allele of waxy gene in this landraces.
In hexaploid, T. sphaerococcum also showed the similar performance
of alleles of waxy gene, as only null allele at Wx-B1 locus was
observed in seven accessions. Landraces of T. aestivum L. from
Sichuan, China, showed the highest percentage (15%) of null alleles at three
Wx loci. Including the mutations with null alleles at three, two and
one Wx loci, were detected in T. macha, suggested that
this hexaploid species had abundant genetic diversity of alleles of waxy
gene. Actually, this species with high genetic diversity was also observed by
RAPD (Cao et al., 1998). In addition, the mutations
with different null allele at Wx loci, which were identified now, could
be used in the improving of common wheat. The next steps for these mutations
with null alleles of waxy gene should be focus on sequence cloning and
gene expression to understanding the molecular mechanism of these null alleles.
Waxy mutations with null alleles occur spontaneously in cereals (Eriksson,
1970). Null alleles at the Wx-A1 locus have been found in samples
from Japan, Korea and Turkey, while null alleles at the Wx-B1 locus are
very common in the materials from Australia and India (Yamamori
et al., 1994, Yamamori and Endo, 1996) and
Italy (Boggini et al., 2001). Null alleles at
the Wx-D1 locus were more rarely and identified only in Baihuo (Yamamori
et al., 1994) and one Italian landrace (Boggini
et al., 2001). Wang et al. (1999)
also found one accessions with null allele at Wx-D1, six accessions with
null alleles at Wx-B1, in 900 landraces and cultivars. These results
suggested that the mutations with null alleles at Wx loci had the very
lower frequency in genetic resources. In our results, all the accessions still
showed the relative lower percentage of null alleles of waxy gene. In
a total of 191 accessions, only two hexaploid accessions showed null alleles
at both two Wx loci and 12 accessions showed null alleles at Wx-B1
locus and two accessions showed null alleles at Wx-D1 locus. But the
mutations with null alleles at three Wx loci had higher percentage, especially
in landraces of T. aestivum L. from Sichuan, China (15%), suggested
that this landraces population is unique genetic resource for improving of waxy
wheat. The reason that the landraces had high frequency of null alleles could
be related with the special dietetic habit of people living in Sichuan.
The usual method to breeding waxy wheat is to crossing these materials with
different null alleles of Waxy gene (Yamamori et
al., 1995; Urbano et al., 2002). Now
10 accessions with null alleles at three Wx loci were identified from
Triticum L. genetic resources. All the mutations could be directly used
in breeding of common wheat and save the time of selection. Furthermore, the
variation of Waxy gene was only investigated at DNA level. The performance
of amylose and starch and the quality in these mutation materials should be
further investigated. The influence of the variation of Waxy gene loci
for the amylose and the relating quality characters also should be focused in
Identifying null allele types of waxy gene of the materials is very
important for the breeding of waxy wheat. The main methods for waxy gene
expressing included measuring the amylose content, swelling power, RVA pasting
characteristics, iodine staining and waxy protein electrophoresis (Nakamura
et al., 1993a, b ;Crosbie,
1991; McCormick et al., 1994; Sulaiman
and Morrison, 1990). Zhao and Sharp (1996) improved
the 1D-SDS-PAGE method and can easy identify three WAXY protein and suggested
that this method could be used in wheat breeding. Wang
et al. (1999, 2000) further improved SDS-PAGE
method and could identify four WAXY subunits (Wx-A1, Wx-E1, Wx-D1
and Wx-B1). Pan et al. (2000) also used
the 2D-SDS-PAGE to distinguish WAXY protein. But SDS-PAGE method is difficult
to apply widely in breeding of wheat, because the process of preparative of
samples and manipulation process is very complex and lower effective. The molecular
marker method based on PCR was applied widely after the cDNA sequence of Waxy
gene reported. Shariflou and Sharp (1999) designed
SSR primers to identify the Wx-D1 locus and Briney
et al. (1998) designed STS-PCR primers to identify the Wx-B1
locus. Nakamura et al. (2002) confirm that the
PCR markers could identify the waxy wheat with different null alleles
at Wx loci and McLauchlan et al. (2001) reported
that the special PCR markers, which could identify null alleles of waxy gene,
were applied in Australian wheat breeding program. The present study also further
confirmed that these molecular markers also could be used reliably in evaluation
of genetic resources of Triticum L.
In this study, the mutations with null alleles at Wx loci were identified in landraces of T. turgidum L. from China, landraces of T. aestivum L. from Sichuan, China, T. macha and T. sphaerococcum, by one pair of specific primer. In all 191 accessions, only two hexaploid accessions showed null alleles at both two Wx loci and 12 accessions showed null alleles at Wx-B1 locus and two accessions showed null alleles at Wx-D1 locus. Interestingly, 10 hexaploid accessions with null alleles at three Wx loci and two tetraploid accessions with null alleles at two Wx loci, were observed. The mutations with null alleles of Waxy gene were easily obtained in the accessions from Anyue, Sichuan, China and from Georgia. Landraces of T. aestivum L. from Sichuan, China, is unique genetic resource for improving of waxy wheat, because of the high frequency of waxy wheat. The reason could be related with the special dietetic habit of people living in this region. Further research could help to deeply understand the performance of these mutations about sequence variation, gene expression and quality. These result suggested that the special molecular markers could be used reliably in evaluation of genetic resources and these mutations also could be used directly in the improving of common wheat.
This study was supported by the National Basic Research Program of China (973 Program and 2011CB100100) and the National Basic Research Special Program of China (Grant No. 2010CB134402).
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