Isolation of Genomic Clones Encoding Granule-bound Starch Synthase (GBSS I) 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 I (GBSS I) in cassava was examined to increase our knowledge of starch biosynthesis and facilitate the production of modified starches in cassava. Three partial genomic clones were generated and the sequence analysis revealed that they were identical at both nucleotide and amino acid levels. The insert in one of the clones, pOYE303-1 (accession no. HM038439), was 731 nucleotides long and encoded a partial protein of 124 amino acid s with predicted molecular weight of 13.65 kDa and calculated 10.01 isoelectric point. HM038439 contained the first conserved domains of GBSS including the KTGG motif responsible for ADP-glucose binding site. Phylogenetic analysis revealed that cassava GBSS I belongs to dicot subgroup and is closely related to GBSS I of potato, sweet potato and buckthorn. In silico identification by nucleotide sequence alignment between genomic and cDNA sequences revealed three putative introns in GBSS I. The longest intron was 121 bp long and was located between nucleotide 595 and 716. The implications of these findings on starch biosynthesis and modification are discussed.