Characterization of the GBSSI Gene Involved in Starch Waxy Mutation in Cassava (Manihot esculenta Crantz.)

Cassava is an important source of starch in tropics. Cassava starch derivatives are traded in the international markets making it a potential cash crop for small holder farmers. Diversification of starch sources was not known for cassava until in 2005 when a natural source of amylose-free starch (waxy) was by serendipity discovered at the International Center for Tropical Agriculture (CIAT). In nature other amylose-free starch sources has been discovered and exploited commercially such as in potato, wheat, maize and rice. In all these crops the responsible gene for this trait was the granule bound starch synthase – I (GBSSI). In 2007, it was also confirmed that the GBBSI gene was responsible for waxy starch in cassava.  Since, then six novel cassava germplasm sources for this mutation have been observed. The objective of this study was to fully characterize the six new sources of the waxy trait in cassava. A full-length genomic DNA sequence of GBSSI was isolated and characterized on 10 non-waxy and 20 waxy cassava genotypes, including the original source AM206-5.  Our results confirmed the recessive nature of the mutation while suggested that more than one allelic version of this gene is present in cassava indicating a potential complex expression of the trait depending the genetic background in which it expresses.