Molecular cloning and expression analysis of the starch-branching enzyme III gene from common wheat (Triticum aestivum ).

The starch-branching enzyme (SBE) catalyzes the formation of branch points by cleaving the α-1,4 linkage in polyglucans and reattaching the chain via an α-1,6 linkage. Three types of SBE isoforms (SBEI, SBEII, and SBEIII) exist in higher plants, with the number of SBE isoforms being species-specific. This study isolated the SBEIII cDNA sequence (3,780 bp), designated TaSBEIII (accession no. JQ346193), from common wheat (Triticum aestivum L.) using the RACE method, revealing that the SBEIII gene exists in common wheat. The open reading frame of TaSBEIII was 2,748 bp. The predicted protein of 916 amino acids contained the specific characteristics of the SBEIII protein: four highly conserved regions and a central (α/β)(8) barrel domain. The SBE activity of the protein expressed in Escherichia coli (BL21) was also measured and verified. During the wheat grain filling period, TaSBEIII was constitutively expressed. The role of the TaSBEIII gene in starch synthesis is discussed.