| ABSTRACT:Starch-branching enzyme (BE) catalyses the formation of branch points by cleaving the a-1,4linkage in polyglucans and reattaching the chain via an a-1,6linkage. Three types of BE isoforms (BEI, BEII, and BEIII) exist in higher plants, with the number of BE isoforms being species specific. This study newly isolated the BEⅢ cDNA sequence (3780bp), designated as TaSBEIII, from common wheat (Triticum aestivum L.) using the rapid amplification of cDNA Ends (RACE) method. The open reading frame (ORF) of the TaSBEⅢ gene was2748bp, and it encoded a predicated protein of916amino acids. TaBEⅢ protein contained the specific characteristics of BEIII protein:four highly conserved regions and a central (a/β)8barrel domain.The cDNA sequences of26starch synthesis genes were identified in common wheat, and their transcript levels were measured using quantitative real-time RT-PCR to assess the function of individual genes and the regulatory mechanism in wheat endosperm. The expression patterns of26genes in wheat endosperm were classified into three groups. The genes in group1were richly expressed in the early stage of grain development and may be involved in the construction of fundamental cell machinery, synthesis of glucan primers, and initiation of starch granules. The genes in group2were highly expressed during the middle and late stages of grain development, showed similar accumulation rates to endosperm starch, and are presumed to play a crucial role in starch production. The genes in group3were scantily expressed throughout the grain development period and might be associated with transitory starch synthesis. Transcription of the negative transcription factor TaRSRl was high at the early and late stages of grain development, but low during the middle stage. The expression pattern of TaRSRl was almost opposite that of the group2starch synthesis genes, indicating that TaRSRl might negatively regulate the expression of many endosperm starch synthesis genes during grain development. |
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