Cloning and characterization of Agp1 , the gene encoding the small subunit of ADP-glucose pyrophosphorylase from wheat and its relatives

ADP-glucose pyrophosphorylase (AGP) consists of two large (AGP-L) and two small (AGP-S) subunits; it regulates the limiting step in the biosynthesis of starch. Here, we isolated the full-length cDNA sequence of the AGP-S gene (designed as Agp1 ) from wheat and whole genomic sequences from relatives of wheat. The coding region of Agp1 ranged from 5948 bp to 7666 bp and contained 9 exons and 8 introns. The full-length cDNA sequence of Agp1 encoded a polypeptide containing 473 amino acids without transit peptides. The sequence alignment and phylogenetic tree analyses indicated that the Agp1 cDNA sequence was highly conserved (99.7%) across the diploid Triticeae species examined in this study. Variations in introns caused the Agp1 genomic sequences from wheat relatives to be less similar (79.5%), and Agp1 sequences from the B genome donor species were divergent. In developing grains, rapid increase in Agp1 expression at prophase was closely followed by the accumulation of starch, and a significant ( P < 0.001) correlation was observed between them. The heterogeneous mixtures of small and large subunits from different wheat species restarted glycogen synthesis in the Escherichia coli AC70R1-504 cells, which are deficient in endogenous AGP activity ( glg C -/- ). Our data provide useful information to evaluate and utilize Agp1 sequences in Triticeae species.