Somatic embryogenesis and transformation of cassava for enhanced starch production
Cassava (Manihot esculenta Crantz), a member of the family Euphorbiaceae, is one of the most important food crops of sub-Saharan Africa. One of the constraints for cassava starch production is the long growing season. Cassava typically takes 9-12 months to yield a good harvest. This is longer than other major starch-producing crops such as corn and potatoes. We report here the generation of transgenic cassava with increased starch biosynthesis capacity. This was achieved by enhancing the activity of ADP-glucose pyrophosphorylase (AGPase), the rate-limiting enzyme in the starch biosynthesis, in transgenic cassava. To do this, we transformed cassava with a modified E. coli glgC gene encoding AGPase. The glgC gene was modified by site-directed mutagenesis (K296E/G336D) to remove the allosteric regulation (enhancement by fructose1,6-P and inhibition by AMP) sites and to increase the velocity of the enzyme. Root-specific expression of the glgC gene product was achieved using the tuber-specific patatin promoter of potato. We obtained antibiotic-resistant putative transformed plants which have been shown to have integrated and expressed the transgene by PCR, Southern blot, RT-PCR and enzyme activity analyses. AGPase enzyme activity in transformed plants was increased by more than 65%. Significantly, transgenic plants expressing the bacterial glgC gene had two-fold greater top (leaf and stem) and root biomass than wild-type plants grown in the greenhouse.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:cassava adp glucose pyrophosphorylase starch somatic embryogenesis transformation
Date of Publication:01/01/2003