Starch Branching Enzyme I from Cassava (Manihot esculenta Crantz): Genomic Organization, Intron Identification and Phylogenetic Analysis

Cassava (Manihot esculenta) is a major source of starch in tropical and subtropical countries. The genomic organization of the starch branching enzyme I (SBE I) in cassava was examined to increase starch biosynthesis knowledge and facilitate the production of modified starch in cassava. Three genomic clones encoding a fragment of SBE I gene were produced by PCR amplification of genomic DNA from a primer pair. Sequence analyses revealed that the insert in the clones had complete homology at both nucleotide and amino acid levels. One of the clones, pOYE303-6-1 (accession no. HM046982) was 502 base pair long. HM046982 encoded a polypeptide of 35 amino acids with molecular weight of 3.90 kDa and pI of 4.8. BLAST search retrieved Manihot esculenta sbe I cDNA (accession X77012) with 100% identity. HM046982 was rich in glutamic acid (14.3%), glycine (8.5%) and alanine (8.5%). Phylogenetic analysis showed that cassava SBE I belongs to dicot first subgroup and closely related to poplar (85%), lotus (83%), sweet potato (80%) and potato (80%). In silico identification of intron revealed that HM046982 had one intron that is 259 base pair long located between nucleotide 52 and 310 and consist of 41.7% T, 26.6% A and 16.6% C and 15.4% G. Application of the results of this study to starch modification in cassava by transgenic approach and other related DNA recombinant technologies was discussed. Abreviations: cDNA complementary DNA. PCR polymerase chain reaction. SBE-starch branching enzyme. A adenine. T thymine. C cytosine. G guanine.