Occurrence of two isoforms of granule-bound starch synthase II (GBSS II) gene in Cassava (Manihot esculenta Crantz)

摘要

Cassava (Manihot esculenta) is a major source of starch in tropical and subtropical countries. The genomic organization of the granule-bound starch synthase II (GBSS I) in cassava was examined to increase starch biosynthesis knowledge and facilitate the production of modified starches in cassava. Six genomic clones encoding fragment of granule-bound starch synthase II (GBSS II) gene were produced by PCR amplification of genomic DNA from a primer pair. Sequence analyses revealed that the clones were of two types: pOYE303-4 and pOYE303-5. The insert in pOYE303-4 (accession no. HM038440) was 1690 nucleotides long and encoded a polypeptide of 122 amino acids with molecular weight of 118.52 kDa and calculated pI of 9.67. In contrast, pOYE 303-5 (accession no. HM046981), encoded 118 amino acids with a molecular weight of 13.22 kDa and pI of 9.59. HM038440 and HM046981 had 99.4% identity at nucleotide and amino acid levels. Phylogenetic analysis showed that the two isolated gbss II sequences were not the same but belonged to the same dicot group and closely related to R. communis and V. vinifera gbss II proteins. In silico identification of introns revealed different number of introns in the two sequences: four in HM038440 and two in HM046981. The results of sequence analyses, phylogenetic study and in silico identification of intron suggested that cassava genome contains two isoform of GBSS II.