Molecular characterization and sequence diversity of genes encoding the large subunit of the ADP-glucose pyrophosphorylase in wheat (Triticum aestivum L.)

Abstract

The large subunit of ADP glucose pyrophosphorylase (AGPase), the rate limiting enzyme in starch biosynthesis in Triticum aestivum L., is encoded by the ADP glucose pyrophosphorylase large subunit (AGP-L) gene. This was the first report on the development of three genome-specific primer sets for isolating the complete genomic sequence of all three homoeologous AGP-L genes on group 1 chromosomes. All three AGP-L genes consisted of 15 introns and 15 exons. The lengths of the structural genes from start to stop codon were 3334 bp for AGP-L-A1, 3351 bp for AGP-L-B1, and 3340 bp for AGP-L-D1. The coding region was 1569 bases long in all three genomes. All three AGP-L genes encoded 522 amino acid residues including the transit peptide sequences with 62 amino acid residues and the mature protein with 460 amino acid residues. The mature protein of three AGP-L genes was highly conserved. Three AGP-L genes were sequenced in 47 diverse spring and winter wheat genotypes. One and two haplotypes were found for AGP-L-D1 and AGP-L-A1, respectively. In total, 67 SNPs (single nucleotide polymorphisms) and 13 indels (insertions or deletions) forming five haplotypes were identified for AGP-L-B1. All 13 indels and 58 of the 67 SNPs among the 47 genotypes were located in the non-coding regions, while the remaining nine SNPs were synonymous substitutions in the coding region. Significant LD was found among the 45 SNPs and ten indels located from intron 2 to intron 3. Association analysis indicated that four SNPs were strongly associated with seed number per spike and thousand kernel weight.

Final grain weight is not limited by the activity of key starch-synthesising enzymes during grain filling in wheat

“…These results are at odds with the widespread expectation that high AGPase activity in the endosperm leads to high starch content and hence high grain weight (discussed in Tuncel and Okita, 2013 ; Cakir et al , 2015 ), and with previous research that supports this expectation. For example, transgenic wheat with elevated AGPase activity in the grain has higher final grain weight than untransformed controls ( Kang et al , 2013 a ), and polymorphisms in genes encoding the subunits of AGPase have been associated with variation in final grain weight in two different panels of wheat genotypes ( Rose et al , 2016 ; Hou et al , 2017 ). We suggest that these effects of AGPase variation on grain weight may not arise during grain filling, but may instead reflect a crucial role for the enzyme in events around the time of anthesis that influence final grain weight via the extent of expansion of enclosing maternal tissues or patterns of endosperm cellularisation.…”

“…Specifically, transgenic wheat plants with elevated AGPase activity during grain filling have been reported to have both more grains and higher yields ( Smidansky et al , 2002 ; Kang et al , 2013 a ), and in one case higher individual seed weight ( Kang et al , 2013 a ). Haplotypes of genes encoding both the large and the small subunits of AGPase are also reported to show association with wheat grain weight ( Rose et al , 2016 ; Hou et al , 2017 ). Indirect evidence for the importance of AGPase comes from experiments in which developing wheat ears were treated with a chemical from which the sugar-signalling molecule trehalose 6-phosphate (T6P) is released by UV light.…”

Comparative Analysis of AGPase Genes and Encoded Proteins in Eight Monocots and Three Dicots with Emphasis on Wheat

“…The genes encoding the LS were cloned from maize and hexaploid wheat (Shaw and Hannah, 1992; Thorneycroft et al, 2003; Rose et al, 2016); however, genes for the SS were cloned only from maize and potato (Nakata et al, 1994; Hannah et al, 2001). Recently, the primary and secondary structures of the AGPase subunits have been analyzed in silico in some selected monocots (maize, wheat, rice and barley) and dicots (potato and Arabidopsis ) (Rani et al, 2013), where major emphasis was laid on the study of physico-chemical properties of amino acids and their importance in conferring stability to proteins.…”

The AGPase Family Proteins in Banana: Genome-Wide Identification, Phylogeny, and Expression Analyses Reveal Their Involvement in the Development, Ripening, and Abiotic/Biotic Stress Responses

“…It was found that the large subunits harbor 14–15 exons, whereas small subunits contain significantly fewer, only 9–10 exons. Such a structural feature of MaAGPases has also been observed in other plant species, such as Triticum aestivum [ 38 ], I. batatas [ 39 ], and H. vulgare [ 40 ]. Moreover, these two types of subunits also differ in their conserved motifs ( Figure 3 ), as previously observed in T. aestivum [ 10 ].…”