A novel Ta.AGP.S.1b transcript in Chinese common wheat (Triticum aestivum L.)

ADP-glucose pyrophosphorylase (AGPase), the key enzyme of starch synthesis in plants, is composed of two small and two large subunits, and has plastidial and cytosolic isoforms. In kernels of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), transcripts for cytosolic (Ta.AGP.S1a) and plastidial (Ta.AGP.S1b) small subunits of AGPase were encoded by the same gene (Ta.AGP.S.1) by use of the alternative first exons. In this study, a cDNA sequence (1631 bp) [NCBI: EU586278] encoding a novel Ta.AGP.S1b transcript was isolated in kernels of Chinese common wheat cultivars. Compared with another Ta.AGP.S1b transcript [NCBI: FJ643609] isolated in kernels of non-Chinese wheat cultivars, EU586278 lacked a long fragment (117 bp) at its 5'terminal, resulting in a shorten transit peptide. The lacked fragments of Ta.AGP.S1b (EU586278) were universally found in surveyed 22 Chinese common wheat cultivars. Partial genomic DNA sequence [NCBI: FJ907395] of Ta.AGP.S.1 gene, which was corresponded to 5'terminal of EU586278 transcript, was also isolated in Chinese common cultivars and sequencing indicated that FJ907395 contained the corresponding lacked fragment of EU586278 transcript, inferring the lacked fragment in EU586278 transcript was not present in the genome, but possibly occurred at transcription level. Using TargetP software, the predicated transit peptide of putative plastidial SSU encoded by EU586278 contained merely 25 amino acids, considerably shorter than those of other plant AGP. S.1bs (54-70 amino acids). Phylogenetic tree analysis indicated that the amino acid sequence of EU586278 transit peptide was not clustered together with those of other wheat Ta.AGP.S1bs [NCBI: AF536819 and FJ643609] and barley AGP.S1b [NCBI: Z48563]. These implied that EU586278 could be a novel Ta.AGP.S1b transcript. Semi-quantitative PCR analysis indicated that transcripts of EU586278 were abundantly expressed in leaf, moderately in endosperm and stem, and weakly in root.