Page 6 - Molecular Plant Breeding

Molecular Plant Breeding 2011, Vol.2, No.9, 60 -67
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61
al., 1997; Ball et al., 1998; Hirose and Terao, 2004).
The granule-bound starch synthase family (GBSS) is
responsible for amylose synthesis and is exclusively
bound to the starch granule. The SSⅠ-Ⅲ isoforms
are involved in amylopectin biosynthesis, while the
SSⅣ isoform in the control of granule numbers (Ball
and Morell, 2003; Roldán et al., 2007).
SS isoforms have been identified in several Gramineae
genomes through amino acid homology analysis. In
rice (Oryza sativa L.), there are 10 SS isoforms
separated into five types, including two GBSS genes
(GBSS Ⅰ/WX and GBSS Ⅱ), one SS Ⅰgene, three SS
Ⅱ genes (SS Ⅱa, SS Ⅱb , and SS Ⅱc), two SSⅢ genes
(SS Ⅲa and SS Ⅲb), and two SSⅣ genes (SS Ⅳa and SS
Ⅳb) (Hirose and Terao, 2004). Compared to the rice
genome through the current data, Maize (Zea mays L.)
genome contains two SS Ⅱb and two SS Ⅲb genes, but
only one SS Ⅳgene (Yan et al., 2009). In wheat,
seven SS genes, GBSS Ⅰ/WX, GBSS Ⅱ, SS Ⅰ, SS Ⅱa,
SS Ⅱc, SS Ⅲa, and SS Ⅳb, had been cloned (Clark et
al., 1991; Li et al., 1999a, 1999b, 2000; Leterrier et al.,
2008; Yan et al., 2009).
In this study, we reported the cloning and
characterization of the genes encoding GBSS, SS Ⅰ,
SS Ⅱ, SS Ⅲand SS Ⅳin sorghum, and the SS Ⅱb and
SS Ⅲb genes in wheat. We found that the duplicator of
SS Ⅳgene was lost in the sorghum, maize and wheat
genomes. The expression patterns of the detected SS
genes were analyzed and the evolution of the SS gene
family in Gramineae was discussed.
1 Results and Discussion
1.1 Identification of the SS genes in sorghum and
wheat
The previous studies reported the cloning of the genes
encoding GBSS Ⅰ, GBSS Ⅱ(Clark et al., 1991), SS Ⅰ
(Li et al., 1999b), SS Ⅱa (Li et al., 999a), SS Ⅱc (Yan
et al., 2009), SS Ⅲa (Li et al., 2000), SS Ⅳ(Leterrier et
al., 2008) in wheat, and GBSS Ⅰ/WX (EF089858), SS Ⅰ
(AF168786) in sorghum. In this study, we determined
the complete coding domain sequences of the other six
SS genes in sorghum and two in wheat. The
designated gene names and GenBank accession
numbers were SbGBSS Ⅱ (EF472254), SbSS Ⅱa
(EU620718), SbSS Ⅱ b (EU620719), SbSS Ⅱ c
(EU307275), SbSS Ⅲ a (EU620720), SbSS Ⅲ b
(EU620721), TaSS Ⅱb (EU333947) and TaSS Ⅲb
(EU333946). Only one SS Ⅳgene (XM_002440083)
was detected in the public sorghum genomic
sequences and EST database. No SS Ⅳa gene was
detected in wheat genomic sequences and EST
database in NCBI and the raw Chinese spring
genomic sequence reads using BLAST (http://www.
cerealsdb.uk.net/search_reads.htm). The domain orga-
nization of SS proteins in Gramineae was listed in
Table 1.
1.2 Phylogenetic relationships among the duplicated
SS genes
In order to characterize the identified SS genes in
sorghum and wheat, a phylogenetic tree was built with
58 SS amino acid sequences from some monocots and
dicots (Figure 1, a bacterium glycogen synthase,
EcGS, was as out group for the phylogenetic analysis).
The phylogenetic tree indicated that the SS proteins
are grouped into five clades of GBSS, SSⅠ , SSⅡ , SS
Ⅲ , and SSⅣ . In Gramineae, GBSS proteins were
further divided into two subisoforms of GBSS Ⅰ and
GBSSⅡ , SS Ⅱ proteins into SSⅡa, SSⅡ b and SSⅡ
c, SSⅢ proteins into SSⅢa and SSⅢb, SSⅣ proteins
into SSⅣa and SSⅣ b, respectively (Figure 1). The
present determined wheat SS Ⅱ and SSⅢ fall into the
SSⅡb and SSⅢb subisoforms, respectively (Figure 1).
The previous study found the WGD event occurred
approximately 70 million years ago (Mya) prior to the
divergence of the Gramineae (Paterson et al., 2004).
Thus, it is likely that the duplicators of GBSS, SSⅡ ,
and SSⅢb, but not SSⅣ , were retained in genomes of
the observed Gramineae species.
1.3 Alignments of syntenic regions that contain the
SS Ⅳ gene among rice, maize, and sorghum
genome
The two SS Ⅳ genes in rice were located on
chromosome 1 and chromosome 5, respectively. In
order to determine whether the SS Ⅳa gene is lost in
sorghum and maize genomes, we compared the gene
cluster on syntenic region containing the SS Ⅳgenes
among rice, sorghum, and maize, based on the
rice-maize-sorghum synteny (http://www.gramene. org/).