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

Grain α-amylase presents an apparent paradox for the wheat community. Despite the necessity of α-amylase for the seed germination process, high levels of amylase activity in the grain are considered detrimental for grain quality. Wheat α-amylases (EC 3.2.1.1) are endohydrolases belonging to the GH13_6 subfamily, one of the most studied subclasses of glycoside hydrolase (GH) family GH13. However, no comprehensive study had been done so far to describe and catalogue all the wheat α-amylase isoforms, despite compelling information on the involvement of two α-amylases on economically important issues for the international cereal community, namely pre-harvest sprouting and late maturity α-amylase. This study describes for the first time the genomic localization, nucleotide and amino acid sequences, phylogeny and expression profile of all known α-amylases in wheat, including a hitherto unknown fourth isoform here designated as TaAMY4. Isoform profiling strongly suggested α-amylases to be working in partnership to achieve complete degradation of a starch granule, whereas expression profiling revealed a potential involvement of TaAMY4 in the late maturity α-amylase problem.