Genetic, Hormonal, and Physiological Analysis of Late Maturity α-Amylase in Wheat    

Abstract

Late maturity a-amylase (LMA) is a genetic defect that is commonly found in bread wheat (Triticum aestivum) cultivars and can result in commercially unacceptably high levels of a-amylase in harvest-ripe grain in the absence of rain or preharvest sprouting. This defect represents a serious problem for wheat farmers, and apart from the circumstantial evidence that gibberellins are somehow involved in the expression of LMA, the mechanisms or genes underlying LMA are unknown. In this work, we use a doubled haploid population segregating for constitutive LMA to physiologically analyze the appearance of LMA during grain development and to profile the transcriptomic and hormonal changes associated with this phenomenon. Our results show that LMA is a consequence of a very narrow and transitory peak of expression of genes encoding high-isoelectric point a-amylase during grain development and that the LMA phenotype seems to be a partial or incomplete gibberellin response emerging from a strongly altered hormonal environment.

New insight in cereal starch degradation: identification and structural characterization of four α-amylases in bread wheat

“…The tertiary structure of four representatives of each wheat α-amylase isoform were modelled and the results confirmed both the fold and domain arrangement typical for family GH13 members [5]: (i) the catalytic (β/α) 8 -barrel domain; (ii) domain B protruding out from the barrel between the strand β3 and helix α3; and (iii) domain C succeeding the barrel (Figure 3). Although they all most resemble the structures of both barley α-amylase isozymes [10,48], the structure of the low pI isozyme (Figure 3a) was used for comparison.…”

“…In agreement with the CAZy classification [51], the two GH13 subfamilies are clearly separated from each other. Within the two subfamilies also the α-amylases originating from two different taxa are clustered separately (plant vs. bacteria for GH13_6 and archaeons vs. bacteria for GH13_7) reflecting also subtle Overall structures shown as solid ribbon models signifying catalytic (β/α) 8 -barrel domain (blue), domain B (red) and domain C (green) protruding out of and succeeding, respectively, the barrel domain. (a) Barley low pI α-amylase isozyme AMY1 complexed with its substrate analogue thio-DP4 (PDB code: 1P6W; [10]).…”

“…The overall protein structure is representative of the GH13_6 family corresponding to the α-amylase from the plant kingdom (for a review, see [29]) (Figure 1). TaAMY4 presents a secreting peptide (Gly2-Arg24), a main catalytic domain (domain A including the domain B) with a (β/α) 8 -barrel fold (Leu28-Leu376) and a C-terminal domain C adopting an antiparallel β-sheet structure (Arg366-Lys426). TaAMY4 showed ten residues potentially involved in the active site, three catalytic residues and two calcium binding site residues characteristic of the subfamily GH13_6 (Figure 1).…”

“…The evolutionary tree was based on the alignment (including the gaps) of the sequence segment spanning almost the entire catalytic (β/α) 8 -barrel domain including the domain B from the beginning of the strand β1 (the region 8_FNW in the barley low pI α-amylase isozyme; UniProt accession No. : P00693; [35]) to the end of the strand β8 (the region 318_GIPCIFYDH in the same enzyme).…”

“…To date, there are at least four α-amylase categories in barley, from HvAMY1 to HvAMY4, while rice shows at least ten separate genes clustered into three subfamilies (OsAMY1, OsAMY2 and OsAMY3) [6,7]. All subfamilies in barley or rice have been demonstrated to be expressed at different grain developmental stages and in various tissues [8,9]. More importantly, structure comparison of barley α-amylase isozymes 1 and 2 reveals particular features suggesting differences in sugar recognition and processing [10].…”