Molecular cloning and characterization of four novel LMW glutenin subunit genes from Aegilops longissima, Triticum dicoccoides and T. zhukovskyi

摘要

Wheat bread-making quality is largely determined by seed storage proteins present in the endosperm of the grain (Shewry and Halford 2002). The gliadins and glutenins are major seed storage proteins, which determine dough extensibility and elasticity (Payne 1987). Glutenins consist of high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits (GS), which are held together by inter- and intra-molecular disulphide bonds to form the glutenin macropolymer. The HMW-GS represent approximately 10% of the total seed storage proteins and their functions have been well established (Shewry et al. 1992, 1995). The LMW-GS account for 40% of wheat gluten and 60% of glutenins. Increasing evidence showed that these proteins significantly affect dough-quality characteristics (Gupta et al. 1989, 1991; Pogna et al. 1990; Nieto-Taladriz et al. 1994; Sissons et al. 1998; Tanaka et al. 2005), which are important for bread-making.The coding genes of LMW-GS are located at Glu-A3, Glu-B3 and Glu-D3 loci on the short arms of chromosome 1 and 6 groups (D'Ovidio and Masci 2004). According to their electrophoretic mobility in SDS-PAGE and their isoelectric points (Jackson et al. 1983), LMW-GS are classically subdivided into B, C and D groups. So far, three types of typical LMW glutenin subunits have been found based on the first amino acid residue of N-terminal sequences, viz. LMW-m, LMW-s and LMW-i types with respective methionine, serine and isoleucine as the first amino acid residue of N-terminal (D'Ovidio and Masci 2004). The LMW-s type subunits seem to be predominant (Shewry et al. 1983; Lee et al. 1999). It was found that two allelic groups detected in durum wheat, designated as LMW-1 and LMW-2, were related to poor and superior quality characteristics, respectively (Pogna et al. 1990). Relationship between LMW-GS and quality attributes in wheat has been studied and used for quality improvement of bread wheat (Ma et al. 2005).In the past fifteen years, different LMW-GS genes have been isolated and characterized in bread wheat (D'Ovidio et al. 1992; Van Campenhout et al. 1995; Masci et al. 1998; Cassidy et al. 1998; Cloutier et al. 2001; Ikeda et al. 2002; Zhao et al. 2006, 2007) and some related species (D'Ovidio and Masci 2004). The first complete LMW glutenin subunit gene was separated by PCR from durum cultivar Lira (D'Ovidio et al. 1992). Ikeda et al. (2002) isolated several LMW-GS genes from a soft wheat cultivar and classified them into 12 groups based on the N- and C-terminal sequences. More recently, some studies have focused on the characterization of LMW-GS genes from related species, including Ae. tauschii (Johal et al. 2004; Pei et al. 2007), cultivated einkorn (Lee et al. 1999; An et al. 2006), Agropyron elongatum (Luo et al. 2005), Triticum dicoccoides (Li et al. 2007) and durum wheat (D'Ovidio et al. 1997, 1999). In this paper, we isolated and characterized four novel LMW-GS genes, one each from Aegilops longissima (2n=2x=14, SlSl) and Triticum dicoccoides (2n=4x=28, AABB) and two from Triticum zhukovskyi (2n=6x=42, AmAmAAGG) respectively which shall provide new gluten gene resources and insights into the origin and evolution of LMW-GS gene family in Triticum species.